listener for setup new account button

Incorporate mockup fragments

See merge request briar/briar!1395

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/AuthenticatedCipher.java

@@ -1,12 +1,11 @@
-package org.briarproject.bramble.crypto;
+package org.briarproject.bramble.api.crypto;
 
-import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.security.GeneralSecurityException;
 
 @NotNullByDefault
-interface AuthenticatedCipher {
+public interface AuthenticatedCipher {
 
 	/**
 	 * Initializes this cipher for encryption or decryption with a key and an

bramble-api/src/main/java/org/briarproject/bramble/api/identity/IdentityManager.java

@@ -26,6 +26,11 @@ public interface IdentityManager {
 	 */
 	void registerIdentity(Identity i);
 
+	/**
+	 * Returns the cached local identity or loads it from the database.
+	 */
+	Identity getIdentity(Transaction txn) throws DbException;
+
 	/**
 	 * Returns the cached local identity or loads it from the database.
 	 */

bramble-api/src/main/java/org/briarproject/bramble/api/properties/TransportPropertyManager.java

@@ -74,6 +74,13 @@ public interface TransportPropertyManager {
 	TransportProperties getRemoteProperties(ContactId c, TransportId t)
 			throws DbException;
 
+	/**
+	 * Returns the remote transport properties for the given contact and
+	 * transport.
+	 */
+	TransportProperties getRemoteProperties(Transaction txn, ContactId c,
+			TransportId t) throws DbException;
+
 	/**
 	 * Merges the given properties with the existing local properties for the
 	 * given transport.

bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java

@@ -6,6 +6,7 @@ import net.i2p.crypto.eddsa.KeyPairGenerator;
 
 import org.briarproject.bramble.api.crypto.AgreementPrivateKey;
 import org.briarproject.bramble.api.crypto.AgreementPublicKey;
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.DecryptionException;
 import org.briarproject.bramble.api.crypto.KeyPair;

bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoModule.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.KeyAgreementCrypto;
 import org.briarproject.bramble.api.crypto.PasswordStrengthEstimator;

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamDecrypterFactoryImpl.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamDecrypter;
 import org.briarproject.bramble.api.crypto.StreamDecrypterFactory;

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamDecrypterImpl.java

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.crypto;
 
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamDecrypter;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamEncrypterFactoryImpl.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamEncrypter;

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamEncrypterImpl.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamEncrypter;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;

bramble-core/src/main/java/org/briarproject/bramble/crypto/XSalsa20Poly1305AuthenticatedCipher.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.spongycastle.crypto.DataLengthException;

bramble-core/src/main/java/org/briarproject/bramble/identity/IdentityManagerImpl.java

@@ -118,6 +118,11 @@ class IdentityManagerImpl implements IdentityManager, OpenDatabaseHook {
 		return cached.getLocalAuthor();
 	}
 
+	@Override
+	public Identity getIdentity(Transaction txn) throws DbException {
+		return getCachedIdentity(txn);
+	}
+
 	@Override
 	public LocalAuthor getLocalAuthor(Transaction txn) throws DbException {
 		return getCachedIdentity(txn).getLocalAuthor();

bramble-core/src/main/java/org/briarproject/bramble/properties/TransportPropertyManagerImpl.java

@@ -294,7 +294,13 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	public TransportProperties getRemoteProperties(ContactId c, TransportId t)
 			throws DbException {
 		return db.transactionWithResult(true, txn ->
-				getRemoteProperties(txn, db.getContact(txn, c), t));
+				getRemoteProperties(txn, c, t));
+	}
+
+	@Override
+	public TransportProperties getRemoteProperties(Transaction txn,
+			ContactId c, TransportId t) throws DbException {
+		return getRemoteProperties(txn, db.getContact(txn, c), t);
 	}
 
 	@Override

bramble-core/src/test/java/org/briarproject/bramble/crypto/StreamDecrypterImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.TestUtils;

bramble-core/src/test/java/org/briarproject/bramble/crypto/StreamEncrypterImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.TestUtils;

bramble-core/src/test/java/org/briarproject/bramble/crypto/TestAuthenticatedCipher.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 

bramble-core/src/test/java/org/briarproject/bramble/crypto/XSalsa20Poly1305AuthenticatedCipherTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.crypto;
 
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.util.StringUtils;

briar-android/build.gradle

@@ -101,6 +101,7 @@ dependencies {
 	implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
 	implementation 'com.google.android.material:material:1.2.1'
 	implementation 'androidx.recyclerview:recyclerview-selection:1.1.0-rc03'
+	implementation 'org.magmacollective.darkcrystal:dark-crystal-secret-sharing-wrapper:1.1.0'
 
 	implementation 'info.guardianproject.panic:panic:1.0'
 	implementation 'info.guardianproject.trustedintents:trustedintents:0.2'

briar-android/src/main/AndroidManifest.xml

@@ -134,6 +134,34 @@
 			</intent-filter>
 		</activity>
 
+		<activity
+			android:name="org.briarproject.briar.android.account.NewOrRecoverActivity"
+			android:label="@string/activity_name_new_or_recover_account"
+			android:parentActivityName="org.briarproject.briar.android.login.StartupActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.login.StartupActivity" />
+		</activity>
+
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.DistributedBackupActivity"
+			android:label="@string/activity_name_distributed_backup"
+			android:parentActivityName="org.briarproject.briar.android.settings.SettingsActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.settings.SettingsActivity" />
+		</activity>
+
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.OldDistributedBackupActivity"
+			android:label="@string/activity_name_old_distributed_backup"
+			android:parentActivityName="org.briarproject.briar.android.settings.SettingsActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.settings.SettingsActivity" />
+		</activity>
+
+
 		<activity
 			android:name="org.briarproject.briar.android.conversation.ConversationActivity"
 			android:label="@string/app_name"

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -13,6 +13,7 @@ import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
 import org.briarproject.bramble.api.crypto.PasswordStrengthEstimator;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.EventBus;
@@ -59,7 +60,9 @@ import org.briarproject.briar.api.privategroup.PrivateGroupFactory;
 import org.briarproject.briar.api.privategroup.PrivateGroupManager;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationFactory;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 import org.briarproject.briar.api.test.TestDataCreator;
+import org.briarproject.briar.socialbackup.SocialBackupManagerImpl_Factory;
 
 import java.util.concurrent.Executor;
 
@@ -184,6 +187,9 @@ public interface AndroidComponent
 
 	Thread.UncaughtExceptionHandler exceptionHandler();
 
+	SocialBackupManager socialBackupManager();
+    DatabaseComponent databaseComponent();
+
 	void inject(SignInReminderReceiver briarService);
 
 	void inject(BriarService briarService);

briar-android/src/main/java/org/briarproject/briar/android/BriarService.java

@@ -46,6 +46,7 @@ import static android.content.Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
 import static android.content.Intent.FLAG_ACTIVITY_NO_ANIMATION;
 import static android.os.Build.VERSION.SDK_INT;
+import static android.os.Process.myPid;
 import static androidx.core.app.NotificationCompat.VISIBILITY_SECRET;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
@@ -59,6 +60,7 @@ import static org.briarproject.briar.api.android.AndroidNotificationManager.ONGO
 import static org.briarproject.briar.api.android.AndroidNotificationManager.ONGOING_CHANNEL_OLD_ID;
 import static org.briarproject.briar.api.android.AndroidNotificationManager.ONGOING_NOTIFICATION_ID;
 import static org.briarproject.briar.api.android.LockManager.ACTION_LOCK;
+import static org.briarproject.briar.api.android.LockManager.EXTRA_PID;
 
 public class BriarService extends Service {
 
@@ -210,7 +212,12 @@ public class BriarService extends Service {
 	@Override
 	public int onStartCommand(Intent intent, int flags, int startId) {
 		if (ACTION_LOCK.equals(intent.getAction())) {
-			lockManager.setLocked(true);
+			int pid = intent.getIntExtra(EXTRA_PID, -1);
+			if (pid == myPid()) lockManager.setLocked(true);
+			else if (LOG.isLoggable(WARNING)) {
+				LOG.warning("Tried to lock process " + pid + " but this is " +
+						myPid());
+			}
 		}
 		return START_NOT_STICKY; // Don't restart automatically if killed
 	}

briar-android/src/main/java/org/briarproject/briar/android/account/LockManagerImpl.java

@@ -32,8 +32,10 @@ import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 
 import static android.app.AlarmManager.ELAPSED_REALTIME;
+import static android.app.PendingIntent.FLAG_UPDATE_CURRENT;
 import static android.app.PendingIntent.getService;
 import static android.content.Context.ALARM_SERVICE;
+import static android.os.Process.myPid;
 import static android.os.SystemClock.elapsedRealtime;
 import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.logging.Level.WARNING;
@@ -75,23 +77,25 @@ public class LockManagerImpl implements LockManager, Service, EventListener {
 	LockManagerImpl(Application app, SettingsManager settingsManager,
 			AndroidNotificationManager notificationManager,
 			@DatabaseExecutor Executor dbExecutor) {
-		this.appContext = app.getApplicationContext();
+		appContext = app.getApplicationContext();
 		this.settingsManager = settingsManager;
 		this.notificationManager = notificationManager;
 		this.dbExecutor = dbExecutor;
-		this.alarmManager =
+		alarmManager =
 				(AlarmManager) appContext.getSystemService(ALARM_SERVICE);
 		Intent i =
 				new Intent(ACTION_LOCK, null, appContext, BriarService.class);
-		this.lockIntent = getService(appContext, 0, i, 0);
-		this.timeoutNever = Integer.valueOf(
+		i.putExtra(EXTRA_PID, myPid());
+		// When not using FLAG_UPDATE_CURRENT, the intent might have no extras
+		lockIntent = getService(appContext, 0, i, FLAG_UPDATE_CURRENT);
+		timeoutNever = Integer.parseInt(
 				appContext.getString(R.string.pref_lock_timeout_value_never));
-		this.timeoutDefault = Integer.valueOf(
+		timeoutDefault = Integer.parseInt(
 				appContext.getString(R.string.pref_lock_timeout_value_default));
-		this.timeoutMinutes = timeoutNever;
+		timeoutMinutes = timeoutNever;
 
 		// setting this in the constructor makes #getValue() @NonNull
-		this.lockable.setValue(false);
+		lockable.setValue(false);
 	}
 
 	@Override
@@ -148,7 +152,7 @@ public class LockManagerImpl implements LockManager, Service, EventListener {
 		boolean oldValue = lockable.getValue();
 		boolean newValue = hasScreenLock(appContext) && lockableSetting;
 		if (oldValue != newValue) {
-			this.lockable.setValue(newValue);
+			lockable.setValue(newValue);
 		}
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/account/NewOrRecoverActivity.java

@@ -0,0 +1,47 @@
+package org.briarproject.briar.android.account;
+
+import android.content.Intent;
+import android.os.Bundle;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BaseActivity;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TASK;
+import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
+import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
+import static android.content.Intent.FLAG_ACTIVITY_TASK_ON_HOME;
+
+public class NewOrRecoverActivity extends BaseActivity implements
+		BaseFragment.BaseFragmentListener, SetupNewAccountChosenListener {
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void onCreate(Bundle state) {
+		super.onCreate(state);
+		// fade-in after splash screen instead of default animation
+		overridePendingTransition(R.anim.fade_in, R.anim.fade_out);
+        setContentView(R.layout.activity_fragment_container);
+		NewOrRecoverFragment fragment = NewOrRecoverFragment.newInstance();
+		showInitialFragment(fragment);
+	}
+
+	@Override
+	public void setupNewAccountChosen () {
+		finish();
+		Intent i = new Intent(this, SetupActivity.class);
+		i.addFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP |
+				FLAG_ACTIVITY_CLEAR_TASK | FLAG_ACTIVITY_TASK_ON_HOME);
+		startActivity(i);
+	}
+
+	@Override
+	public void runOnDbThread(Runnable runnable) {
+
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/account/NewOrRecoverFragment.java

@@ -0,0 +1,63 @@
+package org.briarproject.briar.android.account;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+public class NewOrRecoverFragment extends BaseFragment {
+
+	public static final String TAG = NewOrRecoverFragment.class.getName();
+
+	protected SetupNewAccountChosenListener listener;
+
+	public static NewOrRecoverFragment newInstance() {
+		Bundle bundle = new Bundle();
+		NewOrRecoverFragment fragment = new NewOrRecoverFragment();
+		fragment.setArguments(bundle);
+		return fragment;
+	}
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.setup_title);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable
+			ViewGroup container, @Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_new_or_recover,
+				container, false);
+		Button button = view.findViewById(R.id.buttonSetupNewAccount);
+		button.setOnClickListener(e -> {
+			listener.setupNewAccountChosen();
+		});
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (SetupNewAccountChosenListener) context;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/account/SetupNewAccountChosenListener.java

@@ -0,0 +1,8 @@
+package org.briarproject.briar.android.account;
+
+import androidx.annotation.UiThread;
+
+public interface SetupNewAccountChosenListener {
+	@UiThread
+	void setupNewAccountChosen();
+}

briar-android/src/main/java/org/briarproject/briar/android/account/UnlockActivity.java

@@ -77,7 +77,7 @@ public class UnlockActivity extends BaseActivity {
 
 	@Override
 	protected void onActivityResult(int requestCode, int resultCode,
-			Intent data) {
+			@Nullable Intent data) {
 		super.onActivityResult(requestCode, resultCode, data);
 		if (requestCode == REQUEST_KEYGUARD_UNLOCK) {
 			if (resultCode == RESULT_OK) unlock();

briar-android/src/main/java/org/briarproject/briar/android/activity/ActivityComponent.java

@@ -2,10 +2,13 @@ package org.briarproject.briar.android.activity;
 
 import android.app.Activity;
 
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.briar.android.AndroidComponent;
 import org.briarproject.briar.android.StartupFailureActivity;
 import org.briarproject.briar.android.account.AuthorNameFragment;
 import org.briarproject.briar.android.account.DozeFragment;
+import org.briarproject.briar.android.account.NewOrRecoverActivity;
+import org.briarproject.briar.android.account.NewOrRecoverFragment;
 import org.briarproject.briar.android.account.SetPasswordFragment;
 import org.briarproject.briar.android.account.SetupActivity;
 import org.briarproject.briar.android.account.UnlockActivity;
@@ -77,20 +80,31 @@ import org.briarproject.briar.android.sharing.ShareBlogFragment;
 import org.briarproject.briar.android.sharing.ShareForumActivity;
 import org.briarproject.briar.android.sharing.ShareForumFragment;
 import org.briarproject.briar.android.sharing.SharingModule;
+//import org.briarproject.briar.android.socialbackup.CustodianDisplayFragment;
+import org.briarproject.briar.android.socialbackup.CustodianSelectorFragment;
+import org.briarproject.briar.android.socialbackup.DistributedBackupActivity;
+import org.briarproject.briar.android.socialbackup.ExistingBackupFragment;
+import org.briarproject.briar.android.socialbackup.OldDistributedBackupActivity;
+import org.briarproject.briar.android.socialbackup.ShardsSentFragment;
+import org.briarproject.briar.android.socialbackup.ThresholdSelectorFragment;
+import org.briarproject.briar.android.socialbackup.creation.CreateBackupController;
+import org.briarproject.briar.android.socialbackup.creation.CreateBackupModule;
 import org.briarproject.briar.android.splash.SplashScreenActivity;
 import org.briarproject.briar.android.test.TestDataActivity;
+import org.h2.util.New;
 
 import dagger.Component;
 
 @ActivityScope
-@Component(modules = {
+@Component(modules ={
 		ActivityModule.class,
 		BlogModule.class,
 		CreateGroupModule.class,
 		GroupInvitationModule.class,
 		GroupMemberModule.class,
 		GroupRevealModule.class,
-		SharingModule.SharingLegacyModule.class
+		SharingModule.SharingLegacyModule.class,
+		CreateBackupModule.class
 }, dependencies = AndroidComponent.class)
 public interface ActivityComponent {
 
@@ -182,6 +196,8 @@ public interface ActivityComponent {
 
 	void inject(CrashReportActivity crashReportActivity);
 
+	void inject(NewOrRecoverActivity newOrRecoverActivity);
+
 	// Fragments
 
 	void inject(AuthorNameFragment fragment);
@@ -238,4 +254,21 @@ public interface ActivityComponent {
 
 	void inject(ConfirmAvatarDialogFragment fragment);
 
+	void inject(ThresholdSelectorFragment thresholdSelectorFragment);
+
+	void inject(DistributedBackupActivity distributedBackupActivity);
+//    void inject(CreateBackupController createBackupController);
+//	void inject(CustodianDisplayFragment custodianDisplayFragment);
+
+	void inject(DatabaseComponent databaseComponent);
+
+	void inject(CustodianSelectorFragment custodianSelectorFragment);
+
+	void inject(ShardsSentFragment shardsSentFragment);
+
+	void inject(ExistingBackupFragment existingBackupFragment);
+
+	void inject(NewOrRecoverFragment newOrRecoverFragment);
+
+	void inject(OldDistributedBackupActivity oldDistributedBackupActivity);
 }

briar-android/src/main/java/org/briarproject/briar/android/contactselection/BaseContactSelectorFragment.java

@@ -56,8 +56,11 @@ public abstract class BaseContactSelectorFragment<I extends SelectableContactIte
 
 		Bundle args = requireArguments();
 		byte[] b = args.getByteArray(GROUP_ID);
-		if (b == null) throw new IllegalStateException("No GroupId");
-		groupId = new GroupId(b);
+//		if (b == null) throw new IllegalStateException("No GroupId");
+		// TODO find what the groupId should be when selecting custodians
+		if (b != null) {
+			groupId = new GroupId(b);
+		}
 	}
 
 	@Override

briar-android/src/main/java/org/briarproject/briar/android/contactselection/ContactSelectorFragment.java

@@ -18,7 +18,7 @@ public abstract class ContactSelectorFragment extends
 
 	public static final String TAG = ContactSelectorFragment.class.getName();
 
-	private Menu menu;
+	protected Menu menu;
 
 	@Override
 	protected ContactSelectorAdapter getAdapter(Context context,

briar-android/src/main/java/org/briarproject/briar/android/login/StartupActivity.java

@@ -7,6 +7,7 @@ import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.BriarService;
+import org.briarproject.briar.android.account.NewOrRecoverActivity;
 import org.briarproject.briar.android.account.SetupActivity;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BaseActivity;
@@ -107,7 +108,7 @@ public class StartupActivity extends BaseActivity implements
 	private void onAccountDeleted() {
 		setResult(RESULT_CANCELED);
 		finish();
-		Intent i = new Intent(this, SetupActivity.class);
+		Intent i = new Intent(this, NewOrRecoverActivity.class);
 		i.addFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP |
 				FLAG_ACTIVITY_CLEAR_TASK | FLAG_ACTIVITY_TASK_ON_HOME);
 		startActivity(i);

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/CustodianSelectorFragment.java

@@ -0,0 +1,93 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.view.MenuItem;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.socialbackup.creation.CreateBackupController;
+import org.briarproject.briar.android.contactselection.BaseContactSelectorAdapter;
+import org.briarproject.briar.android.contactselection.ContactSelectorController;
+import org.briarproject.briar.android.contactselection.ContactSelectorFragment;
+import org.briarproject.briar.android.contactselection.SelectableContactItem;
+import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;
+
+import java.util.Collection;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+
+import static java.util.Objects.requireNonNull;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class CustodianSelectorFragment extends ContactSelectorFragment {
+
+	public static final String TAG = CustodianSelectorFragment.class.getName();
+
+	@Inject
+	CreateBackupController controller;
+
+	public static CustodianSelectorFragment newInstance() {
+		Bundle args = new Bundle();
+
+		CustodianSelectorFragment fragment = new CustodianSelectorFragment();
+		fragment.setArguments(args);
+
+		return fragment;
+	}
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+
+		requireActivity().setTitle(R.string.title_select_custodians);
+	}
+
+	@Override
+	protected ContactSelectorController<SelectableContactItem> getController() {
+		return controller;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	protected void onSelectionChanged() {
+		super.onSelectionChanged();
+		if (menu == null) return;
+		MenuItem item = menu.findItem(R.id.action_contacts_selected);
+		if (item == null) return;
+
+		BaseContactSelectorAdapter a = adapter;
+		selectedContacts = a.getSelectedContactIds();
+
+		int n = selectedContacts.size();
+		int min = 2;
+		boolean enough = n >= min;
+
+		item.setVisible(enough);
+		if (n == 0) {
+			Toast.makeText(getContext(), String.format(getString(R.string.select_at_least_n_contacts), min),
+					Toast.LENGTH_SHORT).show();
+		} else if (n < min) {
+			Toast.makeText(getContext(), String.format(getString(R.string.select_at_least_n_more_contacts), min - n),
+					Toast.LENGTH_SHORT).show();
+		}
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/DarkCrystalImpl.java

@@ -0,0 +1,46 @@
+package org.briarproject.briar.android.socialbackup;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.briar.api.socialbackup.Shard;
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+import org.magmacollective.darkcrystal.secretsharingwrapper.SecretSharingWrapper;
+
+import java.security.GeneralSecurityException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.SECRET_ID_BYTES;
+
+public class DarkCrystalImpl implements DarkCrystal {
+
+	@Override
+	public List<Shard> createShards(SecretKey secret, int numShards,
+			int threshold) {
+		Random random = new Random();
+		byte[] secretId = new byte[SECRET_ID_BYTES];
+		random.nextBytes(secretId);
+		List<byte[]> shardsBytes = SecretSharingWrapper.share(secret.getBytes(), numShards, threshold);
+		List<Shard> shards = new ArrayList<>(numShards);
+		for (byte[] shardBytes : shardsBytes) {
+			shards.add(new Shard(secretId, shardBytes));
+		}
+		return shards;
+	}
+
+	@Override
+	public SecretKey combineShards(List<Shard> shards) throws
+			GeneralSecurityException {
+		// Check each shard has the same secret Id
+		byte[] secretId = shards.get(0).getSecretId();
+		for (Shard shard : shards) {
+			if (!Arrays.equals(shard.getSecretId(), secretId)) throw new GeneralSecurityException();
+		}
+        List<byte[]> shardsBytes = new ArrayList<>(shards.size());
+		for (Shard shard : shards) {
+			shardsBytes.add(shard.getShard());
+		}
+		byte[] secretBytes = SecretSharingWrapper.combine(shardsBytes);
+		return new SecretKey(secretBytes);
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/DistributedBackupActivity.java

@@ -0,0 +1,85 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.contactselection.ContactSelectorListener;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+
+import java.util.Collection;
+import java.util.List;
+
+import javax.inject.Inject;
+
+public class DistributedBackupActivity extends BriarActivity implements
+		BaseFragment.BaseFragmentListener, ContactSelectorListener,
+		ThresholdDefinedListener, ShardsSentDismissedListener {
+
+	private Collection<ContactId> custodians;
+
+	@Inject
+    public SocialBackupManager socialBackupManager;
+
+	@Inject
+    public DatabaseComponent db;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_distributed_backup);
+        // TODO here we should check if we already have a backup
+
+		try {
+			db.transaction(false, txn -> {
+				BackupMetadata backupMetadata = socialBackupManager.getBackupMetadata(txn);
+				 if (backupMetadata == null) {
+				CustodianSelectorFragment fragment =
+						CustodianSelectorFragment.newInstance();
+					 showInitialFragment(fragment);
+				 } else {
+					 ExistingBackupFragment fragment = ExistingBackupFragment.newInstance(backupMetadata);
+					 showInitialFragment(fragment);
+				 }
+			});
+		} catch (DbException e) {
+			e.printStackTrace();
+		}
+	}
+
+	@Override
+	public void contactsSelected(Collection<ContactId> contacts) {
+		Toast.makeText(this,
+				String.format("selected %d contacts", contacts.size()),
+				Toast.LENGTH_SHORT).show();
+		custodians = contacts;
+		ThresholdSelectorFragment fragment = ThresholdSelectorFragment.newInstance(contacts.size());
+		showNextFragment(fragment);
+	}
+
+	@Override
+	public void thresholdDefined(int threshold) throws DbException {
+		db.transaction(false, txn -> {
+			socialBackupManager.createBackup(txn, (List<ContactId>) custodians, threshold);
+			ShardsSentFragment fragment = new ShardsSentFragment();
+			showNextFragment(fragment);
+		});
+	}
+
+	@Override
+	public void shardsSentDismissed() {
+		finish();
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ExistingBackupFragment.java

@@ -0,0 +1,85 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.TextView;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+public class ExistingBackupFragment extends BaseFragment {
+
+	private static final String THRESHOLD = "threshold";
+	private static final String CUSTODIANS = "custodians";
+	public static final String TAG = ExistingBackupFragment.class.getName();
+
+	public static ExistingBackupFragment newInstance(
+			BackupMetadata backupMetadata) {
+		Bundle bundle = new Bundle();
+		List<Author> custodians = backupMetadata.getCustodians();
+		ArrayList custodianNames = new ArrayList();
+	    for (Author custodian : custodians) {
+	    	custodianNames.add(custodian.getName());
+	    }
+	    bundle.putStringArrayList(CUSTODIANS, custodianNames);
+		bundle.putInt(THRESHOLD, backupMetadata.getThreshold());
+		ExistingBackupFragment fragment = new ExistingBackupFragment();
+		fragment.setArguments(bundle);
+		return fragment;
+	}
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_distributed_backup);
+
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable
+			ViewGroup container, @Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_existing_backup,
+				container, false);
+		Bundle args = requireArguments();
+        ArrayList<String> custodianNames = args.getStringArrayList(CUSTODIANS);
+        String custodianNamesString = "";
+        for (String custodianName : custodianNames) {
+          	custodianNamesString += custodianName + ", ";
+        }
+        TextView textViewThreshold = view.findViewById(R.id.textViewThreshold);
+        textViewThreshold.setText(String.format("%d of %d contacts needed to restore account", args.getInt(THRESHOLD), custodianNames.size()));
+        TextView textViewCustodians = view.findViewById(R.id.textViewCustodians);
+        textViewCustodians.setText(custodianNamesString);
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+//		listener = (ShardsSentDismissedListener) context;
+	}
+
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/OldDistributedBackupActivity.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.contactselection.ContactSelectorListener;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import java.util.Collection;
+
+public class OldDistributedBackupActivity extends BriarActivity
+		implements BaseFragment.BaseFragmentListener, ContactSelectorListener {
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_distributed_backup);
+
+//		CustodianDisplayFragment fragment =
+//				CustodianDisplayFragment.newInstance();
+//
+//		showInitialFragment(fragment);
+	}
+
+	@Override
+	public void contactsSelected(Collection<ContactId> contacts) {
+		// do nothing
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ShardsSentDismissedListener.java

@@ -0,0 +1,10 @@
+package org.briarproject.briar.android.socialbackup;
+
+import androidx.annotation.UiThread;
+
+public interface ShardsSentDismissedListener {
+
+	@UiThread
+	void shardsSentDismissed();
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ShardsSentFragment.java

@@ -0,0 +1,60 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+public class ShardsSentFragment extends BaseFragment {
+
+    public static final String TAG = ShardsSentFragment.class.getName();
+
+    protected ShardsSentDismissedListener listener;
+
+    @Override
+    public void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        requireActivity().setTitle(R.string.title_distributed_backup);
+    }
+
+    @Nullable
+    @Override
+    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
+        View view = inflater.inflate(R.layout.fragment_shards_sent,
+                container, false);
+
+        Button button = view.findViewById(R.id.button);
+        button.setOnClickListener(e -> {
+            listener.shardsSentDismissed();
+        });
+
+        return view;
+    }
+
+    @Override
+    public void onAttach(Context context) {
+        super.onAttach(context);
+        listener = (ShardsSentDismissedListener) context;
+    }
+
+
+    @Override
+    public String getUniqueTag() {
+        return TAG;
+    }
+
+    @Override
+    public void injectFragment(ActivityComponent component) {
+        component.inject(this);
+    }
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ThresholdDefinedListener.java

@@ -0,0 +1,12 @@
+package org.briarproject.briar.android.socialbackup;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import androidx.annotation.UiThread;
+
+public interface ThresholdDefinedListener {
+
+	@UiThread
+	void thresholdDefined(int threshold) throws DbException;
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ThresholdSelectorFragment.java

@@ -0,0 +1,169 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.Menu;
+import android.view.MenuInflater;
+import android.view.MenuItem;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.ImageView;
+import android.widget.SeekBar;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.contactselection.ContactSelectorListener;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.magmacollective.darkcrystal.secretsharingwrapper.SecretSharingWrapper;
+
+import static java.util.Objects.requireNonNull;
+
+public class ThresholdSelectorFragment extends BaseFragment {
+
+    public static final String TAG = ThresholdSelectorFragment.class.getName();
+    private static final String NUMBER_CUSTODIANS = "numberCustodians";
+
+    protected ThresholdDefinedListener listener;
+
+    // TODO this should be the actual number of custodians
+    private int numberOfCustodians;
+    private int threshold;
+    private int recommendedThreshold;
+    private SeekBar seekBar;
+    private TextView thresholdRepresentation;
+    private TextView message;
+    private TextView mOfn;
+
+    public static ThresholdSelectorFragment newInstance(int numberCustodians) {
+        Bundle bundle = new Bundle();
+        bundle.putInt(NUMBER_CUSTODIANS, numberCustodians);
+        ThresholdSelectorFragment fragment = new ThresholdSelectorFragment();
+        fragment.setArguments(bundle);
+        return fragment;
+    }
+
+    @Override
+    public void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        requireActivity().setTitle(R.string.title_define_threshold);
+    }
+
+    @Nullable
+    @Override
+    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
+        View view = inflater.inflate(R.layout.fragment_select_threshold,
+                container, false);
+	    Bundle args = requireArguments();
+	    numberOfCustodians = args.getInt(NUMBER_CUSTODIANS);
+
+        seekBar = view.findViewById(R.id.seekBar);
+        thresholdRepresentation = view.findViewById(R.id.textViewThresholdRepresentation);
+        message = view.findViewById(R.id.textViewMessage);
+        mOfn = view.findViewById(R.id.textViewmOfn);
+        int max = numberOfCustodians - 3;
+        seekBar.setMax(max);
+        seekBar.setOnSeekBarChangeListener(new SeekBarListener());
+        recommendedThreshold = SecretSharingWrapper.defaultThreshold(numberOfCustodians);
+        threshold = recommendedThreshold;
+        seekBar.setProgress(threshold - 2);
+
+        thresholdRepresentation.setText(buildThresholdRepresentationString());
+        setmOfnText();
+        return view;
+//        return super.onCreateView(inflater, container, savedInstanceState);
+    }
+
+    private void setmOfnText() {
+        mOfn.setText(String.format("%d of %d contacts needed to recover your account", threshold, numberOfCustodians));
+    }
+
+    @Override
+    public void onAttach(Context context) {
+        super.onAttach(context);
+        listener = (ThresholdDefinedListener) context;
+    }
+
+
+    @Override
+    public String getUniqueTag() {
+        return TAG;
+    }
+
+    @Override
+    public void injectFragment(ActivityComponent component) {
+        component.inject(this);
+    }
+
+    @Override
+    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+        inflater.inflate(R.menu.define_threshold_actions, menu);
+        super.onCreateOptionsMenu(menu, inflater);
+    }
+
+    @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        switch (item.getItemId()) {
+            case R.id.action_threshold_defined:
+                try {
+                    listener.thresholdDefined(threshold);
+                } catch (DbException e) {
+                    e.printStackTrace();
+                }
+                return true;
+            default:
+                return super.onOptionsItemSelected(item);
+        }
+    }
+
+    private String buildThresholdRepresentationString () {
+        String thresholdRepresentationText = "";
+        for (int i = 0; i < threshold; i++) {
+            thresholdRepresentationText += getString(R.string.filled_bullet);
+        }
+        for (int i = 0; i < (numberOfCustodians - threshold); i++) {
+            thresholdRepresentationText += getString(R.string.linear_bullet);
+        }
+        return thresholdRepresentationText;
+    }
+
+    private class SeekBarListener implements SeekBar.OnSeekBarChangeListener {
+
+        @Override
+        public void onProgressChanged(SeekBar seekBar, int progress,
+                boolean fromUser) {
+	        threshold = progress + 2;
+
+            thresholdRepresentation.setText(
+                    buildThresholdRepresentationString()
+            );
+            setmOfnText();
+
+            int sanityLevel = SecretSharingWrapper.thresholdSanity(threshold, numberOfCustodians);
+            int text = R.string.threshold_secure;
+            if (threshold == recommendedThreshold) text = R.string.threshold_recommended;
+            if (sanityLevel < -1) text = R.string.threshold_low_insecure;
+            if (sanityLevel > 0) text = R.string.threshold_high_insecure;
+            message.setText(text);
+            // TODO change colour of thresholdRepresentation to green/red based on sanityLevel
+        }
+
+        @Override
+        public void onStartTrackingTouch(SeekBar seekBar) {
+            // do nothing
+        }
+
+        @Override
+        public void onStopTrackingTouch(SeekBar seekBar) {
+            // do nothing
+        }
+
+    }
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/creation/CreateBackupController.java

@@ -0,0 +1,26 @@
+package org.briarproject.briar.android.socialbackup.creation;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.android.contactselection.ContactSelectorController;
+import org.briarproject.briar.android.contactselection.SelectableContactItem;
+import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;
+
+import java.util.Collection;
+
+import androidx.annotation.Nullable;
+
+@NotNullByDefault
+public interface CreateBackupController
+		extends ContactSelectorController<SelectableContactItem> {
+
+	void createGroup(String name,
+			ResultExceptionHandler<GroupId, DbException> result);
+
+	void sendInvitation(GroupId g, Collection<ContactId> contacts,
+			@Nullable String text,
+			ResultExceptionHandler<Void, DbException> result);
+
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/creation/CreateBackupControllerImpl.java

@@ -0,0 +1,206 @@
+package org.briarproject.briar.android.socialbackup.creation;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.NoSuchContactException;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.briar.android.contactselection.ContactSelectorControllerImpl;
+import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;
+import org.briarproject.briar.api.identity.AuthorManager;
+import org.briarproject.briar.api.privategroup.GroupMessage;
+import org.briarproject.briar.api.privategroup.GroupMessageFactory;
+import org.briarproject.briar.api.privategroup.PrivateGroup;
+import org.briarproject.briar.api.privategroup.PrivateGroupFactory;
+import org.briarproject.briar.api.privategroup.PrivateGroupManager;
+import org.briarproject.briar.api.privategroup.invitation.GroupInvitationFactory;
+import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@Immutable
+@NotNullByDefault
+/**
+ * Derived from {@link org.briarproject.briar.android.privategroup.invitation.GroupInvitationControllerImpl}
+ */
+class CreateBackupControllerImpl extends ContactSelectorControllerImpl
+		implements CreateBackupController {
+
+	private static final Logger LOG =
+			Logger.getLogger(
+					CreateBackupControllerImpl.class.getName());
+
+	private final Executor cryptoExecutor;
+	private final ContactManager contactManager;
+	private final IdentityManager identityManager;
+	private final PrivateGroupFactory groupFactory;
+	private final GroupMessageFactory groupMessageFactory;
+	private final PrivateGroupManager groupManager;
+	private final GroupInvitationFactory groupInvitationFactory;
+	private final GroupInvitationManager groupInvitationManager;
+	private final Clock clock;
+
+	@Inject
+	CreateBackupControllerImpl(@DatabaseExecutor Executor dbExecutor,
+			@CryptoExecutor Executor cryptoExecutor,
+			LifecycleManager lifecycleManager, ContactManager contactManager,
+			IdentityManager identityManager, PrivateGroupFactory groupFactory,
+			GroupMessageFactory groupMessageFactory,
+			PrivateGroupManager groupManager,
+			GroupInvitationFactory groupInvitationFactory,
+			GroupInvitationManager groupInvitationManager, Clock clock, AuthorManager authorManager) {
+		super(dbExecutor, lifecycleManager, contactManager, authorManager);
+		this.cryptoExecutor = cryptoExecutor;
+		this.contactManager = contactManager;
+		this.identityManager = identityManager;
+		this.groupFactory = groupFactory;
+		this.groupMessageFactory = groupMessageFactory;
+		this.groupManager = groupManager;
+		this.groupInvitationFactory = groupInvitationFactory;
+		this.groupInvitationManager = groupInvitationManager;
+		this.clock = clock;
+	}
+
+	@Override
+	public void createGroup(String name,
+			ResultExceptionHandler<GroupId, DbException> handler) {
+		runOnDbThread(() -> {
+			try {
+				LocalAuthor author = identityManager.getLocalAuthor();
+				createGroupAndMessages(author, name, handler);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				handler.onException(e);
+			}
+		});
+	}
+
+	private void createGroupAndMessages(LocalAuthor author, String name,
+			ResultExceptionHandler<GroupId, DbException> handler) {
+		cryptoExecutor.execute(() -> {
+			LOG.info("Creating group...");
+			PrivateGroup group =
+					groupFactory.createPrivateGroup(name, author);
+			LOG.info("Creating new join announcement...");
+			GroupMessage joinMsg =
+					groupMessageFactory.createJoinMessage(group.getId(),
+							clock.currentTimeMillis(), author);
+			storeGroup(group, joinMsg, handler);
+		});
+	}
+
+	private void storeGroup(PrivateGroup group, GroupMessage joinMsg,
+			ResultExceptionHandler<GroupId, DbException> handler) {
+		runOnDbThread(() -> {
+			LOG.info("Adding group to database...");
+			try {
+				groupManager.addPrivateGroup(group, joinMsg, true);
+				handler.onResult(group.getId());
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				handler.onException(e);
+			}
+		});
+	}
+
+	@Override
+	protected boolean isDisabled(GroupId g, Contact c) {
+		return false;
+	}
+
+	@Override
+	public void sendInvitation(GroupId g, Collection<ContactId> contactIds,
+			@Nullable String text,
+			ResultExceptionHandler<Void, DbException> handler) {
+		runOnDbThread(() -> {
+			try {
+				LocalAuthor localAuthor = identityManager.getLocalAuthor();
+				List<Contact> contacts = new ArrayList<>();
+				for (ContactId c : contactIds) {
+					try {
+						contacts.add(contactManager.getContact(c));
+					} catch (NoSuchContactException e) {
+						// Continue
+					}
+				}
+				signInvitations(g, localAuthor, contacts, text, handler);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				handler.onException(e);
+			}
+		});
+	}
+
+	private void signInvitations(GroupId g, LocalAuthor localAuthor,
+			Collection<Contact> contacts, @Nullable String text,
+			ResultExceptionHandler<Void, DbException> handler) {
+		cryptoExecutor.execute(() -> {
+			long timestamp = clock.currentTimeMillis();
+			List<InvitationContext> contexts = new ArrayList<>();
+			for (Contact c : contacts) {
+				byte[] signature = groupInvitationFactory.signInvitation(c, g,
+						timestamp, localAuthor.getPrivateKey());
+				contexts.add(new InvitationContext(c.getId(), timestamp,
+						signature));
+			}
+			sendInvitations(g, contexts, text, handler);
+		});
+	}
+
+	private void sendInvitations(GroupId g,
+			Collection<InvitationContext> contexts, @Nullable String text,
+			ResultExceptionHandler<Void, DbException> handler) {
+		runOnDbThread(() -> {
+			try {
+				for (InvitationContext context : contexts) {
+					try {
+						groupInvitationManager.sendInvitation(g,
+								context.contactId, text, context.timestamp,
+								context.signature);
+					} catch (NoSuchContactException e) {
+						// Continue
+					}
+				}
+				//noinspection ConstantConditions
+				handler.onResult(null);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				handler.onException(e);
+			}
+		});
+	}
+
+	private static class InvitationContext {
+
+		private final ContactId contactId;
+		private final long timestamp;
+		private final byte[] signature;
+
+		private InvitationContext(ContactId contactId, long timestamp,
+				byte[] signature) {
+			this.contactId = contactId;
+			this.timestamp = timestamp;
+			this.signature = signature;
+		}
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/creation/CreateBackupModule.java

@@ -0,0 +1,18 @@
+package org.briarproject.briar.android.socialbackup.creation;
+
+import org.briarproject.briar.android.activity.ActivityScope;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class CreateBackupModule {
+
+	@ActivityScope
+	@Provides
+	CreateBackupController provideCreateGroupController(
+			CreateBackupControllerImpl createBackupController) {
+		return createBackupController;
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/api/android/LockManager.java

@@ -8,6 +8,7 @@ import androidx.lifecycle.LiveData;
 public interface LockManager {
 
 	String ACTION_LOCK = "lock";
+	String EXTRA_PID = "PID";
 
 	/**
 	 * Stops the inactivity timer when the user interacts with the app.

briar-android/src/main/res/drawable/ic_baseline_done_outline_24.xml

@@ -0,0 +1,5 @@
+<vector android:height="24dp" android:tint="#29C400"
+    android:viewportHeight="24" android:viewportWidth="24"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
+    <path android:fillColor="@android:color/white" android:pathData="M19.77,5.03l1.4,1.4L8.43,19.17l-5.6,-5.6 1.4,-1.4 4.2,4.2L19.77,5.03m0,-2.83L8.43,13.54l-4.2,-4.2L0,13.57 8.43,22 24,6.43 19.77,2.2z"/>
+</vector>

briar-android/src/main/res/layout/activity_distributed_backup.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/fragmentContainer"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/activity_preview_recovery_custodian1.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_help_recover"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_custodian_explainer" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_recovery_custodian2.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_help_recover"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_custodian_error_explainer" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_recovery_owner1.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_recovery_mode"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_owner_explainer" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_recovery_owner2.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_recovery_mode"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_owner_error_explainer" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_recovery_owner3.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_recovery_mode"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_owner_main" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_recovery_owner4.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/title_recovery_mode"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_recovery_owner_recovering" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_preview_welcome.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/setup_title"
+		app:titleTextColor="@android:color/white" />
+
+	<include layout="@layout/fragment_start" />
+
+</LinearLayout>

briar-android/src/main/res/layout/activity_welcome.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:fitsSystemWindows="true"
+	android:orientation="vertical">
+
+	<androidx.appcompat.widget.Toolbar
+		android:id="@+id/toolbar"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="?attr/colorPrimary"
+		android:minHeight="?attr/actionBarSize"
+		app:title="@string/setup_title"
+		app:titleTextColor="@android:color/white" />
+
+</LinearLayout>

briar-android/src/main/res/layout/fragment_account_recovered.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/linearLayout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingLeft="@dimen/margin_large"
+    android:paddingTop="@dimen/margin_medium"
+    android:paddingRight="@dimen/margin_large"
+    android:paddingBottom="@dimen/margin_medium">
+
+    <Button
+        android:id="@+id/button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="32dp"
+        android:text="@string/backup_done_dismiss"
+        android:textSize="24sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/textView2" />
+
+    <TextView
+        android:id="@+id/textView2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="16dp"
+        android:gravity="center"
+        android:text="@string/recovery_account_recovered"
+        android:textSize="30sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/imageView2" />
+
+    <ImageView
+        android:id="@+id/imageView2"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_marginStart="32dp"
+        android:layout_marginLeft="32dp"
+        android:layout_marginTop="8dp"
+        android:layout_marginEnd="32dp"
+        android:layout_marginRight="32dp"
+        app:layout_constraintDimensionRatio="1:1"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:srcCompat="@drawable/ic_baseline_done_outline_24" />
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_existing_backup.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	android:layout_width="match_parent"
+
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_large"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	android:layout_height="match_parent">
+
+	<TextView
+		android:id="@+id/textViewThreshold"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:gravity="center"
+		android:text="placeholder threshold"
+		android:textSize="16sp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent" />
+
+	<TextView
+		android:id="@+id/textViewCustodians"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:gravity="center"
+		android:text="@string/backup_done_info"
+		android:textSize="16sp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textViewThreshold" />
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_mockups.xml

@@ -0,0 +1,130 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent">
+
+	<LinearLayout
+		android:id="@+id/linearLayout"
+		android:layout_width="match_parent"
+		android:layout_height="match_parent"
+		android:orientation="vertical"
+		android:paddingLeft="@dimen/margin_large"
+		android:paddingTop="@dimen/margin_medium"
+		android:paddingRight="@dimen/margin_large"
+		android:paddingBottom="@dimen/margin_medium">
+
+		<TextView
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:text="Backup creation" />
+
+		<Button
+			android:id="@+id/buttonSelectThreshold"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Select Threshold" />
+
+		<Button
+			android:id="@+id/buttonShardsSent"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Shards sent" />
+
+		<TextView
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:text="Setup" />
+
+		<Button
+			android:id="@+id/buttonWelcome"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Welcome" />
+
+		<TextView
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:text="Recovery from secrect owner's point of view" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryExplainer"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Explainer" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryReceivedShard"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Shard received" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryMain1"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Main (0 shards)" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryMain2"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Main (1 shard)" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryMain3"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Recovering account…" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryAccountRecovered"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Account recovered" />
+
+		<Button
+			android:id="@+id/buttonOwnerRecoveryErrorExplainer"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Error" />
+
+		<TextView
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:text="Recovery from custodian's point of view" />
+
+		<Button
+			android:id="@+id/buttonCustodianRecoveryExplainer"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Explainer" />
+
+		<Button
+			android:id="@+id/buttonCustodianRecoveryErrorExplainer"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Error" />
+
+		<Button
+			android:id="@+id/buttonCustodianRecoveryDone"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:drawableLeft="@drawable/ic_security"
+			android:text="Done" />
+
+	</LinearLayout>
+</ScrollView>

briar-android/src/main/res/layout/fragment_new_or_recover.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:showIn="@layout/activity_preview_welcome">
+
+	<Button
+		android:id="@+id/buttonSetupNewAccount"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:drawableLeft="@drawable/ic_contacts"
+		android:text="@string/setup_new_account"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent" />
+
+	<Button
+		android:id="@+id/buttonRestoreAccount"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:drawableLeft="@drawable/ic_repeat"
+		android:text="@string/setup_restore_account"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/buttonSetupNewAccount" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_custodian_done.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium">
+
+	<TextView
+		android:id="@+id/textView2"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="16dp"
+		android:gravity="center"
+		android:text="@string/custodian_shard_sent"
+		android:textSize="30sp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/imageView2" />
+
+	<ImageView
+		android:id="@+id/imageView2"
+		android:layout_width="match_parent"
+		android:layout_height="0dp"
+		android:layout_marginStart="32dp"
+		android:layout_marginLeft="32dp"
+		android:layout_marginTop="8dp"
+		android:layout_marginEnd="32dp"
+		android:layout_marginRight="32dp"
+		app:layout_constraintDimensionRatio="1:1"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent"
+		app:srcCompat="@drawable/ic_baseline_done_outline_24" />
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_custodian_error_explainer.xml

@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_custodian2">
+
+	<TextView
+		android:id="@+id/textView1"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/custodian_recovery_failed_to_send"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<ImageView
+		android:id="@+id/imageView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView1"
+		app:srcCompat="@drawable/qr_code_error" />
+
+	<TextView
+		android:id="@+id/textView2"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_helpful_suggestions"
+		android:textSize="24sp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/imageView" />
+
+	<Button
+		android:id="@+id/button"
+		android:layout_marginTop="24dp"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:text="@string/recovery_retry"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView2" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_custodian_explainer.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_custodian1">
+
+	<TextView
+		android:id="@+id/textView"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/custodian_recovery_explainer"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<ImageView
+		android:id="@+id/imageView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView"
+		app:srcCompat="@drawable/qr_code_intro" />
+
+	<Button
+		android:id="@+id/button"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:text="@string/custodian_scan_code"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/imageView" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_owner_error_explainer.xml

@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_owner2">
+
+	<TextView
+		android:id="@+id/textView1"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_failed_to_receive"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent" />
+
+	<ImageView
+		android:id="@+id/imageView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView1"
+		app:srcCompat="@drawable/qr_code_error" />
+
+	<TextView
+		android:id="@+id/textView2"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_helpful_suggestions"
+		android:textSize="24sp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/imageView" />
+
+	<Button
+		android:id="@+id/button"
+		android:layout_marginTop="24dp"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:text="@string/recovery_retry"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView2" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_owner_explainer.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_owner1">
+
+	<TextView
+		android:id="@+id/textView"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_explainer"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<ImageView
+		android:id="@+id/imageView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textView"
+		app:srcCompat="@drawable/qr_code_intro" />
+
+	<Button
+		android:id="@+id/button"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:text="@string/recovery_begin"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/imageView" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_owner_main.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_owner3">
+
+	<TextView
+		android:id="@+id/textView"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_recovered_shards"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<TextView
+		android:id="@+id/textViewShardCount"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="0"
+		android:textSize="24sp"
+		app:layout_constraintTop_toBottomOf="@+id/textView"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<Button
+		android:id="@+id/button"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:text="@string/recovery_scan_qr_code"
+		app:layout_constraintBottom_toBottomOf="parent"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintHorizontal_bias="0.0"
+		app:layout_constraintStart_toStartOf="parent" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_recovery_owner_recovering.xml

@@ -0,0 +1,58 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:ignore="VectorDrawableCompat"
+	tools:showIn="@layout/activity_preview_recovery_owner4">
+
+	<TextView
+		android:id="@+id/textView"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_recovered_shards"
+		android:textSize="24sp"
+		app:layout_constraintTop_toTopOf="parent"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<TextView
+		android:id="@+id/textViewShardCount"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="3"
+		android:textSize="24sp"
+		app:layout_constraintTop_toBottomOf="@+id/textView"
+		tools:layout_editor_absoluteX="16dp" />
+
+	<ProgressBar
+		android:id="@+id/progressBar"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_gravity="center"
+		android:layout_marginTop="144dp"
+		android:indeterminate="true"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/textViewShardCount" />
+
+	<TextView
+		android:id="@+id/textView3"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:layout_marginTop="24dp"
+		android:gravity="center"
+		android:text="@string/recovery_recovering_account"
+		android:textSize="24sp"
+		app:layout_constraintTop_toBottomOf="@+id/progressBar" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_select_threshold.xml

@@ -0,0 +1,69 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/linearLayout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingLeft="@dimen/margin_large"
+    android:paddingTop="@dimen/margin_medium"
+    android:paddingRight="@dimen/margin_large"
+    android:paddingBottom="@dimen/margin_medium">
+
+    <TextView
+        android:id="@+id/title_threshold"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:text="@string/threshold"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <SeekBar
+        android:id="@+id/seekBar"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="8dp"
+        android:max="5"
+        android:paddingTop="10dp"
+        android:progress="3"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintHorizontal_bias="0.0"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/title_threshold" />
+
+
+    <TextView
+        android:id="@+id/textViewThresholdRepresentation"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="24dp"
+        android:text="placeholder"
+        android:textSize="64dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/seekBar" />
+
+    <TextView
+        android:id="@+id/textViewmOfn"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="24dp"
+        android:text="m of n contacts needed to recover your account"
+        android:textSize="16dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/textViewThresholdRepresentation" />
+
+    <TextView
+        android:id="@+id/textViewMessage"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="24dp"
+        android:text="@string/threshold_secure"
+        android:textSize="16dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/textViewmOfn" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_shards_received.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/linearLayout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingLeft="@dimen/margin_large"
+    android:paddingTop="@dimen/margin_medium"
+    android:paddingRight="@dimen/margin_large"
+    android:paddingBottom="@dimen/margin_medium">
+
+    <Button
+        android:id="@+id/button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="32dp"
+        android:text="@string/backup_done_dismiss"
+        android:textSize="24sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/textView2" />
+
+    <TextView
+        android:id="@+id/textView2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="16dp"
+        android:gravity="center"
+        android:text="@string/recovery_shard_received"
+        android:textSize="30sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/imageView2" />
+
+    <ImageView
+        android:id="@+id/imageView2"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_marginStart="32dp"
+        android:layout_marginLeft="32dp"
+        android:layout_marginTop="8dp"
+        android:layout_marginEnd="32dp"
+        android:layout_marginRight="32dp"
+        app:layout_constraintDimensionRatio="1:1"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:srcCompat="@drawable/ic_baseline_done_outline_24" />
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_shards_sent.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/linearLayout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingLeft="@dimen/margin_large"
+    android:paddingTop="@dimen/margin_medium"
+    android:paddingRight="@dimen/margin_large"
+    android:paddingBottom="@dimen/margin_medium">
+
+    <Button
+        android:id="@+id/button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="32dp"
+        android:text="@string/backup_done_dismiss"
+        android:textSize="24sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/textView2" />
+
+    <TextView
+        android:id="@+id/textView2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="16dp"
+        android:text="@string/backup_done_info"
+        android:gravity="center"
+        android:textSize="30sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/imageView2" />
+
+    <ImageView
+        android:id="@+id/imageView2"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_marginStart="32dp"
+        android:layout_marginLeft="32dp"
+        android:layout_marginTop="8dp"
+        android:layout_marginEnd="32dp"
+        android:layout_marginRight="32dp"
+        app:layout_constraintDimensionRatio="1:1"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:srcCompat="@drawable/ic_baseline_done_outline_24" />
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/fragment_start.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/linearLayout"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:paddingLeft="@dimen/margin_large"
+	android:paddingTop="@dimen/margin_medium"
+	android:paddingRight="@dimen/margin_large"
+	android:paddingBottom="@dimen/margin_medium"
+	tools:showIn="@layout/activity_preview_welcome">
+
+	<Button
+		android:id="@+id/buttonSelectThreshold"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:drawableLeft="@drawable/ic_contacts"
+		android:text="@string/setup_new_account"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent" />
+
+	<Button
+		android:id="@+id/buttonShardsSent"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:drawableLeft="@drawable/ic_repeat"
+		android:text="@string/setup_restore_account"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toBottomOf="@+id/buttonSelectThreshold" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

briar-android/src/main/res/layout/item_custodian.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    xmlns:tools="http://schemas.android.com/tools">
+
+    <CheckBox
+        android:id="@+id/checkBox"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Bob"
+        tools:text="@sample/names.json/names/short_names/name" />
+
+</LinearLayout>

briar-android/src/main/res/menu/conversation_actions.xml

@@ -27,4 +27,9 @@
 		android:title="@string/delete_contact"
 		app:showAsAction="never"/>
 
+	<item
+		android:id="@+id/action_help_recover_account"
+		android:icon="@drawable/introduction_white"
+		android:title="@string/help_recover_account"
+		app:showAsAction="never"/>
 </menu>

briar-android/src/main/res/menu/define_threshold_actions.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto">
+
+	<item
+		android:id="@+id/action_threshold_defined"
+		android:icon="@drawable/ic_check_white"
+		android:title="@string/threshold_defined"
+		app:showAsAction="always"/>
+
+</menu>

briar-android/src/main/res/values/strings.xml

@@ -456,7 +456,7 @@
 	<!-- Settings Profile Picture -->
 	<string name="change_profile_picture">Tap to change your profile picture</string>
 	<string name="dialog_confirm_profile_picture_title">Change profile picture</string>
-	<string name="dialog_confirm_profile_picture_remark">Only your contacts can see your profile image</string>
+	<string name="dialog_confirm_profile_picture_remark">Only your contacts can see this picture</string>
 	<string name="change_profile_picture_failed_message">We\'re sorry, but something went wrong while updating your profile picture</string>
 
 	<!-- Settings Display -->
@@ -638,4 +638,79 @@
 	<!-- This is a message to be used in screenshots. -->
 	<string name="screenshot_message_3">No problem, hope you like it 😀</string>
 
+	<!-- social backup -->
+
+	<!-- settings -->
+
+	<string name="pref_distributed_backup_title">Social backup</string>
+	<string name="pref_distributed_backup_summary">Backup your account using trusted contacts</string>
+
+	<string name="pref_distributed_old_backup_title">Existing Social backup</string>
+	<string name="pref_distributed_old_backup_summary">Information about your most recent social backup</string>
+
+	<!-- social backup procedure -->
+
+	<string name="select_custodians">Select Trusted Contacts:</string>
+
+	<string name="select_at_least_n_contacts">Please select at least %d contacts</string>
+	<string name="select_at_least_n_more_contacts">Please select at least %d more contacts</string>
+
+	<string name="threshold">The minimum number of trusted contacts needed to restore your account:</string>
+	<string name="threshold_secure">Secure</string>
+	<string name="threshold_recommended">Secure - recommended threshold</string>
+	<string name="threshold_low_insecure">Insecure – higher threshold recommended</string>
+	<string name="threshold_high_insecure">Danger of loss – lower threshold recommended</string>
+	<string name="threshold_defined">Choose Threshold</string>
+
+	<string name="backup_done_info">Backup pieces sent to trusted contacts</string>
+	<string name="backup_done_dismiss">Got it</string>
+
+	<string name="backup_created">Backup created 1/6/2020</string>
+
+	<!-- recovery from the secret owner's POV -->
+
+	<string name="recovery_explainer">You need to meet your trusted contacts in-person to receive pieces by scanning QR codes</string>
+	<string name="recovery_begin">Begin</string>
+	<string name="recovery_failed_to_receive">Failed to receive backup piece</string>
+	<string name="recovery_helpful_suggestions">Please check that bluetooth is swtiched on and that no-one but your trusted contact is able to scan the QR code</string>
+	<string name="recovery_retry">Retry</string>
+	<string name="recovery_recovered_shards">Recovered backup pieces:</string>
+	<string name="recovery_scan_qr_code">Scan QR code</string>
+	<string name="recovery_recovering_account">Recovering account…</string>
+	<string name="recovery_shard_received">Account backup piece received</string>
+	<string name="recovery_account_recovered">Account recovered</string>
+
+	<!-- recovery from the custodian's POV -->
+
+	<string name="custodian_recovery_explainer">You need to meet in-person to transfer backup piece</string>
+	<string name="custodian_recovery_failed_to_send">Failed to send backup piece</string>
+	<string name="custodian_scan_code">Scan code</string>
+	<string name="custodian_shard_sent">Account backup piece transmitted</string>
+
+	<!-- titles for the app bar -->
+
+	<string name="title_distributed_backup">Social Backup</string>
+	<string name="title_select_custodians">Select Trusted Contacts</string>
+	<string name="title_define_threshold">Choose Threshold</string>
+	<string name="title_recovery_mode">Recovery Mode</string>
+	<string name="title_help_recover">Help recover account</string>
+
+	<!-- conversation action for custodian -->
+
+	<string name="help_recover_account">Help recover account</string>
+
+	<!-- setup screen -->
+
+	<string name="setup_new_account">Create new account</string>
+	<string name="setup_restore_account">Restore account from backup</string>
+
+	<!-- Symbols for visualising threshold values for social backup -->
+	<string name="filled_bullet">\u25CF</string>
+    <string name="linear_bullet">\u25CB</string>
+
+	<!-- activity names -->
+	<string name="activity_name_distributed_backup">Social Backup</string>
+	<string name="activity_name_old_distributed_backup">Old Social Backup</string>
+
+	<string name="activity_name_new_or_recover_account">Create new account or recover existing account</string>
 </resources>

briar-android/src/main/res/xml/settings.xml

@@ -90,6 +90,17 @@
 		android:layout="@layout/preferences_category"
 		android:title="@string/security_settings_title">
 
+		<Preference
+			android:summary="@string/pref_distributed_backup_summary"
+			android:title="@string/pref_distributed_backup_title"
+			app:iconSpaceReserved="false">
+
+			<intent
+				android:targetClass="org.briarproject.briar.android.socialbackup.DistributedBackupActivity"
+				android:targetPackage="@string/app_package" />
+
+		</Preference>
+
 		<SwitchPreference
 			android:enabled="false"
 			android:key="pref_key_lock"

briar-android/witness.gradle

@@ -110,28 +110,32 @@ dependencyVerification {
         'com.google.auto:auto-common:0.8:auto-common-0.8.jar:97db1709f57b91b32edacb596ef4641872f227b7d99ad90e467f0d77f5ba134a',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.code.gson:gson:2.8.5:gson-2.8.5.jar:233a0149fc365c9f6edbd683cfe266b19bdc773be98eabdaf6b3c924b48e7d81',
+        'com.google.code.gson:gson:2.8.6:gson-2.8.6.jar:c8fb4839054d280b3033f800d1f5a97de2f028eb8ba2eb458ad287e536f3f25f',
         'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
         'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
         'com.google.dagger:dagger-spi:2.24:dagger-spi-2.24.jar:c038445d14dbcb4054e61bf49e05009edf26fce4fdc7ec1a9db544784f68e718',
         'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'com.google.errorprone:error_prone_annotations:2.2.0:error_prone_annotations-2.2.0.jar:6ebd22ca1b9d8ec06d41de8d64e0596981d9607b42035f9ed374f9de271a481a',
         'com.google.errorprone:error_prone_annotations:2.3.2:error_prone_annotations-2.3.2.jar:357cd6cfb067c969226c442451502aee13800a24e950fdfde77bcdb4565a668d',
+        'com.google.errorprone:error_prone_annotations:2.3.4:error_prone_annotations-2.3.4.jar:baf7d6ea97ce606c53e11b6854ba5f2ce7ef5c24dddf0afa18d1260bd25b002c',
         'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
         'com.google.googlejavaformat:google-java-format:1.5:google-java-format-1.5.jar:aa19ad7850fb85178aa22f2fddb163b84d6ce4d0035872f30d4408195ca1144e',
         'com.google.guava:failureaccess:1.0.1:failureaccess-1.0.1.jar:a171ee4c734dd2da837e4b16be9df4661afab72a41adaf31eb84dfdaf936ca26',
-        'com.google.guava:guava:27.0.1-jre:guava-27.0.1-jre.jar:e1c814fd04492a27c38e0317eabeaa1b3e950ec8010239e400fe90ad6c9107b4',
         'com.google.guava:guava:27.1-jre:guava-27.1-jre.jar:4a5aa70cc968a4d137e599ad37553e5cfeed2265e8c193476d7119036c536fe7',
+        'com.google.guava:guava:28.1-android:guava-28.1-android.jar:e112ce92c0f0733965eede73d94589c59a72128b06b08bba5ebe2f9ea672ef60',
         'com.google.guava:guava:28.1-jre:guava-28.1-jre.jar:30beb8b8527bd07c6e747e77f1a92122c2f29d57ce347461a4a55eb26e382da4',
         'com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava:listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar:b372a037d4230aa57fbeffdef30fd6123f9c0c2db85d0aced00c91b974f33f99',
         'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:2994a7eb78f2710bd3d3bfb639b2c94e219cedac0d4d084d516e78c16dddecf6',
         'com.google.j2objc:j2objc-annotations:1.3:j2objc-annotations-1.3.jar:21af30c92267bd6122c0e0b4d20cccb6641a37eaf956c6540ec471d584e64a7b',
         'com.google.jimfs:jimfs:1.1:jimfs-1.1.jar:c4828e28d7c0a930af9387510b3bada7daa5c04d7c25a75c7b8b081f1c257ddd',
-        'com.google.protobuf:protobuf-java:2.6.1:protobuf-java-2.6.1.jar:55aa554843983f431df5616112cf688d38aa17c132357afd1c109435bfdac4e6',
+        'com.google.protobuf:protobuf-java-util:3.11.4:protobuf-java-util-3.11.4.jar:29aacfff1cc455102627d4cfe6f319e4864ea7ce1a4e9d03b4c7bb01fc8255b0',
         'com.google.protobuf:protobuf-java:3.10.0:protobuf-java-3.10.0.jar:161d7d61a8cb3970891c299578702fd079646e032329d6c2cabf998d191437c9',
+        'com.google.protobuf:protobuf-java:3.11.4:protobuf-java-3.11.4.jar:42e98f58f53d1a49fd734c2dd193880f2dfec3436a2993a00d06b8800a22a3f2',
         'com.google.zxing:core:3.3.3:core-3.3.3.jar:5820f81e943e4bce0329306621e2d6255d2930b0a6ce934c5c23c0d6d3f20599',
         'com.googlecode.json-simple:json-simple:1.1:json-simple-1.1.jar:2d9484f4c649f708f47f9a479465fc729770ee65617dca3011836602264f6439',
         'com.ibm.icu:icu4j:53.1:icu4j-53.1.jar:e37a4467bac5cdeb02c5c4b8e5063d2f4e67b69e3c7df6d6b610f13185572bab',
         'com.jraska:falcon:2.1.1:falcon-2.1.1.aar:827f06556b7fa599f29a48a5277df39ca3dce5080d4ea6f9ea1f9c7b6b78bb7a',
+        'com.madgag.spongycastle:core:1.58.0.0:core-1.58.0.0.jar:199617dd5698c5a9312b898c0a4cec7ce9dd8649d07f65d91629f58229d72728',
         'com.squareup:javapoet:1.11.1:javapoet-1.11.1.jar:9cbf2107be499ec6e95afd36b58e3ca122a24166cdd375732e51267d64058e90',
         'com.squareup:javawriter:2.1.1:javawriter-2.1.1.jar:f699823d0081f69cbb676c1845ea222e0ada79bc88a53e5d22d8bd02d328f57e',
         'com.squareup:javawriter:2.5.0:javawriter-2.5.0.jar:fcfb09fb0ea0aa97d3cfe7ea792398081348e468f126b3603cb3803f240197f0',
@@ -156,6 +160,8 @@ dependencyVerification {
         'nekohtml:xercesMinimal:1.9.6.2:xercesMinimal-1.9.6.2.jar:95b8b357d19f63797dd7d67622fd3f18374d64acbc6584faba1c7759a31e8438',
         'net.bytebuddy:byte-buddy-agent:1.9.10:byte-buddy-agent-1.9.10.jar:8ed739d29132103250d307d2e8e3c95f07588ef0543ab11d2881d00768a5e182',
         'net.bytebuddy:byte-buddy:1.9.10:byte-buddy-1.9.10.jar:2936debc4d7b6c534848d361412e2d0f8bd06f7f27a6f4e728a20e97648d2bf3',
+        'net.i2p.crypto:eddsa:0.2.0:eddsa-0.2.0.jar:a7cb1b85c16e2f0730b9204106929a1d9aaae1df728adc7041a8b8b605692140',
+        'net.java.dev.jna:jna:5.5.0:jna-5.5.0.aar:12ef4a3c2ea685c9c816caa6a77ae8f17bb7727d8460f249925409acda270101',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
         'net.sf.jopt-simple:jopt-simple:4.9:jopt-simple-4.9.jar:26c5856e954b5f864db76f13b86919b59c6eecf9fd930b96baa8884626baf2f5',
         'net.sf.kxml:kxml2:2.3.0:kxml2-2.3.0.jar:f264dd9f79a1fde10ce5ecc53221eff24be4c9331c830b7d52f2f08a7b633de2',
@@ -184,6 +190,7 @@ dependencyVerification {
         'org.bouncycastle:bcprov-jdk15on:1.52:bcprov-jdk15on-1.52.jar:0dc4d181e4d347893c2ddbd2e6cd5d7287fc651c03648fa64b2341c7366b1773',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
+        'org.checkerframework:checker-compat-qual:2.5.5:checker-compat-qual-2.5.5.jar:11d134b245e9cacc474514d2d66b5b8618f8039a1465cdc55bbc0b34e0008b7a',
         'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
         'org.checkerframework:checker-qual:2.8.1:checker-qual-2.8.1.jar:9103499008bcecd4e948da29b17864abb64304e15706444ae209d17ebe0575df',
         'org.codehaus.groovy:groovy-all:2.4.15:groovy-all-2.4.15.jar:51d6c4e71782e85674239189499854359d380fb75e1a703756e3aaa5b98a5af0',
@@ -213,6 +220,9 @@ dependencyVerification {
         'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
         'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
         'org.jvnet.staxex:stax-ex:1.8:stax-ex-1.8.jar:95b05d9590af4154c6513b9c5dc1fb2e55b539972ba0a9ef28e9a0c01d83ad77',
+        'org.magmacollective.darkcrystal:dark-crystal-key-backup-crypto:1.0.0:dark-crystal-key-backup-crypto-1.0.0.jar:7c808f30314f7bc0c715b53415b07bd7e9a6bbcc55e5f672a296e5298d335f78',
+        'org.magmacollective.darkcrystal:dark-crystal-secret-sharing-wrapper:1.1.0:dark-crystal-secret-sharing-wrapper-1.1.0.aar:b8cac2348b9e652de413fa587168e9bb6ff36f6eea4bd1c72d3ecd56fc186e09',
+        'org.magmacollective.darkcrystal:shamir-secret-sharing-jna:1.0.0:shamir-secret-sharing-jna-1.0.0.aar:cdccfaf74dc1fcf30799a45d034c406315ce8507a8f4382eee118a66fb229ced',
         'org.mockito:mockito-core:3.1.0:mockito-core-3.1.0.jar:89b09e518e04f5c35f5ccf7abe45e72f594070a53d95cc2579001bd392c5afa6',
         'org.objenesis:objenesis:2.6:objenesis-2.6.jar:5e168368fbc250af3c79aa5fef0c3467a2d64e5a7bd74005f25d8399aeb0708d',
         'org.ow2.asm:asm-analysis:7.0:asm-analysis-7.0.jar:e981f8f650c4d900bb033650b18e122fa6b161eadd5f88978d08751f72ee8474',
@@ -231,6 +241,7 @@ dependencyVerification {
         'org.robolectric:shadows-framework:4.3.1:shadows-framework-4.3.1.jar:9c69db134cdd79be751856a148020fd9b32b086bb491846eedc0a1106fcadd5e',
         'org.robolectric:utils-reflector:4.3.1:utils-reflector-4.3.1.jar:9d7bf2557947d44d6f3ed76ec5231e8b72e33eb61c65ac9e149ad307b0eb936c',
         'org.robolectric:utils:4.3.1:utils-4.3.1.jar:6f9e406cd667019a5450e473c4e2d372bff9c9ab6ef55aafcbc9843109cb1519',
+        'org.whispersystems:curve25519-java:0.5.0:curve25519-java-0.5.0.jar:0aadd43cf01d11e9b58f867b3c4f25c3194e8b0623d1953d32dfbfbee009e38d',
         'tools.fastlane:screengrab:2.0.0:screengrab-2.0.0.aar:15ac15eb7c371db05e721be8d466567c2b7274b767d91478e781b6d89ee5d3d0',
         'uk.co.samuelwall:material-tap-target-prompt:3.0.0:material-tap-target-prompt-3.0.0.aar:e4d3c472b2d378e39a6535b7788e6c790fc9dde2d7659974e006ed8c7260911d',
     ]

briar-api/src/main/java/org/briarproject/briar/api/socialbackup/BackupExistsException.java

@@ -0,0 +1,11 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.db.DbException;
+
+/**
+ * Thrown when an attempt is made to create a social account backup but a
+ * backup already exists. This exception may occur due to concurrent updates
+ * and does not indicate a database error.
+ */
+public class BackupExistsException extends DbException {
+}

briar-api/src/main/java/org/briarproject/briar/api/socialbackup/BackupMetadata.java

@@ -0,0 +1,42 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class BackupMetadata {
+
+	private final SecretKey secret;
+	private final List<Author> custodians;
+	private final int threshold, version;
+
+	public BackupMetadata(SecretKey secret, List<Author> custodians,
+			int threshold, int version) {
+		this.secret = secret;
+		this.custodians = custodians;
+		this.threshold = threshold;
+		this.version = version;
+	}
+
+	public SecretKey getSecret() {
+		return secret;
+	}
+
+	public List<Author> getCustodians() {
+		return custodians;
+	}
+
+	public int getThreshold() {
+		return threshold;
+	}
+
+	public int getVersion() {
+		return version;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/socialbackup/DarkCrystal.java

@@ -0,0 +1,15 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.security.GeneralSecurityException;
+import java.util.List;
+
+@NotNullByDefault
+public
+interface DarkCrystal {
+
+	List<Shard> createShards(SecretKey secret, int shards, int threshold);
+	SecretKey combineShards(List<Shard> shards) throws GeneralSecurityException;
+}

briar-api/src/main/java/org/briarproject/briar/api/socialbackup/Shard.java

@@ -0,0 +1,25 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class Shard {
+
+	private final byte[] secretId, shard;
+
+	public Shard(byte[] secretId, byte[] shard) {
+		this.secretId = secretId;
+		this.shard = shard;
+	}
+
+	public byte[] getSecretId() {
+		return secretId;
+	}
+
+	public byte[] getShard() {
+		return shard;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/socialbackup/SocialBackupManager.java

@@ -0,0 +1,47 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+
+import java.util.List;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface SocialBackupManager {
+
+	/**
+	 * The unique ID of the social backup client.
+	 */
+	ClientId CLIENT_ID = new ClientId("pw.darkcrystal.backup");
+
+	/**
+	 * The current major version of the social backup client.
+	 */
+	int MAJOR_VERSION = 0;
+
+	/**
+	 * The current minor version of the social backup client.
+	 */
+	int MINOR_VERSION = 0;
+
+	/**
+	 * Returns the metadata for this device's backup, or null if no backup has
+	 * been created.
+	 */
+	@Nullable
+	BackupMetadata getBackupMetadata(Transaction txn) throws DbException;
+
+	/**
+	 * Creates a backup for this device using the given custodians and
+	 * threshold. The encrypted backup and a shard of the backup key will be
+	 * sent to each custodian.
+	 *
+	 * @throws BackupExistsException If a backup already exists
+	 */
+	void createBackup(Transaction txn, List<ContactId> custodianIds,
+			int threshold) throws DbException;
+}

briar-core/src/main/java/org/briarproject/briar/BriarCoreEagerSingletons.java

@@ -10,6 +10,7 @@ import org.briarproject.briar.messaging.MessagingModule;
 import org.briarproject.briar.privategroup.PrivateGroupModule;
 import org.briarproject.briar.privategroup.invitation.GroupInvitationModule;
 import org.briarproject.briar.sharing.SharingModule;
+import org.briarproject.briar.socialbackup.SocialBackupModule;
 
 public interface BriarCoreEagerSingletons {
 
@@ -33,6 +34,8 @@ public interface BriarCoreEagerSingletons {
 
 	void inject(SharingModule.EagerSingletons init);
 
+	void inject(SocialBackupModule.EagerSingletons init);
+
 	class Helper {
 
 		public static void injectEagerSingletons(BriarCoreEagerSingletons c) {
@@ -46,6 +49,7 @@ public interface BriarCoreEagerSingletons {
 			c.inject(new SharingModule.EagerSingletons());
 			c.inject(new IdentityModule.EagerSingletons());
 			c.inject(new IntroductionModule.EagerSingletons());
+			c.inject(new SocialBackupModule.EagerSingletons());
 		}
 	}
 }

briar-core/src/main/java/org/briarproject/briar/BriarCoreModule.java

@@ -13,6 +13,7 @@ import org.briarproject.briar.messaging.MessagingModule;
 import org.briarproject.briar.privategroup.PrivateGroupModule;
 import org.briarproject.briar.privategroup.invitation.GroupInvitationModule;
 import org.briarproject.briar.sharing.SharingModule;
+import org.briarproject.briar.socialbackup.SocialBackupModule;
 import org.briarproject.briar.test.TestModule;
 
 import dagger.Module;
@@ -31,6 +32,7 @@ import dagger.Module;
 		MessagingModule.class,
 		PrivateGroupModule.class,
 		SharingModule.class,
+		SocialBackupModule.class,
 		TestModule.class
 })
 public class BriarCoreModule {

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupMetadataEncoder.java

@@ -0,0 +1,11 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+
+@NotNullByDefault
+interface BackupMetadataEncoder {
+
+	BdfDictionary encodeBackupMetadata(BackupMetadata backupMetadata);
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupMetadataEncoderImpl.java

@@ -0,0 +1,42 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_CUSTODIANS;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_SECRET;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_THRESHOLD;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_VERSION;
+
+@Immutable
+@NotNullByDefault
+class BackupMetadataEncoderImpl implements BackupMetadataEncoder {
+
+	private final ClientHelper clientHelper;
+
+	@Inject
+	BackupMetadataEncoderImpl(ClientHelper clientHelper) {
+		this.clientHelper = clientHelper;
+	}
+
+	@Override
+	public BdfDictionary encodeBackupMetadata(BackupMetadata backupMetadata) {
+		BdfList custodians = new BdfList();
+		for (Author custodian : backupMetadata.getCustodians()) {
+			custodians.add(clientHelper.toList(custodian));
+		}
+		BdfDictionary meta = new BdfDictionary();
+		meta.put(GROUP_KEY_SECRET, backupMetadata.getSecret().getBytes());
+		meta.put(GROUP_KEY_CUSTODIANS, custodians);
+		meta.put(GROUP_KEY_THRESHOLD, backupMetadata.getThreshold());
+		meta.put(GROUP_KEY_VERSION, backupMetadata.getVersion());
+		return meta;
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupMetadataParser.java

@@ -0,0 +1,16 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+interface BackupMetadataParser {
+
+	@Nullable
+	BackupMetadata parseBackupMetadata(BdfDictionary meta)
+			throws FormatException;
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupMetadataParserImpl.java

@@ -0,0 +1,51 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_CUSTODIANS;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_SECRET;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_THRESHOLD;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_VERSION;
+
+@Immutable
+@NotNullByDefault
+class BackupMetadataParserImpl implements BackupMetadataParser {
+
+	private final ClientHelper clientHelper;
+
+	@Inject
+	BackupMetadataParserImpl(ClientHelper clientHelper) {
+		this.clientHelper = clientHelper;
+	}
+
+	@Nullable
+	@Override
+	public BackupMetadata parseBackupMetadata(BdfDictionary meta)
+			throws FormatException {
+		if (meta.isEmpty()) return null;
+		SecretKey secret = new SecretKey(meta.getRaw(GROUP_KEY_SECRET));
+		BdfList bdfCustodians = meta.getList(GROUP_KEY_CUSTODIANS);
+		List<Author> custodians = new ArrayList<>(bdfCustodians.size());
+		for (int i = 0; i < bdfCustodians.size(); i++) {
+			BdfList author = bdfCustodians.getList(i);
+			custodians.add(clientHelper.parseAndValidateAuthor(author));
+		}
+		int threshold = meta.getLong(GROUP_KEY_THRESHOLD).intValue();
+		int version = meta.getLong(GROUP_KEY_VERSION).intValue();
+		return new BackupMetadata(secret, custodians, threshold, version);
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupPayload.java

@@ -0,0 +1,15 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.Bytes;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+class BackupPayload extends Bytes {
+
+	BackupPayload(byte[] payload) {
+		super(payload);
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupPayloadEncoder.java

@@ -0,0 +1,14 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.identity.Identity;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+@NotNullByDefault
+interface BackupPayloadEncoder {
+
+	BackupPayload encodeBackupPayload(SecretKey secret, Identity identity,
+			List<ContactData> contactData, int version);
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/BackupPayloadEncoderImpl.java

@@ -0,0 +1,91 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.crypto.AuthenticatedCipher;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.identity.Identity;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+import java.security.GeneralSecurityException;
+import java.security.SecureRandom;
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+import javax.inject.Provider;
+
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.AUTH_TAG_BYTES;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.NONCE_BYTES;
+
+@Immutable
+@NotNullByDefault
+class BackupPayloadEncoderImpl implements BackupPayloadEncoder {
+
+	private final ClientHelper clientHelper;
+	private final Provider<AuthenticatedCipher> cipherProvider;
+	private final SecureRandom secureRandom;
+	private final MessageEncoder messageEncoder;
+
+	@Inject
+	BackupPayloadEncoderImpl(ClientHelper clientHelper,
+			Provider<AuthenticatedCipher> cipherProvider,
+			SecureRandom secureRandom,
+			MessageEncoder messageEncoder) {
+		this.clientHelper = clientHelper;
+		this.cipherProvider = cipherProvider;
+		this.secureRandom = secureRandom;
+		this.messageEncoder = messageEncoder;
+	}
+
+	@Override
+	public BackupPayload encodeBackupPayload(SecretKey secret,
+			Identity identity, List<ContactData> contactData, int version) {
+		// Encode the local identity
+		BdfList bdfIdentity = new BdfList();
+		LocalAuthor localAuthor = identity.getLocalAuthor();
+		bdfIdentity.add(clientHelper.toList(localAuthor));
+		bdfIdentity.add(localAuthor.getPrivateKey().getEncoded());
+		bdfIdentity.add(identity.getHandshakePublicKey().getEncoded());
+		bdfIdentity.add(identity.getHandshakePrivateKey().getEncoded());
+		// Encode the contact data
+		BdfList bdfContactData = new BdfList();
+		for (ContactData cd : contactData) {
+			BdfList bdfData = new BdfList();
+			Contact contact = cd.getContact();
+			bdfData.add(clientHelper.toList(contact.getAuthor()));
+			bdfData.add(contact.getAlias());
+			PublicKey pub = contact.getHandshakePublicKey();
+			bdfData.add(pub == null ? null : pub.getEncoded());
+			bdfData.add(clientHelper.toDictionary(cd.getProperties()));
+			Shard shard = cd.getShard();
+			if (shard == null) bdfData.add(null);
+			else bdfData.add(messageEncoder.encodeShardMessage(shard));
+			bdfContactData.add(bdfData);
+		}
+		// Encode and encrypt the payload
+		BdfList backup = new BdfList();
+		backup.add(version);
+		backup.add(bdfIdentity);
+		backup.add(bdfContactData);
+		try {
+			byte[] plaintext = clientHelper.toByteArray(backup);
+			byte[] ciphertext = new byte[plaintext.length + AUTH_TAG_BYTES];
+			byte[] nonce = new byte[NONCE_BYTES];
+			secureRandom.nextBytes(nonce);
+			AuthenticatedCipher cipher = cipherProvider.get();
+			cipher.init(true, secret, nonce);
+			int encrypted = cipher.process(plaintext, 0, plaintext.length,
+					ciphertext, 0);
+			if (encrypted != ciphertext.length) throw new AssertionError();
+			return new BackupPayload(ciphertext);
+		} catch (FormatException | GeneralSecurityException e) {
+			throw new AssertionError(e);
+		}
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/ContactData.java

@@ -0,0 +1,43 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+import java.util.Map;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+class ContactData {
+
+	private final Contact contact;
+	private final Map<TransportId, TransportProperties> properties;
+	@Nullable
+	private final Shard shard;
+
+	ContactData(Contact contact,
+			Map<TransportId, TransportProperties> properties,
+			@Nullable Shard shard) {
+		this.contact = contact;
+		this.properties = properties;
+		this.shard = shard;
+	}
+
+	public Contact getContact() {
+		return contact;
+	}
+
+	public Map<TransportId, TransportProperties> getProperties() {
+		return properties;
+	}
+
+	@Nullable
+	public Shard getShard() {
+		return shard;
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/DarkCrystalStub.java

@@ -0,0 +1,54 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+import java.security.GeneralSecurityException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+
+import javax.inject.Inject;
+
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.SECRET_ID_BYTES;
+
+@NotNullByDefault
+class DarkCrystalStub implements DarkCrystal {
+
+	@Inject
+	DarkCrystalStub() {
+	}
+
+	@Override
+	public List<Shard> createShards(SecretKey secret, int numShards,
+			int threshold) {
+		Random random = new Random();
+		byte[] secretId = new byte[SECRET_ID_BYTES];
+		random.nextBytes(secretId);
+		List<Shard> shards = new ArrayList<>(numShards);
+		for (int i = 0; i < numShards; i++) {
+			byte[] shard = new byte[123];
+			random.nextBytes(shard);
+			shards.add(new Shard(secretId, shard));
+		}
+		return shards;
+	}
+
+    @Override
+	public SecretKey combineShards(List<Shard> shards) throws
+			GeneralSecurityException {
+		// Check each shard has the same secret Id
+		byte[] secretId = shards.get(0).getSecretId();
+		for (Shard shard : shards) {
+			if (!Arrays.equals(shard.getSecretId(), secretId)) throw new GeneralSecurityException();
+		}
+
+		Random random = new Random();
+		byte[] secretBytes = new byte[SecretKey.LENGTH];
+		random.nextBytes(secretId);
+		return new SecretKey(secretBytes);
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/MessageEncoder.java

@@ -0,0 +1,12 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+@NotNullByDefault
+interface MessageEncoder {
+
+	byte[] encodeShardMessage(Shard shard);
+
+	byte[] encodeBackupMessage(int version, BackupPayload payload);
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/MessageEncoderImpl.java

@@ -0,0 +1,53 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.briar.socialbackup.MessageType.BACKUP;
+import static org.briarproject.briar.socialbackup.MessageType.SHARD;
+
+@Immutable
+@NotNullByDefault
+class MessageEncoderImpl implements MessageEncoder {
+
+	private final ClientHelper clientHelper;
+
+	@Inject
+	MessageEncoderImpl(ClientHelper clientHelper) {
+		this.clientHelper = clientHelper;
+	}
+
+	@Override
+	public byte[] encodeShardMessage(Shard shard) {
+		BdfList body = BdfList.of(
+				SHARD.getValue(),
+				shard.getSecretId(),
+				shard.getShard()
+		);
+		return encodeBody(body);
+	}
+
+	@Override
+	public byte[] encodeBackupMessage(int version, BackupPayload payload) {
+		BdfList body = BdfList.of(
+				BACKUP.getValue(),
+				version,
+				payload.getBytes()
+		);
+		return encodeBody(body);
+	}
+
+	private byte[] encodeBody(BdfList body) {
+		try {
+			return clientHelper.toByteArray(body);
+		} catch (FormatException e) {
+			throw new AssertionError(e);
+		}
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/MessageParser.java

@@ -0,0 +1,14 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+@NotNullByDefault
+interface MessageParser {
+
+	Shard parseShardMessage(BdfList body) throws FormatException;
+
+	BackupPayload parseBackupMessage(BdfList body) throws FormatException;
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/MessageParserImpl.java

@@ -0,0 +1,33 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.socialbackup.Shard;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+@Immutable
+@NotNullByDefault
+class MessageParserImpl implements MessageParser {
+
+	@Inject
+	MessageParserImpl() {
+	}
+
+	@Override
+	public Shard parseShardMessage(BdfList body) throws FormatException {
+		// Message type, secret ID, shard
+		byte[] secretId = body.getRaw(1);
+		byte[] shard = body.getRaw(2);
+		return new Shard(secretId, shard);
+	}
+
+	@Override
+	public BackupPayload parseBackupMessage(BdfList body)
+			throws FormatException {
+		// Message type, backup payload
+		return new BackupPayload(body.getRaw(1));
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/MessageType.java

@@ -0,0 +1,28 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+enum MessageType {
+
+	SHARD(0), BACKUP(1);
+
+	private final int value;
+
+	MessageType(int value) {
+		this.value = value;
+	}
+
+	int getValue() {
+		return value;
+	}
+
+	static MessageType fromValue(int value) throws FormatException {
+		for (MessageType m : values()) if (m.value == value) return m;
+		throw new FormatException();
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/SocialBackupConstants.java

@@ -0,0 +1,36 @@
+package org.briarproject.briar.socialbackup;
+
+public interface SocialBackupConstants {
+
+	// Group metadata keys
+	String GROUP_KEY_CONTACT_ID = "contactId";
+	String GROUP_KEY_SECRET = "secret";
+	String GROUP_KEY_CUSTODIANS = "custodians";
+	String GROUP_KEY_THRESHOLD = "threshold";
+	String GROUP_KEY_VERSION = "version";
+
+	// Message metadata keys
+	String MSG_KEY_MESSAGE_TYPE = "messageType";
+	String MSG_KEY_LOCAL = "local";
+	String MSG_KEY_VERSION = "version";
+
+	/**
+	 * The length of the authenticated cipher's nonce in bytes.
+	 */
+	int NONCE_BYTES = 24;
+
+	/**
+	 * The length of the authenticated cipher's authentication tag in bytes.
+	 */
+	int AUTH_TAG_BYTES = 16;
+
+	/**
+	 * The length of the secret ID in bytes.
+	 */
+	int SECRET_ID_BYTES = 32;
+
+	/**
+	 * The maximum length of a shard in bytes.
+	 */
+	int MAX_SHARD_BYTES = 1024;
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/SocialBackupManagerImpl.java

@@ -0,0 +1,421 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.client.BdfIncomingMessageHook;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.client.ContactGroupFactory;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.contact.ContactManager.ContactHook;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataParser;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.NoSuchContactException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Identity;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.OpenDatabaseHook;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TorConstants;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Group.Visibility;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager.ClientVersioningHook;
+import org.briarproject.briar.api.socialbackup.BackupExistsException;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+import org.briarproject.briar.api.socialbackup.Shard;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import static java.util.Collections.singletonMap;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.briar.socialbackup.MessageType.BACKUP;
+import static org.briarproject.briar.socialbackup.MessageType.SHARD;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_CONTACT_ID;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.GROUP_KEY_VERSION;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_LOCAL;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_MESSAGE_TYPE;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_VERSION;
+
+@NotNullByDefault
+class SocialBackupManagerImpl extends BdfIncomingMessageHook
+		implements SocialBackupManager, OpenDatabaseHook, ContactHook,
+		ClientVersioningHook {
+
+	private final ClientVersioningManager clientVersioningManager;
+	private final TransportPropertyManager transportPropertyManager;
+	private final ContactGroupFactory contactGroupFactory;
+	private final BackupMetadataParser backupMetadataParser;
+	private final BackupMetadataEncoder backupMetadataEncoder;
+	private final BackupPayloadEncoder backupPayloadEncoder;
+	private final MessageParser messageParser;
+	private final MessageEncoder messageEncoder;
+	private final IdentityManager identityManager;
+	private final ContactManager contactManager;
+	private final CryptoComponent crypto;
+	private final DarkCrystal darkCrystal;
+	private final Clock clock;
+	private final Group localGroup;
+
+	@Inject
+	SocialBackupManagerImpl(
+			DatabaseComponent db,
+			ClientHelper clientHelper,
+			MetadataParser metadataParser,
+			ClientVersioningManager clientVersioningManager,
+			TransportPropertyManager transportPropertyManager,
+			ContactGroupFactory contactGroupFactory,
+			BackupMetadataParser backupMetadataParser,
+			BackupMetadataEncoder backupMetadataEncoder,
+			BackupPayloadEncoder backupPayloadEncoder,
+			MessageParser messageParser,
+			MessageEncoder messageEncoder,
+			IdentityManager identityManager,
+			ContactManager contactManager,
+			CryptoComponent crypto,
+			DarkCrystal darkCrystal,
+			Clock clock) {
+		super(db, clientHelper, metadataParser);
+		this.clientVersioningManager = clientVersioningManager;
+		this.transportPropertyManager = transportPropertyManager;
+		this.contactGroupFactory = contactGroupFactory;
+		this.backupMetadataParser = backupMetadataParser;
+		this.backupMetadataEncoder = backupMetadataEncoder;
+		this.backupPayloadEncoder = backupPayloadEncoder;
+		this.messageParser = messageParser;
+		this.messageEncoder = messageEncoder;
+		this.identityManager = identityManager;
+		this.contactManager = contactManager;
+		this.crypto = crypto;
+		this.darkCrystal = darkCrystal;
+		localGroup =
+				contactGroupFactory.createLocalGroup(CLIENT_ID, MAJOR_VERSION);
+		this.clock = clock;
+	}
+
+	@Override
+	public void onDatabaseOpened(Transaction txn) throws DbException {
+		if (db.containsGroup(txn, localGroup.getId())) return;
+		db.addGroup(txn, localGroup);
+		// Set things up for any pre-existing contacts
+		for (Contact c : db.getContacts(txn)) addingContact(txn, c);
+	}
+
+	@Override
+	public void addingContact(Transaction txn, Contact c) throws DbException {
+		// Create a group to share with the contact
+		Group g = getContactGroup(c);
+		db.addGroup(txn, g);
+		// Apply the client's visibility to the contact group
+		Visibility client = clientVersioningManager.getClientVisibility(txn,
+				c.getId(), CLIENT_ID, MAJOR_VERSION);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), client);
+		// Attach the contact ID to the group
+		setContactId(txn, g.getId(), c.getId());
+		// Add the contact to our backup, if any
+		if (localBackupExists(txn)) {
+			updateBackup(txn, loadContactData(txn));
+		}
+	}
+
+	@Override
+	public void removingContact(Transaction txn, Contact c) throws DbException {
+		db.removeGroup(txn, getContactGroup(c));
+		// Remove the contact from our backup, if any
+		if (localBackupExists(txn)) {
+			updateBackup(txn, loadContactData(txn));
+		}
+	}
+
+	@Override
+	public void onClientVisibilityChanging(Transaction txn, Contact c,
+			Visibility v) throws DbException {
+		// Apply the client's visibility to the contact group
+		Group g = getContactGroup(c);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), v);
+	}
+
+	@Override
+	protected boolean incomingMessage(Transaction txn, Message m, BdfList body,
+			BdfDictionary meta) throws DbException, FormatException {
+		MessageType type = MessageType.fromValue(body.getLong(0).intValue());
+		if (type == SHARD) {
+			// Only one shard should be received from each contact
+			if (findMessage(txn, m.getGroupId(), SHARD, false) != null) {
+				throw new FormatException();
+			}
+			// Add the shard to our backup, if any
+			if (localBackupExists(txn)) {
+				Shard shard = messageParser.parseShardMessage(body);
+				ContactId c = getContactId(txn, m.getGroupId());
+				List<ContactData> contactData = loadContactData(txn);
+				ListIterator<ContactData> it = contactData.listIterator();
+				while (it.hasNext()) {
+					ContactData cd = it.next();
+					if (cd.getContact().getId().equals(c)) {
+						it.set(new ContactData(cd.getContact(),
+								cd.getProperties(), shard));
+						updateBackup(txn, contactData);
+						break;
+					}
+				}
+			}
+		} else if (type == BACKUP) {
+			// Keep the newest version of the backup, delete any older versions
+			int version = meta.getLong(MSG_KEY_VERSION).intValue();
+			Pair<MessageId, BdfDictionary> prev =
+					findMessage(txn, m.getGroupId(), BACKUP, false);
+			if (prev != null) {
+				MessageId prevId = prev.getFirst();
+				BdfDictionary prevMeta = prev.getSecond();
+				int prevVersion = prevMeta.getLong(MSG_KEY_VERSION).intValue();
+				if (version > prevVersion) {
+					// This backup is newer - delete the previous backup
+					db.deleteMessage(txn, prevId);
+					db.deleteMessageMetadata(txn, prevId);
+				} else {
+					// We've already received a newer backup - delete this one
+					db.deleteMessage(txn, m.getId());
+					db.deleteMessageMetadata(txn, m.getId());
+				}
+			}
+		}
+		return false;
+	}
+
+	@Nullable
+	@Override
+	public BackupMetadata getBackupMetadata(Transaction txn)
+			throws DbException {
+		try {
+			BdfDictionary meta = clientHelper.getGroupMetadataAsDictionary(txn,
+					localGroup.getId());
+			return backupMetadataParser.parseBackupMetadata(meta);
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	@Override
+	public void createBackup(Transaction txn, List<ContactId> custodianIds,
+			int threshold) throws DbException {
+		if (localBackupExists(txn)) throw new BackupExistsException();
+		// Load the contacts
+		List<Contact> custodians = new ArrayList<>(custodianIds.size());
+		for (ContactId custodianId : custodianIds) {
+			custodians.add(contactManager.getContact(txn, custodianId));
+		}
+		// Create the encrypted backup payload
+		SecretKey secret = crypto.generateSecretKey();
+		List<ContactData> contactData = loadContactData(txn);
+		BackupPayload payload =
+				createBackupPayload(txn, secret, contactData, 0);
+		// Create the shards
+		List<Shard> shards = darkCrystal.createShards(secret,
+				custodians.size(), threshold);
+		try {
+			// Send the shard and backup messages to the custodians
+			for (int i = 0; i < custodians.size(); i++) {
+				Contact custodian = custodians.get(i);
+				Shard shard = shards.get(i);
+				sendShardMessage(txn, custodian, shard);
+				sendBackupMessage(txn, custodian, 0, payload);
+			}
+			// Store the backup metadata
+			List<Author> authors = new ArrayList<>(custodians.size());
+			for (Contact custodian : custodians) {
+				authors.add(custodian.getAuthor());
+			}
+			BackupMetadata backupMetadata =
+					new BackupMetadata(secret, authors, threshold, 0);
+			BdfDictionary meta =
+					backupMetadataEncoder.encodeBackupMetadata(backupMetadata);
+			clientHelper.mergeGroupMetadata(txn, localGroup.getId(), meta);
+		} catch (FormatException e) {
+			throw new AssertionError(e);
+		}
+	}
+
+	private Group getContactGroup(Contact c) {
+		return contactGroupFactory.createContactGroup(CLIENT_ID,
+				MAJOR_VERSION, c);
+	}
+
+	private void setContactId(Transaction txn, GroupId g, ContactId c)
+			throws DbException {
+		BdfDictionary d = new BdfDictionary();
+		d.put(GROUP_KEY_CONTACT_ID, c.getInt());
+		try {
+			clientHelper.mergeGroupMetadata(txn, g, d);
+		} catch (FormatException e) {
+			throw new AssertionError(e);
+		}
+	}
+
+	private ContactId getContactId(Transaction txn, GroupId g)
+			throws DbException {
+		try {
+			BdfDictionary meta =
+					clientHelper.getGroupMetadataAsDictionary(txn, g);
+			return new ContactId(meta.getLong(GROUP_KEY_CONTACT_ID).intValue());
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	private BackupPayload createBackupPayload(Transaction txn,
+			SecretKey secret, List<ContactData> contactData, int version)
+			throws DbException {
+		Identity identity = identityManager.getIdentity(txn);
+		return backupPayloadEncoder.encodeBackupPayload(secret, identity,
+				contactData, version);
+	}
+
+	private List<ContactData> loadContactData(Transaction txn)
+			throws DbException {
+		Collection<Contact> contacts = contactManager.getContacts(txn);
+		List<ContactData> contactData = new ArrayList<>();
+		for (Contact c : contacts) {
+			// Skip contacts that are in the process of being removed
+			Group contactGroup = getContactGroup(c);
+			if (!db.containsGroup(txn, contactGroup.getId())) continue;
+			Map<TransportId, TransportProperties> props =
+					getTransportProperties(txn, c.getId());
+			Shard shard = getRemoteShard(txn, contactGroup.getId());
+			contactData.add(new ContactData(c, props, shard));
+		}
+		return contactData;
+	}
+
+	private Map<TransportId, TransportProperties> getTransportProperties(
+			Transaction txn, ContactId c) throws DbException {
+		// TODO: Include filtered properties for other transports
+		TransportProperties p = transportPropertyManager
+				.getRemoteProperties(txn, c, TorConstants.ID);
+		return singletonMap(TorConstants.ID, p);
+	}
+
+	private void sendShardMessage(Transaction txn, Contact custodian,
+			Shard shard) throws DbException, FormatException {
+		GroupId g = getContactGroup(custodian).getId();
+		long timestamp = clock.currentTimeMillis();
+		byte[] body = messageEncoder.encodeShardMessage(shard);
+		Message m = clientHelper.createMessage(g, timestamp, body);
+		BdfDictionary meta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, SHARD.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		clientHelper.addLocalMessage(txn, m, meta, true, false);
+	}
+
+	private void sendBackupMessage(Transaction txn, Contact custodian,
+			int version, BackupPayload payload)
+			throws DbException, FormatException {
+		GroupId g = getContactGroup(custodian).getId();
+		long timestamp = clock.currentTimeMillis();
+		byte[] body = messageEncoder.encodeBackupMessage(version, payload);
+		Message m = clientHelper.createMessage(g, timestamp, body);
+		BdfDictionary meta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, BACKUP.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, true),
+				new BdfEntry(MSG_KEY_VERSION, version));
+		clientHelper.addLocalMessage(txn, m, meta, true, false);
+	}
+
+	private boolean localBackupExists(Transaction txn) throws DbException {
+		return !db.getGroupMetadata(txn, localGroup.getId()).isEmpty();
+	}
+
+	@Nullable
+	private Shard getRemoteShard(Transaction txn, GroupId g)
+			throws DbException {
+		try {
+			Pair<MessageId, BdfDictionary> prev =
+					findMessage(txn, g, SHARD, false);
+			if (prev == null) return null;
+			BdfList body = clientHelper.getMessageAsList(txn, prev.getFirst());
+			return messageParser.parseShardMessage(body);
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	private void updateBackup(Transaction txn, List<ContactData> contactData)
+			throws DbException {
+		BackupMetadata backupMetadata = requireNonNull(getBackupMetadata(txn));
+		int newVersion = backupMetadata.getVersion() + 1;
+		BackupPayload payload = createBackupPayload(txn,
+				backupMetadata.getSecret(), contactData, newVersion);
+		LocalAuthor localAuthor = identityManager.getLocalAuthor(txn);
+		try {
+			for (Author author : backupMetadata.getCustodians()) {
+				try {
+					Contact custodian = contactManager.getContact(txn,
+							author.getId(), localAuthor.getId());
+					Group contactGroup = getContactGroup(custodian);
+					Pair<MessageId, BdfDictionary> prev = findMessage(txn,
+							contactGroup.getId(), BACKUP, true);
+					if (prev != null) {
+						// Delete the previous backup message
+						MessageId prevId = prev.getFirst();
+						db.deleteMessage(txn, prevId);
+						db.deleteMessageMetadata(txn, prevId);
+					}
+					sendBackupMessage(txn, custodian, newVersion, payload);
+				} catch (NoSuchContactException e) {
+					// The custodian is no longer a contact - continue
+				}
+			}
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+		BdfDictionary meta =
+				BdfDictionary.of(new BdfEntry(GROUP_KEY_VERSION, newVersion));
+		try {
+			clientHelper.mergeGroupMetadata(txn, localGroup.getId(), meta);
+		} catch (FormatException e) {
+			throw new AssertionError(e);
+		}
+	}
+
+	@Nullable
+	private Pair<MessageId, BdfDictionary> findMessage(Transaction txn,
+			GroupId g, MessageType type, boolean local)
+			throws DbException, FormatException {
+		BdfDictionary query = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, type.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, local));
+		Map<MessageId, BdfDictionary> results =
+				clientHelper.getMessageMetadataAsDictionary(txn, g, query);
+		if (results.size() > 1) throw new DbException();
+		if (results.isEmpty()) return null;
+		Entry<MessageId, BdfDictionary> e =
+				results.entrySet().iterator().next();
+		return new Pair<>(e.getKey(), e.getValue());
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/SocialBackupModule.java

@@ -0,0 +1,97 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+import static org.briarproject.briar.api.socialbackup.SocialBackupManager.CLIENT_ID;
+import static org.briarproject.briar.api.socialbackup.SocialBackupManager.MAJOR_VERSION;
+import static org.briarproject.briar.api.socialbackup.SocialBackupManager.MINOR_VERSION;
+
+@Module
+public class SocialBackupModule {
+
+	public static class EagerSingletons {
+		@Inject
+		SocialBackupManager socialBackupManager;
+		@Inject
+		SocialBackupValidator socialBackupValidator;
+	}
+
+	@Provides
+	@Singleton
+	SocialBackupManager socialBackupManager(
+			LifecycleManager lifecycleManager,
+			ContactManager contactManager,
+			ValidationManager validationManager,
+			ClientVersioningManager clientVersioningManager,
+			SocialBackupManagerImpl socialBackupManager) {
+		lifecycleManager.registerOpenDatabaseHook(socialBackupManager);
+		contactManager.registerContactHook(socialBackupManager);
+		validationManager.registerIncomingMessageHook(CLIENT_ID,
+				MAJOR_VERSION, socialBackupManager);
+		clientVersioningManager.registerClient(CLIENT_ID, MAJOR_VERSION,
+				MINOR_VERSION, socialBackupManager);
+		return socialBackupManager;
+	}
+
+	@Provides
+	@Singleton
+	SocialBackupValidator socialBackupValidator(
+			ValidationManager validationManager,
+			ClientHelper clientHelper,
+			MetadataEncoder metadataEncoder,
+			Clock clock) {
+		SocialBackupValidator validator =
+				new SocialBackupValidator(clientHelper, metadataEncoder, clock);
+		validationManager.registerMessageValidator(CLIENT_ID, MAJOR_VERSION,
+				validator);
+		return validator;
+	}
+
+	@Provides
+	BackupMetadataParser backupMetadataParser(
+			BackupMetadataParserImpl backupMetadataParser) {
+		return backupMetadataParser;
+	}
+
+	@Provides
+	BackupMetadataEncoder backupMetadataEncoder(
+			BackupMetadataEncoderImpl backupMetadataEncoder) {
+		return backupMetadataEncoder;
+	}
+
+	@Provides
+	BackupPayloadEncoder backupPayloadEncoder(
+			BackupPayloadEncoderImpl backupPayloadEncoder) {
+		return backupPayloadEncoder;
+	}
+
+	@Provides
+	MessageEncoder messageEncoder(MessageEncoderImpl messageEncoder) {
+		return messageEncoder;
+	}
+
+	@Provides
+	MessageParser messageParser(MessageParserImpl messageParser) {
+		return messageParser;
+	}
+
+	@Provides
+	DarkCrystal darkCrystal(DarkCrystalStub darkCrystal) {
+		// TODO: Replace this with a real implementation
+		return darkCrystal;
+	}
+}

briar-core/src/main/java/org/briarproject/briar/socialbackup/SocialBackupValidator.java

@@ -0,0 +1,75 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.BdfMessageContext;
+import org.briarproject.bramble.api.client.BdfMessageValidator;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.system.Clock;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.util.ValidationUtils.checkLength;
+import static org.briarproject.bramble.util.ValidationUtils.checkSize;
+import static org.briarproject.briar.socialbackup.MessageType.BACKUP;
+import static org.briarproject.briar.socialbackup.MessageType.SHARD;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MAX_SHARD_BYTES;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_LOCAL;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_MESSAGE_TYPE;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_VERSION;
+import static org.briarproject.briar.socialbackup.SocialBackupConstants.SECRET_ID_BYTES;
+
+@Immutable
+@NotNullByDefault
+class SocialBackupValidator extends BdfMessageValidator {
+
+	@Inject
+	SocialBackupValidator(ClientHelper clientHelper,
+			MetadataEncoder metadataEncoder, Clock clock) {
+		super(clientHelper, metadataEncoder, clock);
+	}
+
+	@Override
+	protected BdfMessageContext validateMessage(Message m, Group g,
+			BdfList body) throws FormatException {
+		MessageType type = MessageType.fromValue(body.getLong(0).intValue());
+		if (type == SHARD) return validateShardMessage(body);
+		else if (type == BACKUP) return validateBackupMessage(body);
+		else throw new AssertionError();
+	}
+
+	private BdfMessageContext validateShardMessage(BdfList body)
+			throws FormatException {
+		// Message type, secret ID, shard
+		checkSize(body, 3);
+		byte[] secretId = body.getRaw(1);
+		checkLength(secretId, SECRET_ID_BYTES);
+		byte[] shard = body.getRaw(2);
+		checkLength(shard, 1, MAX_SHARD_BYTES);
+		BdfDictionary meta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, SHARD.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		return new BdfMessageContext(meta);
+	}
+
+	private BdfMessageContext validateBackupMessage(BdfList body)
+			throws FormatException {
+		// Message type, version, backup payload
+		checkSize(body, 3);
+		int version = body.getLong(1).intValue();
+		if (version < 0) throw new FormatException();
+		byte[] payload = body.getRaw(2);
+		BdfDictionary meta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, BACKUP.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, false),
+				new BdfEntry(MSG_KEY_VERSION, version));
+		return new BdfMessageContext(meta);
+	}
+}

briar-core/src/test/java/org/briarproject/briar/introduction/IntroductionIntegrationTestComponent.java

@@ -2,16 +2,7 @@ package org.briarproject.briar.introduction;
 
 import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
-import org.briarproject.briar.attachment.AttachmentModule;
-import org.briarproject.briar.avatar.AvatarModule;
-import org.briarproject.briar.blog.BlogModule;
-import org.briarproject.briar.client.BriarClientModule;
-import org.briarproject.briar.forum.ForumModule;
-import org.briarproject.briar.identity.IdentityModule;
-import org.briarproject.briar.messaging.MessagingModule;
-import org.briarproject.briar.privategroup.PrivateGroupModule;
-import org.briarproject.briar.privategroup.invitation.GroupInvitationModule;
-import org.briarproject.briar.sharing.SharingModule;
+import org.briarproject.briar.BriarCoreModule;
 import org.briarproject.briar.test.BriarIntegrationTestComponent;
 
 import javax.inject.Singleton;
@@ -22,17 +13,7 @@ import dagger.Component;
 @Component(modules = {
 		BrambleCoreIntegrationTestModule.class,
 		BrambleCoreModule.class,
-		AvatarModule.class,
-		BlogModule.class,
-		BriarClientModule.class,
-		ForumModule.class,
-		GroupInvitationModule.class,
-		IdentityModule.class,
-		IntroductionModule.class,
-		AttachmentModule.class,
-		MessagingModule.class,
-		PrivateGroupModule.class,
-		SharingModule.class
+		BriarCoreModule.class
 })
 interface IntroductionIntegrationTestComponent
 		extends BriarIntegrationTestComponent {

briar-core/src/test/java/org/briarproject/briar/socialbackup/SocialBackupIntegrationTest.java

@@ -0,0 +1,75 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.test.TestDatabaseConfigModule;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+import org.briarproject.briar.test.BriarIntegrationTest;
+import org.briarproject.briar.test.BriarIntegrationTestComponent;
+import org.briarproject.briar.test.DaggerBriarIntegrationTestComponent;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.List;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+public class SocialBackupIntegrationTest
+		extends BriarIntegrationTest<BriarIntegrationTestComponent> {
+
+	private SocialBackupManager socialBackupManager0;
+
+	@Before
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		socialBackupManager0 = c0.getSocialBackupManager();
+	}
+
+	@Override
+	protected void createComponents() {
+		BriarIntegrationTestComponent component =
+				DaggerBriarIntegrationTestComponent.builder().build();
+		BriarIntegrationTestComponent.Helper.injectEagerSingletons(component);
+		component.inject(this);
+
+		c0 = DaggerBriarIntegrationTestComponent.builder()
+				.testDatabaseConfigModule(new TestDatabaseConfigModule(t0Dir))
+				.build();
+		BriarIntegrationTestComponent.Helper.injectEagerSingletons(c0);
+
+		c1 = DaggerBriarIntegrationTestComponent.builder()
+				.testDatabaseConfigModule(new TestDatabaseConfigModule(t1Dir))
+				.build();
+		BriarIntegrationTestComponent.Helper.injectEagerSingletons(c1);
+
+		c2 = DaggerBriarIntegrationTestComponent.builder()
+				.testDatabaseConfigModule(new TestDatabaseConfigModule(t2Dir))
+				.build();
+		BriarIntegrationTestComponent.Helper.injectEagerSingletons(c2);
+	}
+
+	@Test
+	public void testCreateBackup() throws Exception {
+		// Create the backup
+		db0.transaction(false, txn -> {
+			assertNull(socialBackupManager0.getBackupMetadata(txn));
+			socialBackupManager0.createBackup(txn,
+					asList(contactId1From0, contactId2From0), 2);
+			BackupMetadata backupMetadata =
+					socialBackupManager0.getBackupMetadata(txn);
+			assertNotNull(backupMetadata);
+			List<Author> expected = asList(contact1From0.getAuthor(),
+					contact2From0.getAuthor());
+			assertEquals(expected, backupMetadata.getCustodians());
+			assertEquals(2, backupMetadata.getThreshold());
+			assertEquals(0, backupMetadata.getVersion());
+		});
+		// Sync the shard and backup messages to the contacts
+		sync0To1(2, true);
+		sync0To2(2, true);
+	}
+}