WIP make part of keyAgreement public, so it can be used for shard return

* 'social-backup-poc' of https://code.briarproject.org/briar/briar:
  Inject social backup eager singletons when Briar core is created.

briar-android/build.gradle

@@ -24,7 +24,7 @@ android {
 		targetSdkVersion 29
 		versionCode 10216
 		versionName "1.2.16"
-		applicationId "org.briarproject.briar.android"
+		applicationId "org.briarproject.briar.socialbackup"
 
 		vectorDrawables.useSupportLibrary = true
 		buildConfigField "String", "GitHash",

briar-android/proguard-rules.txt

@@ -40,3 +40,5 @@
 
 # Dependency injection annotations, needed for UI tests on older API levels
 -keep class javax.inject.**
+
+-keep class com.sun.jna.** { *; }

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

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-	<string name="app_name" translatable="false">Briar Debug</string>
+	<string name="app_name" translatable="false">Briar SB Debug</string>
-	<string name="app_package" translatable="false">org.briarproject.briar.android.debug</string>
+	<string name="app_package" translatable="false">org.briarproject.briar.socialbackup.debug</string>
 </resources>

briar-android/src/main/AndroidManifest.xml

@@ -153,14 +153,22 @@
 		</activity>
 
 		<activity
-			android:name="org.briarproject.briar.android.socialbackup.OldDistributedBackupActivity"
+			android:name="org.briarproject.briar.android.socialbackup.RecoverActivity"
-			android:label="@string/activity_name_old_distributed_backup"
+			android:label="@string/activity_name_recovery"
-			android:parentActivityName="org.briarproject.briar.android.settings.SettingsActivity">
+			android:parentActivityName="org.briarproject.briar.android.account.NewOrRecoverActivity">
 			<meta-data
 				android:name="android.support.PARENT_ACTIVITY"
-				android:value="org.briarproject.briar.android.settings.SettingsActivity" />
+				android:value="org.briarproject.briar.android.account.NewOrRecoverActivity" />
 		</activity>
 
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.CustodianHelpRecoverActivity"
+			android:label="@string/activity_name_custodian_help_recovery"
+			android:parentActivityName="org.briarproject.briar.android.conversation.ConversationActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.conversation.ConversationActivity" />
+		</activity>
 
 		<activity
 			android:name="org.briarproject.briar.android.conversation.ConversationActivity"

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

@@ -188,6 +188,7 @@ public interface AndroidComponent
 	Thread.UncaughtExceptionHandler exceptionHandler();
 
 	SocialBackupManager socialBackupManager();
+
     DatabaseComponent databaseComponent();
 
 	void inject(SignInReminderReceiver briarService);

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

@@ -48,6 +48,7 @@ import org.briarproject.briar.api.android.DozeWatchdog;
 import org.briarproject.briar.api.android.LockManager;
 import org.briarproject.briar.api.android.ScreenFilterMonitor;
 import org.briarproject.briar.api.test.TestAvatarCreator;
+import org.briarproject.briar.socialbackup.AndroidDarkCrystalModule;
 
 import java.io.File;
 import java.security.GeneralSecurityException;
@@ -82,6 +83,7 @@ import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 		SettingsModule.class,
 		DevReportModule.class,
 		ContactListModule.class,
+		AndroidDarkCrystalModule.class,
 		// below need to be within same scope as ViewModelProvider.Factory
 		ForumModule.class,
 		GroupListModule.class,

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

@@ -7,6 +7,7 @@ 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 org.briarproject.briar.android.socialbackup.RecoverActivity;
 
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TASK;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
@@ -14,7 +15,8 @@ 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 {
+		BaseFragment.BaseFragmentListener, SetupNewAccountChosenListener,
+		RecoverAccountListener {
 
 	@Override
 	public void injectActivity(ActivityComponent component) {
@@ -26,13 +28,13 @@ public class NewOrRecoverActivity extends BaseActivity implements
 		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);
+		setContentView(R.layout.activity_fragment_container);
 		NewOrRecoverFragment fragment = NewOrRecoverFragment.newInstance();
 		showInitialFragment(fragment);
 	}
 
 	@Override
-	public void setupNewAccountChosen () {
+	public void setupNewAccountChosen() {
 		finish();
 		Intent i = new Intent(this, SetupActivity.class);
 		i.addFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP |
@@ -41,7 +43,17 @@ public class NewOrRecoverActivity extends BaseActivity implements
 	}
 
 	@Override
-	public void runOnDbThread(Runnable runnable) {
+	public void recoverAccountChosen() {
+		finish();
+		Intent i = new Intent(this, RecoverActivity.class);
+		i.addFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP |
+				FLAG_ACTIVITY_CLEAR_TASK | FLAG_ACTIVITY_TASK_ON_HOME);
+		startActivity(i);
+	}
 
+	@Override
+	@Deprecated
+	public void runOnDbThread(Runnable runnable) {
+		throw new RuntimeException("Don't use this deprecated method here.");
 	}
 }

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

@@ -18,7 +18,8 @@ public class NewOrRecoverFragment extends BaseFragment {
 
 	public static final String TAG = NewOrRecoverFragment.class.getName();
 
-	protected SetupNewAccountChosenListener listener;
+	protected SetupNewAccountChosenListener setupNewAccountListener;
+	protected RecoverAccountListener recoverAccountListener;
 
 	public static NewOrRecoverFragment newInstance() {
 		Bundle bundle = new Bundle();
@@ -38,9 +39,14 @@ public class NewOrRecoverFragment extends BaseFragment {
 			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 newAccountButton = view.findViewById(R.id.buttonSetupNewAccount);
-		button.setOnClickListener(e -> {
+		newAccountButton.setOnClickListener(e -> {
-			listener.setupNewAccountChosen();
+			setupNewAccountListener.setupNewAccountChosen();
+		});
+
+		Button recoverAccountButton = view.findViewById(R.id.buttonRestoreAccount);
+		recoverAccountButton.setOnClickListener(e -> {
+			recoverAccountListener.recoverAccountChosen();
 		});
 		return view;
 	}
@@ -48,7 +54,8 @@ public class NewOrRecoverFragment extends BaseFragment {
 	@Override
 	public void onAttach(Context context) {
 		super.onAttach(context);
-		listener = (SetupNewAccountChosenListener) context;
+		setupNewAccountListener = (SetupNewAccountChosenListener) context;
+		recoverAccountListener = (RecoverAccountListener) context;
 	}
 
 	@Override

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

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

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

@@ -81,17 +81,18 @@ 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.CustodianHelpRecoverActivity;
 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.OwnerRecoveryModeExplainerFragment;
+import org.briarproject.briar.android.socialbackup.RecoverActivity;
+import org.briarproject.briar.android.socialbackup.ShardQrCodeFragment;
 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;
 
@@ -198,6 +199,8 @@ public interface ActivityComponent {
 
 	void inject(NewOrRecoverActivity newOrRecoverActivity);
 
+	void inject(CustodianHelpRecoverActivity custodianHelpRecoverActivity);
+
 	// Fragments
 
 	void inject(AuthorNameFragment fragment);
@@ -256,9 +259,11 @@ public interface ActivityComponent {
 
 	void inject(ThresholdSelectorFragment thresholdSelectorFragment);
 
+	void inject(ShardQrCodeFragment shardQrCodeFragment);
+
 	void inject(DistributedBackupActivity distributedBackupActivity);
-//    void inject(CreateBackupController createBackupController);
+
-//	void inject(CustodianDisplayFragment custodianDisplayFragment);
+	void inject(RecoverActivity recoverActivity);
 
 	void inject(DatabaseComponent databaseComponent);
 
@@ -266,9 +271,9 @@ public interface ActivityComponent {
 
 	void inject(ShardsSentFragment shardsSentFragment);
 
+	void inject(OwnerRecoveryModeExplainerFragment ownerRecoveryModeExplainerFragment);
+
 	void inject(ExistingBackupFragment existingBackupFragment);
 
 	void inject(NewOrRecoverFragment newOrRecoverFragment);
-
-	void inject(OldDistributedBackupActivity oldDistributedBackupActivity);
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationActivity.java

@@ -52,6 +52,7 @@ import org.briarproject.briar.android.conversation.ConversationVisitor.TextCache
 import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.introduction.IntroductionActivity;
 import org.briarproject.briar.android.privategroup.conversation.GroupActivity;
+import org.briarproject.briar.android.socialbackup.CustodianHelpRecoverActivity;
 import org.briarproject.briar.android.util.BriarSnackbarBuilder;
 import org.briarproject.briar.android.view.BriarRecyclerView;
 import org.briarproject.briar.android.view.ImagePreview;
@@ -396,6 +397,12 @@ public class ConversationActivity extends BriarActivity
 			case R.id.action_social_remove_person:
 				askToRemoveContact();
 				return true;
+			case R.id.action_help_recover_account:
+				if (contactId == null) return false;
+				Intent i = new Intent(this, CustodianHelpRecoverActivity.class);
+				i.putExtra(CONTACT_ID, contactId.getInt());
+				startActivity(i);
+				return true;
 			default:
 				return super.onOptionsItemSelected(item);
 		}

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationNoticeItem.java

@@ -3,6 +3,7 @@ package org.briarproject.briar.android.conversation;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.briar.api.conversation.ConversationRequest;
 import org.briarproject.briar.api.conversation.ConversationResponse;
+import org.briarproject.briar.api.socialbackup.ShardMessageHeader;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
@@ -30,6 +31,13 @@ class ConversationNoticeItem extends ConversationItem {
 		this.msgText = null;
 	}
 
+	ConversationNoticeItem(@LayoutRes int layoutRes, String text,
+			ShardMessageHeader r) {
+		super(layoutRes, r);
+		this.text = text;
+		this.msgText = null;
+	}
+
 	@Nullable
 	String getMsgText() {
 		return msgText;

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationVisitor.java

@@ -16,6 +16,7 @@ import org.briarproject.briar.api.introduction.IntroductionResponse;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationResponse;
+import org.briarproject.briar.api.socialbackup.ShardMessageHeader;
 
 import java.util.List;
 
@@ -292,6 +293,19 @@ class ConversationVisitor implements
 		}
 	}
 
+	@Override
+	public ConversationItem visitShardMessage(ShardMessageHeader r) {
+		if (r.isLocal()) {
+			String text = ctx.getString(R.string.social_backup_shard_sent);
+			return new ConversationNoticeItem(
+					R.layout.list_item_conversation_notice_out, text, r);
+		} else {
+			String text = ctx.getString(R.string.social_backup_shard_received);
+			return new ConversationNoticeItem(
+					R.layout.list_item_conversation_notice_in, text, r);
+		}
+	}
+
 	interface TextCache {
 		@Nullable
 		String getText(MessageId m);

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/CameraException.java

@@ -2,7 +2,7 @@ package org.briarproject.briar.android.keyagreement;
 
 import java.io.IOException;
 
-class CameraException extends IOException {
+public class CameraException extends IOException {
 
 	CameraException(String message) {
 		super(message);

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/QrCodeDecoder.java

@@ -30,7 +30,7 @@ import static java.util.logging.Level.WARNING;
 @SuppressWarnings("deprecation")
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
+public class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 
 	private static final Logger LOG =
 			Logger.getLogger(QrCodeDecoder.class.getName());
@@ -41,7 +41,7 @@ class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	private Camera camera = null;
 	private int cameraIndex = 0;
 
-	QrCodeDecoder(ResultCallback callback) {
+	public QrCodeDecoder(ResultCallback callback) {
 		this.callback = callback;
 	}
 
@@ -142,7 +142,7 @@ class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	}
 
 	@NotNullByDefault
-	interface ResultCallback {
+	public interface ResultCallback {
 
 		void handleResult(Result result);
 	}

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/QrCodeUtils.java

@@ -21,13 +21,13 @@ import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
-class QrCodeUtils {
+public class QrCodeUtils {
 
 	private static final Logger LOG =
 			Logger.getLogger(QrCodeUtils.class.getName());
 
 	@Nullable
-	static Bitmap createQrCode(DisplayMetrics dm, String input) {
+	public static Bitmap createQrCode(DisplayMetrics dm, String input) {
 		int smallestDimen = Math.min(dm.widthPixels, dm.heightPixels);
 		try {
 			// Generate QR code

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

@@ -0,0 +1,67 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Intent;
+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.fragment.BaseFragment;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+
+import javax.inject.Inject;
+
+import static org.briarproject.briar.android.conversation.ConversationActivity.CONTACT_ID;
+
+public class CustodianHelpRecoverActivity extends BriarActivity implements
+		BaseFragment.BaseFragmentListener, CustodianScanQrButtonListener {
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Inject
+	public SocialBackupManager socialBackupManager;
+
+	@Inject
+	public DatabaseComponent db;
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_recover); // TODO change this
+
+		Intent intent = getIntent();
+		int id = intent.getIntExtra(CONTACT_ID, -1);
+		if (id == -1) throw new IllegalStateException("No ContactId");
+		ContactId contactId = new ContactId(id);
+
+		// check if we have a shard for this secret owner
+		try {
+			db.transaction(false, txn -> {
+				if (!socialBackupManager.amCustodian(txn, contactId)) {
+					throw new DbException();
+				}
+				CustodianRecoveryModeExplainerFragment fragment =
+						new CustodianRecoveryModeExplainerFragment();
+				showInitialFragment(fragment);
+			});
+		} catch (DbException e) {
+			// TODO improve this
+			Toast.makeText(this,
+					"You do not hold a backup shard from this contact",
+					Toast.LENGTH_SHORT).show();
+			finish();
+		}
+	}
+
+	@Override
+	public void scanQrButtonClicked() {
+		// TODO scan qr code
+		finish();
+	}
+}

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

@@ -0,0 +1,51 @@
+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.android.fragment.BaseFragment;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import org.briarproject.briar.R;
+
+public class CustodianRecoveryModeExplainerFragment extends BaseFragment {
+
+	protected CustodianScanQrButtonListener listener;
+
+	public static final String TAG = CustodianRecoveryModeExplainerFragment.class.getName();
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_help_recover);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable
+			ViewGroup container, @Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_recovery_custodian_explainer,
+				container, false);
+
+		Button button = view.findViewById(R.id.button);
+		button.setOnClickListener(e -> listener.scanQrButtonClicked());
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (CustodianScanQrButtonListener) context;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+}
+

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

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

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

@@ -1,5 +1,6 @@
 package org.briarproject.briar.android.socialbackup;
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.briar.api.socialbackup.Shard;
 import org.briarproject.briar.api.socialbackup.DarkCrystal;
 import org.magmacollective.darkcrystal.secretsharingwrapper.SecretSharingWrapper;
@@ -10,10 +11,19 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.Random;
 
+import javax.inject.Inject;
+
+import dagger.Provides;
+
 import static org.briarproject.briar.socialbackup.SocialBackupConstants.SECRET_ID_BYTES;
 
+@NotNullByDefault
 public class DarkCrystalImpl implements DarkCrystal {
 
+    @Inject
+	DarkCrystalImpl() {
+	}
+
 	@Override
 	public List<Shard> createShards(SecretKey secret, int numShards,
 			int threshold) {

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

@@ -21,15 +21,16 @@ import javax.inject.Inject;
 
 public class DistributedBackupActivity extends BriarActivity implements
 		BaseFragment.BaseFragmentListener, ContactSelectorListener,
-		ThresholdDefinedListener, ShardsSentDismissedListener {
+		ThresholdDefinedListener,
+		ShardsSentFragment.ShardsSentDismissedListener {
 
 	private Collection<ContactId> custodians;
 
 	@Inject
-    public SocialBackupManager socialBackupManager;
+	public SocialBackupManager socialBackupManager;
 
 	@Inject
-    public DatabaseComponent db;
+	public DatabaseComponent db;
 
 	@Override
 	public void injectActivity(ActivityComponent component) {
@@ -40,22 +41,20 @@ public class DistributedBackupActivity extends BriarActivity implements
 	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);
+				BackupMetadata backupMetadata =
-				 if (backupMetadata == null) {
+						socialBackupManager.getBackupMetadata(txn);
-				CustodianSelectorFragment fragment =
+				if (backupMetadata == null) throw new DbException();
-						CustodianSelectorFragment.newInstance();
+				ExistingBackupFragment fragment =
-					 showInitialFragment(fragment);
+						ExistingBackupFragment.newInstance(backupMetadata);
-				 } else {
+				showInitialFragment(fragment);
-					 ExistingBackupFragment fragment = ExistingBackupFragment.newInstance(backupMetadata);
-					 showInitialFragment(fragment);
-				 }
 			});
 		} catch (DbException e) {
-			e.printStackTrace();
+			CustodianSelectorFragment fragment =
+					CustodianSelectorFragment.newInstance();
+			showInitialFragment(fragment);
 		}
 	}
 
@@ -65,17 +64,24 @@ public class DistributedBackupActivity extends BriarActivity implements
 				String.format("selected %d contacts", contacts.size()),
 				Toast.LENGTH_SHORT).show();
 		custodians = contacts;
-		ThresholdSelectorFragment fragment = ThresholdSelectorFragment.newInstance(contacts.size());
+		ThresholdSelectorFragment fragment =
+				ThresholdSelectorFragment.newInstance(contacts.size());
 		showNextFragment(fragment);
 	}
 
 	@Override
-	public void thresholdDefined(int threshold) throws DbException {
+	public void thresholdDefined(int threshold) {
-		db.transaction(false, txn -> {
+		try {
-			socialBackupManager.createBackup(txn, (List<ContactId>) custodians, threshold);
+			db.transaction(false, txn -> {
-			ShardsSentFragment fragment = new ShardsSentFragment();
+				socialBackupManager
-			showNextFragment(fragment);
+						.createBackup(txn, (List<ContactId>) custodians,
-		});
+								threshold);
+				ShardsSentFragment fragment = new ShardsSentFragment();
+				showNextFragment(fragment);
+			});
+		} catch (DbException e) {
+			e.printStackTrace();
+		}
 	}
 
 	@Override

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

@@ -2,9 +2,7 @@ package org.briarproject.briar.android.socialbackup;
 
 import androidx.annotation.UiThread;
 
-public interface ShardsSentDismissedListener {
+public interface ExplainerDismissedListener {
-
 	@UiThread
-	void shardsSentDismissed();
+	void explainerDismissed();
-
 }

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

@@ -1,39 +0,0 @@
-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/OwnerRecoveryModeExplainerFragment.java

@@ -0,0 +1,58 @@
+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 OwnerRecoveryModeExplainerFragment extends BaseFragment {
+
+	protected ExplainerDismissedListener listener;
+	public static final String TAG =
+			OwnerRecoveryModeExplainerFragment.class.getName();
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_recovery_mode);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_recovery_owner_explainer,
+				container, false);
+		Button button = view.findViewById(R.id.beginButton);
+		button.setOnClickListener(e -> listener.explainerDismissed());
+
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (ExplainerDismissedListener) context;
+	}
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+}

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

@@ -0,0 +1,73 @@
+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 android.widget.TextView;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+public class OwnerRecoveryModeMainFragment extends BaseFragment {
+
+	protected ScanQrButtonListener listener;
+
+	public static final String NUM_RECOVERED = "num_recovered";
+
+	public static final String TAG =
+			OwnerRecoveryModeMainFragment.class.getName();
+
+	public static OwnerRecoveryModeMainFragment newInstance(int numRecovered) {
+		Bundle args = new Bundle();
+		args.putInt(NUM_RECOVERED, numRecovered);
+		OwnerRecoveryModeMainFragment fragment =
+				new OwnerRecoveryModeMainFragment();
+		fragment.setArguments(args);
+		return fragment;
+	}
+
+	private int numShards;
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_recovery_mode);
+
+		Bundle args = requireArguments();
+		numShards = args.getInt(NUM_RECOVERED);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_recovery_owner_main,
+				container, false);
+
+		TextView textViewCount = view.findViewById(R.id.textViewShardCount);
+		textViewCount.setText(String.format("%d", numShards));
+
+		Button button = view.findViewById(R.id.button);
+		button.setOnClickListener(e -> listener.scanQrButtonClicked());
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (ScanQrButtonListener) context;
+	}
+
+}

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

@@ -0,0 +1,179 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.keyagreement.KeyAgreementResult;
+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 javax.annotation.Nullable;
+
+import androidx.annotation.UiThread;
+import androidx.core.app.ActivityCompat;
+
+import static android.Manifest.permission.CAMERA;
+import static android.content.pm.PackageManager.PERMISSION_GRANTED;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_PERMISSION_CAMERA_LOCATION;
+
+public class RecoverActivity extends BaseActivity implements
+		BaseFragment.BaseFragmentListener, ExplainerDismissedListener,
+		ScanQrButtonListener, ShardQrCodeFragment.ShardQrCodeEventListener {
+
+	@Override
+	public void keyAgreementFailed() {
+
+	}
+
+	@Nullable
+	@Override
+	public String keyAgreementWaiting() {
+		return null;
+	}
+
+	@Nullable
+	@Override
+	public String keyAgreementStarted() {
+		return null;
+	}
+
+	@Override
+	public void keyAgreementAborted(boolean remoteAborted) {
+
+	}
+
+	@Nullable
+	@Override
+	public String keyAgreementFinished(KeyAgreementResult result) {
+		return null;
+	}
+
+	private enum Permission {
+		UNKNOWN, GRANTED, SHOW_RATIONALE, PERMANENTLY_DENIED
+	}
+
+	private Permission cameraPermission = Permission.UNKNOWN;
+
+
+	private int numRecovered;
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_recover);
+
+		numRecovered = 0; // TODO - retrieve this from somewhere
+
+		// only show the explainer if we have no shards
+		if (numRecovered == 0) {
+			OwnerRecoveryModeExplainerFragment fragment =
+					new OwnerRecoveryModeExplainerFragment();
+			showInitialFragment(fragment);
+		} else {
+			OwnerRecoveryModeMainFragment fragment =
+					OwnerRecoveryModeMainFragment.newInstance(numRecovered);
+			showInitialFragment(fragment);
+		}
+	}
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void explainerDismissed() {
+		OwnerRecoveryModeMainFragment fragment =
+				OwnerRecoveryModeMainFragment.newInstance(numRecovered);
+		showNextFragment(fragment);
+	}
+
+	@Override
+	public void scanQrButtonClicked() {
+		if (checkPermissions()) showQrCodeFragment();
+	}
+
+
+	private void showQrCodeFragment() {
+		ShardQrCodeFragment f = ShardQrCodeFragment.newInstance();
+		showNextFragment(f);
+	}
+
+	private void requestPermissions() {
+		String[] permissions = new String[] {CAMERA};
+		ActivityCompat.requestPermissions(this, permissions,
+				REQUEST_PERMISSION_CAMERA_LOCATION);
+	}
+
+	@Override
+	@UiThread
+	public void onRequestPermissionsResult(int requestCode,
+			String[] permissions, int[] grantResults) {
+		if (requestCode != REQUEST_PERMISSION_CAMERA_LOCATION)
+			throw new AssertionError();
+		if (gotPermission(CAMERA, permissions, grantResults)) {
+			cameraPermission = Permission.GRANTED;
+		} else if (shouldShowRationale(CAMERA)) {
+			cameraPermission = Permission.SHOW_RATIONALE;
+		} else {
+			cameraPermission = Permission.PERMANENTLY_DENIED;
+		}
+		// If a permission dialog has been shown, showing the QR code fragment
+		// on this call path would cause a crash due to
+		// https://code.google.com/p/android/issues/detail?id=190966.
+		// In that case the isResumed flag prevents the fragment from being
+		// shown here, and showQrCodeFragmentIfAllowed() will be called again
+		// from onPostResume().
+		if (checkPermissions()) showQrCodeFragment();
+	}
+
+	private boolean gotPermission(String permission, String[] permissions,
+			int[] grantResults) {
+		for (int i = 0; i < permissions.length; i++) {
+			if (permission.equals(permissions[i]))
+				return grantResults[i] == PERMISSION_GRANTED;
+		}
+		return false;
+	}
+
+	private boolean shouldShowRationale(String permission) {
+		return ActivityCompat.shouldShowRequestPermissionRationale(this,
+				permission);
+	}
+
+	private boolean checkPermissions() {
+		if (areEssentialPermissionsGranted()) return true;
+		// If an essential permission has been permanently denied, ask the
+		// user to change the setting
+		if (cameraPermission == Permission.PERMANENTLY_DENIED) {
+			Toast.makeText(this,
+					"camera permission is denied",
+					Toast.LENGTH_SHORT).show();
+//			showDenialDialog(R.string.permission_camera_title,
+//					R.string.permission_camera_denied_body);
+			return false;
+		}
+		if (cameraPermission == Permission.SHOW_RATIONALE) {
+//			showRationale(R.string.permission_camera_title,
+//					R.string.permission_camera_request_body);
+			Toast.makeText(this,
+					"camera permission - show rationale",
+					Toast.LENGTH_SHORT).show();
+		} else {
+			requestPermissions();
+		}
+		return false;
+	}
+
+	@Override
+	@Deprecated
+	public void runOnDbThread(Runnable runnable) {
+		throw new RuntimeException("Don't use this deprecated method here.");
+	}
+
+	private boolean areEssentialPermissionsGranted() {
+		return cameraPermission == Permission.GRANTED;
+	}
+}

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

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

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

@@ -0,0 +1,381 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.os.Bundle;
+import android.util.DisplayMetrics;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.LinearLayout;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import com.google.zxing.Result;
+
+import org.briarproject.bramble.api.UnsupportedVersionException;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.keyagreement.KeyAgreementResult;
+import org.briarproject.bramble.api.keyagreement.KeyAgreementTask;
+import org.briarproject.bramble.api.keyagreement.Payload;
+import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
+import org.briarproject.bramble.api.keyagreement.PayloadParser;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementAbortedEvent;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementFailedEvent;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementFinishedEvent;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementListeningEvent;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementStartedEvent;
+import org.briarproject.bramble.api.keyagreement.event.KeyAgreementWaitingEvent;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.fragment.BaseEventFragment;
+import org.briarproject.briar.android.keyagreement.CameraException;
+import org.briarproject.briar.android.keyagreement.CameraView;
+import org.briarproject.briar.android.keyagreement.ContactExchangeErrorFragment;
+import org.briarproject.briar.android.keyagreement.QrCodeDecoder;
+import org.briarproject.briar.android.keyagreement.QrCodeUtils;
+import org.briarproject.briar.android.view.QrCodeView;
+
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+import javax.inject.Provider;
+
+import androidx.annotation.UiThread;
+
+import static android.content.pm.ActivityInfo.SCREEN_ORIENTATION_NOSENSOR;
+import static android.view.View.INVISIBLE;
+import static android.view.View.VISIBLE;
+import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
+import static android.widget.LinearLayout.HORIZONTAL;
+import static android.widget.Toast.LENGTH_LONG;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class ShardQrCodeFragment extends BaseEventFragment
+		implements QrCodeDecoder.ResultCallback, QrCodeView.FullscreenListener {
+
+	static final String TAG = org.briarproject.briar.android.keyagreement.KeyAgreementFragment.class.getName();
+
+	private static final Logger LOG = Logger.getLogger(TAG);
+	@SuppressWarnings("CharsetObjectCanBeUsed") // Requires minSdkVersion >= 19
+	private static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
+
+	@Inject
+	Provider<KeyAgreementTask> keyAgreementTaskProvider;
+	@Inject
+	PayloadEncoder payloadEncoder;
+	@Inject
+	PayloadParser payloadParser;
+	@Inject
+	@IoExecutor
+	Executor ioExecutor;
+	@Inject
+	EventBus eventBus;
+
+	private CameraView cameraView;
+	private LinearLayout cameraOverlay;
+	private View statusView;
+	private QrCodeView qrCodeView;
+	private TextView status;
+
+	private boolean gotRemotePayload;
+	private volatile boolean gotLocalPayload;
+	private KeyAgreementTask task;
+	private ShardQrCodeEventListener
+			listener;
+
+	public static ShardQrCodeFragment newInstance() {
+		Bundle args = new Bundle();
+		ShardQrCodeFragment
+				fragment = new ShardQrCodeFragment();
+		fragment.setArguments(args);
+		return fragment;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		listener = (ShardQrCodeEventListener) context;
+	}
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		return inflater.inflate(R.layout.fragment_keyagreement_qr, container,
+				false);
+	}
+
+	@Override
+	public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(view, savedInstanceState);
+		cameraView = view.findViewById(R.id.camera_view);
+		cameraOverlay = view.findViewById(R.id.camera_overlay);
+		statusView = view.findViewById(R.id.status_container);
+		status = view.findViewById(R.id.connect_status);
+		qrCodeView = view.findViewById(R.id.qr_code_view);
+		qrCodeView.setFullscreenListener(this);
+	}
+
+	@Override
+	public void onActivityCreated(@Nullable Bundle savedInstanceState) {
+		super.onActivityCreated(savedInstanceState);
+		requireActivity().setRequestedOrientation(SCREEN_ORIENTATION_NOSENSOR);
+		cameraView.setPreviewConsumer(new QrCodeDecoder(this));
+	}
+
+	@Override
+	public void onStart() {
+		super.onStart();
+		try {
+			cameraView.start();
+		} catch (CameraException e) {
+			logCameraExceptionAndFinish(e);
+		}
+		startListening();
+	}
+
+	@Override
+	public void setFullscreen(boolean fullscreen) {
+		LinearLayout.LayoutParams statusParams, qrCodeParams;
+		if (fullscreen) {
+			// Grow the QR code view to fill its parent
+			statusParams = new LinearLayout.LayoutParams(0, 0, 0f);
+			qrCodeParams = new LinearLayout.LayoutParams(MATCH_PARENT, MATCH_PARENT, 1f);
+		} else {
+			// Shrink the QR code view to fill half its parent
+			if (cameraOverlay.getOrientation() == HORIZONTAL) {
+				statusParams = new LinearLayout.LayoutParams(0, MATCH_PARENT, 1f);
+				qrCodeParams = new LinearLayout.LayoutParams(0, MATCH_PARENT, 1f);
+			} else {
+				statusParams = new LinearLayout.LayoutParams(MATCH_PARENT, 0, 1f);
+				qrCodeParams = new LinearLayout.LayoutParams(MATCH_PARENT, 0, 1f);
+			}
+		}
+		statusView.setLayoutParams(statusParams);
+		qrCodeView.setLayoutParams(qrCodeParams);
+		cameraOverlay.invalidate();
+	}
+
+	@Override
+	public void onStop() {
+		super.onStop();
+		stopListening();
+		try {
+			cameraView.stop();
+		} catch (CameraException e) {
+			logCameraExceptionAndFinish(e);
+		}
+	}
+
+	@UiThread
+	private void logCameraExceptionAndFinish(CameraException e) {
+		logException(LOG, WARNING, e);
+		Toast.makeText(getActivity(), R.string.camera_error,
+				LENGTH_LONG).show();
+		finish();
+	}
+
+	@UiThread
+	private void startListening() {
+		KeyAgreementTask oldTask = task;
+		KeyAgreementTask newTask = keyAgreementTaskProvider.get();
+		task = newTask;
+		ioExecutor.execute(() -> {
+			if (oldTask != null) oldTask.stopListening();
+			newTask.listen();
+		});
+	}
+
+	@UiThread
+	private void stopListening() {
+		KeyAgreementTask oldTask = task;
+		ioExecutor.execute(() -> {
+			if (oldTask != null) oldTask.stopListening();
+		});
+	}
+
+	@UiThread
+	private void reset() {
+		// If we've stopped the camera view, restart it
+		if (gotRemotePayload) {
+			try {
+				cameraView.start();
+			} catch (CameraException e) {
+				logCameraExceptionAndFinish(e);
+				return;
+			}
+		}
+		statusView.setVisibility(INVISIBLE);
+		cameraView.setVisibility(VISIBLE);
+		gotRemotePayload = false;
+		gotLocalPayload = false;
+		startListening();
+	}
+
+	@UiThread
+	private void qrCodeScanned(String content) {
+		try {
+			byte[] payloadBytes = content.getBytes(ISO_8859_1);
+			if (LOG.isLoggable(INFO))
+				LOG.info("Remote payload is " + payloadBytes.length + " bytes");
+			Payload remotePayload = payloadParser.parse(payloadBytes);
+			gotRemotePayload = true;
+			cameraView.stop();
+			cameraView.setVisibility(INVISIBLE);
+			statusView.setVisibility(VISIBLE);
+			status.setText(R.string.connecting_to_device);
+			task.connectAndRunProtocol(remotePayload);
+		} catch (UnsupportedVersionException e) {
+			reset();
+			String msg;
+			if (e.isTooOld()) {
+				msg = getString(R.string.qr_code_too_old,
+						getString(R.string.app_name));
+			} else {
+				msg = getString(R.string.qr_code_too_new,
+						getString(R.string.app_name));
+			}
+			showNextFragment(ContactExchangeErrorFragment.newInstance(msg));
+		} catch (CameraException e) {
+			logCameraExceptionAndFinish(e);
+		} catch (IOException | IllegalArgumentException e) {
+			LOG.log(WARNING, "QR Code Invalid", e);
+			reset();
+			Toast.makeText(getActivity(), R.string.qr_code_invalid,
+					LENGTH_LONG).show();
+		}
+	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof KeyAgreementListeningEvent) {
+			KeyAgreementListeningEvent event = (KeyAgreementListeningEvent) e;
+			gotLocalPayload = true;
+			setQrCode(event.getLocalPayload());
+		} else if (e instanceof KeyAgreementFailedEvent) {
+			keyAgreementFailed();
+		} else if (e instanceof KeyAgreementWaitingEvent) {
+			keyAgreementWaiting();
+		} else if (e instanceof KeyAgreementStartedEvent) {
+			keyAgreementStarted();
+		} else if (e instanceof KeyAgreementAbortedEvent) {
+			KeyAgreementAbortedEvent event = (KeyAgreementAbortedEvent) e;
+			keyAgreementAborted(event.didRemoteAbort());
+		} else if (e instanceof KeyAgreementFinishedEvent) {
+			keyAgreementFinished(((KeyAgreementFinishedEvent) e).getResult());
+		}
+	}
+
+	@UiThread
+	private void keyAgreementFailed() {
+		reset();
+		listener.keyAgreementFailed();
+	}
+
+	@UiThread
+	private void keyAgreementWaiting() {
+		status.setText(listener.keyAgreementWaiting());
+	}
+
+	@UiThread
+	private void keyAgreementStarted() {
+		qrCodeView.setVisibility(INVISIBLE);
+		statusView.setVisibility(VISIBLE);
+		status.setText(listener.keyAgreementStarted());
+	}
+
+	@UiThread
+	private void keyAgreementAborted(boolean remoteAborted) {
+		reset();
+		listener.keyAgreementAborted(remoteAborted);
+	}
+
+	@UiThread
+	private void keyAgreementFinished(KeyAgreementResult result) {
+		statusView.setVisibility(VISIBLE);
+		status.setText(listener.keyAgreementFinished(result));
+	}
+
+	private void setQrCode(Payload localPayload) {
+		Context context = getContext();
+		if (context == null) return;
+		DisplayMetrics dm = context.getResources().getDisplayMetrics();
+		ioExecutor.execute(() -> {
+			byte[] payloadBytes = payloadEncoder.encode(localPayload);
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Local payload is " + payloadBytes.length
+						+ " bytes");
+			}
+			// Use ISO 8859-1 to encode bytes directly as a string
+			String content = new String(payloadBytes, ISO_8859_1);
+			Bitmap qrCode = QrCodeUtils.createQrCode(dm, content);
+			runOnUiThreadUnlessDestroyed(() -> qrCodeView.setQrCode(qrCode));
+		});
+	}
+
+	@Override
+	public void handleResult(Result result) {
+		runOnUiThreadUnlessDestroyed(() -> {
+			LOG.info("Got result from decoder");
+			// Ignore results until the KeyAgreementTask is ready
+			if (!gotLocalPayload) return;
+			if (!gotRemotePayload) qrCodeScanned(result.getText());
+		});
+	}
+
+	@Override
+	protected void finish() {
+		getActivity().getSupportFragmentManager().popBackStack();
+	}
+
+	@NotNullByDefault
+	interface ShardQrCodeEventListener {
+
+		@UiThread
+		void keyAgreementFailed();
+
+		// Should return a string to be displayed as status.
+		@UiThread
+		@Nullable
+		String keyAgreementWaiting();
+
+		// Should return a string to be displayed as status.
+		@UiThread
+		@Nullable
+		String keyAgreementStarted();
+
+		// Will show an error fragment.
+		@UiThread
+		void keyAgreementAborted(boolean remoteAborted);
+
+		// Should return a string to be displayed as status.
+		@UiThread
+		@Nullable
+		String keyAgreementFinished(KeyAgreementResult result);
+	}
+}

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

@@ -13,48 +13,58 @@ import org.briarproject.briar.android.fragment.BaseFragment;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
 
 public class ShardsSentFragment extends BaseFragment {
 
-    public static final String TAG = ShardsSentFragment.class.getName();
+	public static final String TAG = ShardsSentFragment.class.getName();
 
-    protected ShardsSentDismissedListener listener;
+	interface ShardsSentDismissedListener {
 
-    @Override
+		@UiThread
-    public void onCreate(@Nullable Bundle savedInstanceState) {
+		void shardsSentDismissed();
-        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);
+	protected ShardsSentDismissedListener listener;
-        button.setOnClickListener(e -> {
-            listener.shardsSentDismissed();
-        });
 
-        return view;
+	@Override
-    }
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_distributed_backup);
+	}
 
-    @Override
+	@Nullable
-    public void onAttach(Context context) {
+	@Override
-        super.onAttach(context);
+	public View onCreateView(@NonNull LayoutInflater inflater,
-        listener = (ShardsSentDismissedListener) context;
+			@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
+	@Override
-    public String getUniqueTag() {
+	public String getUniqueTag() {
-        return TAG;
+		return TAG;
-    }
+	}
 
-    @Override
+	@Override
-    public void injectFragment(ActivityComponent component) {
+	public void injectFragment(ActivityComponent component) {
-        component.inject(this);
+		component.inject(this);
-    }
+	}
 
 }

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

@@ -8,162 +8,175 @@ 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;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 
 public class ThresholdSelectorFragment extends BaseFragment {
 
-    public static final String TAG = ThresholdSelectorFragment.class.getName();
+	public static final String TAG = ThresholdSelectorFragment.class.getName();
-    private static final String NUMBER_CUSTODIANS = "numberCustodians";
+	private static final String NUMBER_CUSTODIANS = "numberCustodians";
 
-    protected ThresholdDefinedListener listener;
+	protected ThresholdDefinedListener listener;
 
-    // TODO this should be the actual number of custodians
+	private int numberOfCustodians;
-    private int numberOfCustodians;
+	private int threshold;
-    private int threshold;
+	private int recommendedThreshold;
-    private int recommendedThreshold;
+	private SeekBar seekBar;
-    private SeekBar seekBar;
+	private TextView thresholdRepresentation;
-    private TextView thresholdRepresentation;
+	private TextView message;
-    private TextView message;
+	private TextView mOfn;
-    private TextView mOfn;
 
-    public static ThresholdSelectorFragment newInstance(int numberCustodians) {
+	public static ThresholdSelectorFragment newInstance(int numberCustodians) {
-        Bundle bundle = new Bundle();
+		Bundle bundle = new Bundle();
-        bundle.putInt(NUMBER_CUSTODIANS, numberCustodians);
+		bundle.putInt(NUMBER_CUSTODIANS, numberCustodians);
-        ThresholdSelectorFragment fragment = new ThresholdSelectorFragment();
+		ThresholdSelectorFragment fragment = new ThresholdSelectorFragment();
-        fragment.setArguments(bundle);
+		fragment.setArguments(bundle);
-        return fragment;
+		return fragment;
-    }
+	}
 
-    @Override
+	@Override
-    public void onCreate(@Nullable Bundle savedInstanceState) {
+	public void onCreate(@Nullable Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
+		super.onCreate(savedInstanceState);
-        requireActivity().setTitle(R.string.title_define_threshold);
+		requireActivity().setTitle(R.string.title_define_threshold);
-    }
+	}
 
-    @Nullable
+	@Nullable
-    @Override
+	@Override
-    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
+	public View onCreateView(@NonNull LayoutInflater inflater,
-        View view = inflater.inflate(R.layout.fragment_select_threshold,
+			@Nullable ViewGroup container,
-                container, false);
+			@Nullable Bundle savedInstanceState) {
-	    Bundle args = requireArguments();
+		View view = inflater.inflate(R.layout.fragment_select_threshold,
-	    numberOfCustodians = args.getInt(NUMBER_CUSTODIANS);
+				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);
 
-        seekBar = view.findViewById(R.id.seekBar);
+		if (numberOfCustodians == 2) {
-        thresholdRepresentation = view.findViewById(R.id.textViewThresholdRepresentation);
+			message.setText(R.string.threshold_too_few_custodians);
-        message = view.findViewById(R.id.textViewMessage);
+		}
-        mOfn = view.findViewById(R.id.textViewmOfn);
+		if (numberOfCustodians > 3) {
-        int max = numberOfCustodians - 3;
+			seekBar.setMax(numberOfCustodians -3);
-        seekBar.setMax(max);
+			seekBar.setProgress(threshold - 2);
-        seekBar.setOnSeekBarChangeListener(new SeekBarListener());
+			seekBar.setOnSeekBarChangeListener(new SeekBarListener());
-        recommendedThreshold = SecretSharingWrapper.defaultThreshold(numberOfCustodians);
+			recommendedThreshold =
-        threshold = recommendedThreshold;
+					SecretSharingWrapper.defaultThreshold(numberOfCustodians);
-        seekBar.setProgress(threshold - 2);
+			threshold = recommendedThreshold;
 
-        thresholdRepresentation.setText(buildThresholdRepresentationString());
+		} else {
-        setmOfnText();
+			seekBar.setEnabled(false);
-        return view;
+			threshold = 2;
+			seekBar.setMax(numberOfCustodians);
+			seekBar.setProgress(threshold);
+			TextView t = view.findViewById(R.id.title_threshold);
+			t.setText(R.string.threshold_disabled);
+		}
+		thresholdRepresentation.setText(buildThresholdRepresentationString());
+		setmOfnText();
+		return view;
 //        return super.onCreateView(inflater, container, savedInstanceState);
-    }
+	}
 
-    private void setmOfnText() {
+	private void setmOfnText() {
-        mOfn.setText(String.format("%d of %d contacts needed to recover your account", threshold, numberOfCustodians));
+		mOfn.setText(String.format(
-    }
+				getString(R.string.threshold_m_of_n), threshold,
+				numberOfCustodians));
+	}
 
-    @Override
+	@Override
-    public void onAttach(Context context) {
+	public void onAttach(Context context) {
-        super.onAttach(context);
+		super.onAttach(context);
-        listener = (ThresholdDefinedListener) context;
+		listener = (ThresholdDefinedListener) context;
-    }
+	}
 
 
-    @Override
+	@Override
-    public String getUniqueTag() {
+	public String getUniqueTag() {
-        return TAG;
+		return TAG;
-    }
+	}
 
-    @Override
+	@Override
-    public void injectFragment(ActivityComponent component) {
+	public void injectFragment(ActivityComponent component) {
-        component.inject(this);
+		component.inject(this);
-    }
+	}
 
-    @Override
+	@Override
-    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+	public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
-        inflater.inflate(R.menu.define_threshold_actions, menu);
+		inflater.inflate(R.menu.define_threshold_actions, menu);
-        super.onCreateOptionsMenu(menu, inflater);
+		super.onCreateOptionsMenu(menu, inflater);
-    }
+	}
 
-    @Override
+	@Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+	public boolean onOptionsItemSelected(MenuItem item) {
-        switch (item.getItemId()) {
+		switch (item.getItemId()) {
-            case R.id.action_threshold_defined:
+			case R.id.action_threshold_defined:
-                try {
+				try {
-                    listener.thresholdDefined(threshold);
+					listener.thresholdDefined(threshold);
-                } catch (DbException e) {
+				} catch (DbException e) {
-                    e.printStackTrace();
+					e.printStackTrace();
-                }
+				}
-                return true;
+				return true;
-            default:
+			default:
-                return super.onOptionsItemSelected(item);
+				return super.onOptionsItemSelected(item);
-        }
+		}
-    }
+	}
 
-    private String buildThresholdRepresentationString () {
+	private String buildThresholdRepresentationString() {
-        String thresholdRepresentationText = "";
+		String thresholdRepresentationText = "";
-        for (int i = 0; i < threshold; i++) {
+		for (int i = 0; i < threshold; i++) {
-            thresholdRepresentationText += getString(R.string.filled_bullet);
+			thresholdRepresentationText += getString(R.string.filled_bullet);
-        }
+		}
-        for (int i = 0; i < (numberOfCustodians - threshold); i++) {
+		for (int i = 0; i < (numberOfCustodians - threshold); i++) {
-            thresholdRepresentationText += getString(R.string.linear_bullet);
+			thresholdRepresentationText += getString(R.string.linear_bullet);
-        }
+		}
-        return thresholdRepresentationText;
+		return thresholdRepresentationText;
-    }
+	}
 
-    private class SeekBarListener implements SeekBar.OnSeekBarChangeListener {
+	private class SeekBarListener implements SeekBar.OnSeekBarChangeListener {
 
-        @Override
+		@Override
-        public void onProgressChanged(SeekBar seekBar, int progress,
+		public void onProgressChanged(SeekBar seekBar, int progress,
-                boolean fromUser) {
+				boolean fromUser) {
-	        threshold = progress + 2;
+			threshold = progress + 2;
 
-            thresholdRepresentation.setText(
+			thresholdRepresentation.setText(
-                    buildThresholdRepresentationString()
+					buildThresholdRepresentationString()
-            );
+			);
-            setmOfnText();
+			setmOfnText();
 
-            int sanityLevel = SecretSharingWrapper.thresholdSanity(threshold, numberOfCustodians);
+			int sanityLevel = SecretSharingWrapper
-            int text = R.string.threshold_secure;
+					.thresholdSanity(threshold, numberOfCustodians);
-            if (threshold == recommendedThreshold) text = R.string.threshold_recommended;
+			int text = R.string.threshold_secure;
-            if (sanityLevel < -1) text = R.string.threshold_low_insecure;
+			if (threshold == recommendedThreshold)
-            if (sanityLevel > 0) text = R.string.threshold_high_insecure;
+				text = R.string.threshold_recommended;
-            message.setText(text);
+			if (sanityLevel < -1) text = R.string.threshold_low_insecure;
-            // TODO change colour of thresholdRepresentation to green/red based on sanityLevel
+			if (sanityLevel > 0) text = R.string.threshold_high_insecure;
-        }
+			message.setText(text);
+			// TODO change colour of thresholdRepresentation to green/red based on sanityLevel
+		}
 
-        @Override
+		@Override
-        public void onStartTrackingTouch(SeekBar seekBar) {
+		public void onStartTrackingTouch(SeekBar seekBar) {
-            // do nothing
+			// do nothing
-        }
+		}
 
-        @Override
+		@Override
-        public void onStopTrackingTouch(SeekBar seekBar) {
+		public void onStopTrackingTouch(SeekBar seekBar) {
-            // do nothing
+			// do nothing
-        }
+		}
 
-    }
+	}
 
 }

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

@@ -0,0 +1,16 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.briar.android.socialbackup.DarkCrystalImpl;
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class AndroidDarkCrystalModule {
+
+	@Provides
+	DarkCrystal darkCrystal(DarkCrystalImpl darkCrystal) {
+		return darkCrystal;
+	}
+}

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

@@ -0,0 +1,8 @@
+<?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/fragment_recovery_owner_explainer.xml

@@ -34,7 +34,7 @@
 		app:srcCompat="@drawable/qr_code_intro" />
 
 	<Button
-		android:id="@+id/button"
+		android:id="@+id/beginButton"
 		android:layout_width="match_parent"
 		android:layout_height="wrap_content"
 		android:layout_marginTop="24dp"

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

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
 
-	<string name="app_name" translatable="false">Briar</string>
+	<string name="app_name" translatable="false">Briar SB</string>
-	<string name="app_package" translatable="false">org.briarproject.briar.android</string>
+	<string name="app_package" translatable="false">org.briarproject.briar.socialbackup</string>
 
 	<!-- Setup -->
 	<string name="setup_title">Welcome to Briar</string>
@@ -655,12 +655,15 @@
 	<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">Choose the minimum number of trusted contacts needed to restore your account</string>
+	<string name="threshold_disabled">Two trusted contacts will be 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_too_few_custodians">Danger of loss - more contacts recommended</string>
 	<string name="threshold_defined">Choose Threshold</string>
+	<string name="threshold_m_of_n">%d of %d contacts needed to recover your account</string>
 
 	<string name="backup_done_info">Backup pieces sent to trusted contacts</string>
 	<string name="backup_done_dismiss">Got it</string>
@@ -691,7 +694,7 @@
 
 	<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_define_threshold">Threshold</string>
 	<string name="title_recovery_mode">Recovery Mode</string>
 	<string name="title_help_recover">Help recover account</string>
 
@@ -706,11 +709,17 @@
 
 	<!-- Symbols for visualising threshold values for social backup -->
 	<string name="filled_bullet">\u25CF</string>
-    <string name="linear_bullet">\u25CB</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>
 
+	<!-- conversation -->
+	<string name="social_backup_shard_received">You have received a social backup shard.</string>
+	<string name="social_backup_shard_sent">You have sent a social backup shard.</string>
+
 	<string name="activity_name_new_or_recover_account">Create new account or recover existing account</string>
+	<string name="activity_name_recovery">Recover Account</string>
+	<string name="activity_name_custodian_help_recovery">Help recover account</string>
 </resources>

briar-api/src/main/java/org/briarproject/briar/api/conversation/ConversationMessageVisitor.java

@@ -10,6 +10,7 @@ import org.briarproject.briar.api.introduction.IntroductionResponse;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationResponse;
+import org.briarproject.briar.api.socialbackup.ShardMessageHeader;
 
 @NotNullByDefault
 public interface ConversationMessageVisitor<T> {
@@ -31,4 +32,6 @@ public interface ConversationMessageVisitor<T> {
 	T visitIntroductionRequest(IntroductionRequest r);
 
 	T visitIntroductionResponse(IntroductionResponse r);
+
+	T visitShardMessage(ShardMessageHeader r);
 }

briar-api/src/main/java/org/briarproject/briar/api/keyagreement/KeyAgreementUtils.java

@@ -0,0 +1,35 @@
+package org.briarproject.briar.api.keyagreement;
+
+public class KeyAgreementUtils {
+
+	public enum BluetoothDecision {
+		/**
+		 * We haven't asked the user about Bluetooth discoverability.
+		 */
+		UNKNOWN,
+
+		/**
+		 * The device doesn't have a Bluetooth adapter.
+		 */
+		NO_ADAPTER,
+
+		/**
+		 * We're waiting for the user to accept or refuse discoverability.
+		 */
+		WAITING,
+
+		/**
+		 * The user has accepted discoverability.
+		 */
+		ACCEPTED,
+
+		/**
+		 * The user has refused discoverability.
+		 */
+		REFUSED
+	}
+
+	public enum Permission {
+		UNKNOWN, GRANTED, SHOW_RATIONALE, PERMANENTLY_DENIED
+	}
+}

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

@@ -0,0 +1,36 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.attachment.AttachmentHeader;
+import org.briarproject.briar.api.conversation.ConversationMessageHeader;
+import org.briarproject.briar.api.conversation.ConversationMessageVisitor;
+
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ShardMessageHeader extends ConversationMessageHeader {
+
+	private final List<AttachmentHeader> attachmentHeaders;
+
+	public ShardMessageHeader(MessageId id, GroupId groupId, long timestamp,
+			boolean local, boolean read, boolean sent, boolean seen,
+			List<AttachmentHeader> headers) {
+		super(id, groupId, timestamp, local, read, sent, seen);
+		this.attachmentHeaders = headers;
+	}
+
+	public List<AttachmentHeader> getAttachmentHeaders() {
+		return attachmentHeaders;
+	}
+
+	@Override
+	public <T> T accept(ConversationMessageVisitor<T> v) {
+		return v.visitShardMessage(this);
+	}
+
+}

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

@@ -0,0 +1,19 @@
+package org.briarproject.briar.api.socialbackup;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.conversation.event.ConversationMessageReceivedEvent;
+
+import jdk.nashorn.internal.ir.annotations.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ShardReceivedEvent
+		extends ConversationMessageReceivedEvent<ShardMessageHeader> {
+
+	public ShardReceivedEvent(ShardMessageHeader shardMessageHeader,
+			ContactId contactId) {
+		super(shardMessageHeader, contactId);
+	}
+
+}

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

@@ -1,17 +1,22 @@
 package org.briarproject.briar.api.socialbackup;
 
+import org.briarproject.bramble.api.contact.Contact;
 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 org.briarproject.briar.api.conversation.ConversationManager;
+import org.briarproject.briar.api.conversation.ConversationMessageHeader;
 
+import java.util.Collection;
 import java.util.List;
 
 import javax.annotation.Nullable;
 
 @NotNullByDefault
-public interface SocialBackupManager {
+public interface SocialBackupManager extends
+		ConversationManager.ConversationClient {
 
 	/**
 	 * The unique ID of the social backup client.
@@ -44,4 +49,10 @@ public interface SocialBackupManager {
 	 */
 	void createBackup(Transaction txn, List<ContactId> custodianIds,
 			int threshold) throws DbException;
+
+	@Override
+	Collection<ConversationMessageHeader> getMessageHeaders(
+			Transaction txn, ContactId contactId) throws DbException;
+
+	boolean amCustodian(Transaction txn, ContactId contactId);
 }

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

@@ -11,6 +11,7 @@ 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.socialbackup.DefaultSocialBackupModule;
 
 public interface BriarCoreEagerSingletons {
 

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

@@ -0,0 +1,15 @@
+package org.briarproject.briar.socialbackup;
+
+import org.briarproject.briar.api.socialbackup.DarkCrystal;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class DefaultDarkCrystalModule {
+
+	@Provides
+	DarkCrystal darkCrystal(DarkCrystalStub darkCrystal) {
+		return darkCrystal;
+	}
+}

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

@@ -10,6 +10,7 @@ public interface SocialBackupConstants {
 	String GROUP_KEY_VERSION = "version";
 
 	// Message metadata keys
+	String MSG_KEY_TIMESTAMP = "timestamp";
 	String MSG_KEY_MESSAGE_TYPE = "messageType";
 	String MSG_KEY_LOCAL = "local";
 	String MSG_KEY_VERSION = "version";

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

@@ -2,7 +2,6 @@ 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;
@@ -34,14 +33,23 @@ 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.sync.MessageStatus;
 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.attachment.AttachmentHeader;
+import org.briarproject.briar.api.client.MessageTracker;
+import org.briarproject.briar.api.conversation.ConversationManager;
+import org.briarproject.briar.api.conversation.ConversationMessageHeader;
+import org.briarproject.briar.api.conversation.DeletionResult;
 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.ShardMessageHeader;
+import org.briarproject.briar.api.socialbackup.ShardReceivedEvent;
 import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+import org.briarproject.briar.client.ConversationClientImpl;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -49,22 +57,25 @@ import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 
 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.client.MessageTrackerConstants.MSG_KEY_READ;
 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_TIMESTAMP;
 import static org.briarproject.briar.socialbackup.SocialBackupConstants.MSG_KEY_VERSION;
 
 @NotNullByDefault
-class SocialBackupManagerImpl extends BdfIncomingMessageHook
+class SocialBackupManagerImpl extends ConversationClientImpl
 		implements SocialBackupManager, OpenDatabaseHook, ContactHook,
 		ClientVersioningHook {
 
@@ -100,8 +111,11 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 			ContactManager contactManager,
 			CryptoComponent crypto,
 			DarkCrystal darkCrystal,
-			Clock clock) {
+			Clock clock,
-		super(db, clientHelper, metadataParser);
+			MessageTracker messageTracker,
+			ConversationManager conversationManager
+	) {
+		super(db, clientHelper, metadataParser, messageTracker);
 		this.clientVersioningManager = clientVersioningManager;
 		this.transportPropertyManager = transportPropertyManager;
 		this.contactGroupFactory = contactGroupFactory;
@@ -165,20 +179,21 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 	protected boolean incomingMessage(Transaction txn, Message m, BdfList body,
 			BdfDictionary meta) throws DbException, FormatException {
 		MessageType type = MessageType.fromValue(body.getLong(0).intValue());
+		System.out.println("GOT INCOMING DC MESSAGE");
 		if (type == SHARD) {
 			// Only one shard should be received from each contact
 			if (findMessage(txn, m.getGroupId(), SHARD, false) != null) {
 				throw new FormatException();
 			}
+			ContactId contactId = getContactId(txn, m.getGroupId());
 			// 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)) {
+					if (cd.getContact().getId().equals(contactId)) {
 						it.set(new ContactData(cd.getContact(),
 								cd.getProperties(), shard));
 						updateBackup(txn, contactData);
@@ -186,6 +201,12 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 					}
 				}
 			}
+			messageTracker.trackIncomingMessage(txn, m);
+
+			MessageStatus status = db.getMessageStatus(txn, contactId,
+					m.getId());
+			txn.attach(new ShardReceivedEvent(
+					createShardMessageHeader(m, meta, status), contactId));
 		} else if (type == BACKUP) {
 			// Keep the newest version of the backup, delete any older versions
 			int version = meta.getLong(MSG_KEY_VERSION).intValue();
@@ -209,6 +230,17 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 		return false;
 	}
 
+	public boolean amCustodian(Transaction txn, ContactId contactId) {
+		try {
+			GroupId groupId = getContactGroup(db.getContact(txn, contactId)).getId();
+			return findMessage(txn, groupId, SHARD, false) != null;
+		} catch (DbException e) {
+			return false;
+		} catch (FormatException e) {
+			return false;
+		}
+	}
+
 	@Nullable
 	@Override
 	public BackupMetadata getBackupMetadata(Transaction txn)
@@ -256,17 +288,97 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 					new BackupMetadata(secret, authors, threshold, 0);
 			BdfDictionary meta =
 					backupMetadataEncoder.encodeBackupMetadata(backupMetadata);
+
+			if (!db.containsGroup(txn, localGroup.getId()))
+				db.addGroup(txn, localGroup);
 			clientHelper.mergeGroupMetadata(txn, localGroup.getId(), meta);
 		} catch (FormatException e) {
 			throw new AssertionError(e);
 		}
 	}
 
-	private Group getContactGroup(Contact c) {
+	@Override
+	public Group getContactGroup(Contact c) {
 		return contactGroupFactory.createContactGroup(CLIENT_ID,
 				MAJOR_VERSION, c);
 	}
 
+	private ShardMessageHeader createShardMessageHeader(
+			Message message, BdfDictionary meta, MessageStatus status
+	)
+			throws FormatException {
+
+		boolean isLocal = meta.getBoolean(MSG_KEY_LOCAL);
+		boolean read = meta.getBoolean(MSG_KEY_READ, false);
+		long timestamp;
+		if (isLocal) {
+			timestamp = meta.getLong(MSG_KEY_TIMESTAMP);
+		} else {
+			timestamp = message.getTimestamp();
+		}
+		List<AttachmentHeader> attachmentHeaders =
+				new ArrayList<>();
+		return new ShardMessageHeader(
+				message.getId(), message.getGroupId(), timestamp,
+				isLocal, read, status.isSent(), status.isSeen(),
+				attachmentHeaders);
+	}
+
+	@Override
+	public Collection<ConversationMessageHeader> getMessageHeaders(
+			Transaction txn, ContactId contactId) throws DbException {
+		try {
+			Contact contact = db.getContact(txn, contactId);
+			GroupId contactGroupId = getContactGroup(contact).getId();
+			Map<MessageId, BdfDictionary> messages = clientHelper
+					.getMessageMetadataAsDictionary(txn, contactGroupId);
+			List<ConversationMessageHeader> headers =
+					new ArrayList<>();
+			for (Entry<MessageId, BdfDictionary> messageEntry : messages
+					.entrySet()) {
+				BdfDictionary meta = messageEntry.getValue();
+				if (meta.getLong(MSG_KEY_MESSAGE_TYPE).intValue() ==
+						SHARD.getValue()) {
+					Message message = clientHelper
+							.getMessage(txn, messageEntry.getKey());
+					MessageStatus status = db.getMessageStatus(txn, contactId,
+							messageEntry.getKey());
+					headers.add(createShardMessageHeader(message, meta, status));
+				}
+			}
+			return headers;
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	@Override
+	public Set<MessageId> getMessageIds(Transaction txn, ContactId contactId)
+			throws DbException {
+		Contact contact = db.getContact(txn, contactId);
+		GroupId contactGroupId = getContactGroup(contact).getId();
+		try {
+			Map<MessageId, BdfDictionary> messages = clientHelper
+					.getMessageMetadataAsDictionary(txn, contactGroupId);
+			return messages.keySet();
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	@Override
+	public DeletionResult deleteAllMessages(Transaction txn, ContactId c)
+			throws DbException {
+		return null;
+	}
+
+	@Override
+	public DeletionResult deleteMessages(Transaction txn, ContactId c,
+			Set<MessageId> messageIds) throws DbException {
+		DeletionResult result = new DeletionResult();
+		return result;
+	}
+
 	private void setContactId(Transaction txn, GroupId g, ContactId c)
 			throws DbException {
 		BdfDictionary d = new BdfDictionary();
@@ -323,14 +435,19 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 
 	private void sendShardMessage(Transaction txn, Contact custodian,
 			Shard shard) throws DbException, FormatException {
-		GroupId g = getContactGroup(custodian).getId();
+		Group group = getContactGroup(custodian);
+		GroupId g = group.getId();
+		if (!db.containsGroup(txn, g)) db.addGroup(txn, group);
 		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));
+				new BdfEntry(MSG_KEY_LOCAL, true),
+				new BdfEntry(MSG_KEY_TIMESTAMP, timestamp)
+		);
 		clientHelper.addLocalMessage(txn, m, meta, true, false);
+		messageTracker.trackOutgoingMessage(txn, m);
 	}
 
 	private void sendBackupMessage(Transaction txn, Contact custodian,
@@ -343,12 +460,17 @@ class SocialBackupManagerImpl extends BdfIncomingMessageHook
 		BdfDictionary meta = BdfDictionary.of(
 				new BdfEntry(MSG_KEY_MESSAGE_TYPE, BACKUP.getValue()),
 				new BdfEntry(MSG_KEY_LOCAL, true),
+				new BdfEntry(MSG_KEY_TIMESTAMP, timestamp),
 				new BdfEntry(MSG_KEY_VERSION, version));
 		clientHelper.addLocalMessage(txn, m, meta, true, false);
 	}
 
-	private boolean localBackupExists(Transaction txn) throws DbException {
+	private boolean localBackupExists(Transaction txn) {
-		return !db.getGroupMetadata(txn, localGroup.getId()).isEmpty();
+		try {
+			return !db.getGroupMetadata(txn, localGroup.getId()).isEmpty();
+		} catch (DbException e) {
+			return false;
+		}
 	}
 
 	@Nullable

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

@@ -7,7 +7,7 @@ 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.conversation.ConversationManager;
 import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 
 import javax.inject.Inject;
@@ -37,13 +37,15 @@ public class SocialBackupModule {
 			ContactManager contactManager,
 			ValidationManager validationManager,
 			ClientVersioningManager clientVersioningManager,
-			SocialBackupManagerImpl socialBackupManager) {
+			SocialBackupManagerImpl socialBackupManager,
+			ConversationManager conversationManager) {
 		lifecycleManager.registerOpenDatabaseHook(socialBackupManager);
 		contactManager.registerContactHook(socialBackupManager);
 		validationManager.registerIncomingMessageHook(CLIENT_ID,
 				MAJOR_VERSION, socialBackupManager);
 		clientVersioningManager.registerClient(CLIENT_ID, MAJOR_VERSION,
 				MINOR_VERSION, socialBackupManager);
+		conversationManager.registerConversationClient(socialBackupManager);
 		return socialBackupManager;
 	}
 
@@ -88,10 +90,4 @@ public class SocialBackupModule {
 	MessageParser messageParser(MessageParserImpl messageParser) {
 		return messageParser;
 	}
-
-	@Provides
-	DarkCrystal darkCrystal(DarkCrystalStub darkCrystal) {
-		// TODO: Replace this with a real implementation
-		return darkCrystal;
-	}
 }

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

@@ -3,6 +3,7 @@ package org.briarproject.briar.introduction;
 import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
 import org.briarproject.briar.BriarCoreModule;
+import org.briarproject.briar.socialbackup.DefaultDarkCrystalModule;
 import org.briarproject.briar.test.BriarIntegrationTestComponent;
 
 import javax.inject.Singleton;
@@ -13,7 +14,8 @@ import dagger.Component;
 @Component(modules = {
 		BrambleCoreIntegrationTestModule.class,
 		BrambleCoreModule.class,
-		BriarCoreModule.class
+		BriarCoreModule.class,
+		DefaultDarkCrystalModule.class
 })
 interface IntroductionIntegrationTestComponent
 		extends BriarIntegrationTestComponent {

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

@@ -1,8 +1,14 @@
 package org.briarproject.briar.socialbackup;
 
+import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.test.TestDatabaseConfigModule;
+import org.briarproject.briar.api.client.MessageTracker;
+import org.briarproject.briar.api.conversation.ConversationMessageHeader;
 import org.briarproject.briar.api.socialbackup.BackupMetadata;
+import org.briarproject.briar.api.socialbackup.ShardMessageHeader;
 import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 import org.briarproject.briar.test.BriarIntegrationTest;
 import org.briarproject.briar.test.BriarIntegrationTestComponent;
@@ -10,23 +16,40 @@ import org.briarproject.briar.test.DaggerBriarIntegrationTestComponent;
 import org.junit.Before;
 import org.junit.Test;
 
+import java.util.Collection;
 import java.util.List;
 
 import static java.util.Arrays.asList;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 public class SocialBackupIntegrationTest
 		extends BriarIntegrationTest<BriarIntegrationTestComponent> {
 
 	private SocialBackupManager socialBackupManager0;
+	private SocialBackupManager socialBackupManager1;
+	private SocialBackupManager socialBackupManager2;
+
+	private Group g1From0;
+	private Group g0From1;
+	private Group g2From0;
+	private Group g0From2;
 
 	@Before
 	@Override
 	public void setUp() throws Exception {
 		super.setUp();
 		socialBackupManager0 = c0.getSocialBackupManager();
+		socialBackupManager1 = c1.getSocialBackupManager();
+		socialBackupManager2 = c2.getSocialBackupManager();
+
+		g1From0 = socialBackupManager0.getContactGroup(contact1From0);
+		g0From1 = socialBackupManager1.getContactGroup(contact0From1);
+		g2From0 = socialBackupManager0.getContactGroup(contact2From0);
+		g0From2 = socialBackupManager2.getContactGroup(contact0From2);
 	}
 
 	@Override
@@ -71,5 +94,89 @@ public class SocialBackupIntegrationTest
 		// Sync the shard and backup messages to the contacts
 		sync0To1(2, true);
 		sync0To2(2, true);
+
+		Collection<ConversationMessageHeader> messages1At0 =
+				getMessages1At0();
+		assertEquals(1, messages1At0.size());
+		for (ConversationMessageHeader h : messages1At0) {
+			assertTrue(h instanceof ShardMessageHeader);
+			ShardMessageHeader s = (ShardMessageHeader) h;
+			assertTrue(s.isLocal());
+		}
+
+		Collection<ConversationMessageHeader> messages2At0 =
+				getMessages2At0();
+		assertEquals(1, messages2At0.size());
+		for (ConversationMessageHeader h : messages2At0) {
+			assertTrue(h instanceof ShardMessageHeader);
+			ShardMessageHeader s = (ShardMessageHeader) h;
+			assertTrue(s.isLocal());
+		}
+
+		// the shard message from 0 should have arrived at 1
+		Collection<ConversationMessageHeader> messages0At1 =
+				getMessages0At1();
+		assertEquals(1, messages0At1.size());
+		for (ConversationMessageHeader h : messages0At1) {
+			assertTrue(h instanceof ShardMessageHeader);
+			ShardMessageHeader s = (ShardMessageHeader) h;
+			assertFalse(s.isLocal());
+		}
+        db1.transaction(false, txn -> {
+        	assertTrue(socialBackupManager1.amCustodian(txn, contactId0From1));
+        });
+
+		// the shard message from 0 should have arrived at 2
+		Collection<ConversationMessageHeader> messages0At2 =
+				getMessages0At2();
+		assertEquals(1, messages0At2.size());
+		for (ConversationMessageHeader h : messages0At2) {
+			assertTrue(h instanceof ShardMessageHeader);
+			ShardMessageHeader s = (ShardMessageHeader) h;
+			assertFalse(s.isLocal());
+		}
+
+		// assert group counts
+		assertGroupCount(messageTracker0, g1From0.getId(), 1, 0);
+		assertGroupCount(messageTracker0, g2From0.getId(), 1, 0);
+		assertGroupCount(messageTracker1, g0From1.getId(), 1, 1);
+		assertGroupCount(messageTracker2, g0From2.getId(), 1, 1);
+
+		// mark a message as read
+		socialBackupManager1.setReadFlag(g0From1.getId(),
+				messages0At1.iterator().next().getId(), true);
+		assertGroupCount(messageTracker1, g0From1.getId(), 1, 0);
 	}
+
+	private Collection<ConversationMessageHeader> getMessages1At0()
+			throws DbException {
+		return db0.transactionWithResult(true, txn -> socialBackupManager0
+				.getMessageHeaders(txn, contactId1From0));
+	}
+
+	private Collection<ConversationMessageHeader> getMessages2At0()
+			throws DbException {
+		return db0.transactionWithResult(true, txn -> socialBackupManager0
+				.getMessageHeaders(txn, contactId2From0));
+	}
+
+	private Collection<ConversationMessageHeader> getMessages0At1()
+			throws DbException {
+		return db1.transactionWithResult(true, txn -> socialBackupManager1
+				.getMessageHeaders(txn, contactId0From1));
+	}
+
+	private Collection<ConversationMessageHeader> getMessages0At2()
+			throws DbException {
+		return db1.transactionWithResult(true, txn -> socialBackupManager2
+				.getMessageHeaders(txn, contactId0From2));
+	}
+
+	public static void assertGroupCount(MessageTracker tracker, GroupId g,
+			long msgCount, long unreadCount) throws DbException {
+		MessageTracker.GroupCount c1 = tracker.getGroupCount(g);
+		assertEquals(msgCount, c1.getMsgCount());
+		assertEquals(unreadCount, c1.getUnreadCount());
+	}
+
 }

briar-core/src/test/java/org/briarproject/briar/test/BriarIntegrationTestComponent.java

@@ -37,6 +37,7 @@ 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.DefaultDarkCrystalModule;
 import org.briarproject.briar.socialbackup.SocialBackupModule;
 
 import javax.inject.Singleton;
@@ -47,7 +48,8 @@ import dagger.Component;
 @Component(modules = {
 		BrambleCoreIntegrationTestModule.class,
 		BrambleCoreModule.class,
-		BriarCoreModule.class
+		BriarCoreModule.class,
+		DefaultDarkCrystalModule.class
 })
 public interface BriarIntegrationTestComponent
 		extends BrambleCoreIntegrationTestEagerSingletons {

briar-headless/src/main/java/org/briarproject/briar/headless/HeadlessModule.kt

@@ -28,6 +28,7 @@ import org.briarproject.briar.headless.contact.HeadlessContactModule
 import org.briarproject.briar.headless.event.HeadlessEventModule
 import org.briarproject.briar.headless.forums.HeadlessForumModule
 import org.briarproject.briar.headless.messaging.HeadlessMessagingModule
+import org.briarproject.briar.socialbackup.DefaultDarkCrystalModule
 import java.io.File
 import java.util.Collections.emptyList
 import javax.inject.Singleton
@@ -37,6 +38,7 @@ import javax.inject.Singleton
         AccountModule::class,
         CircumventionModule::class,
         DefaultBatteryManagerModule::class,
+        DefaultDarkCrystalModule::class, // FIXME: Real implementation needed
         DefaultEventExecutorModule::class,
         DefaultTaskSchedulerModule::class,
         DefaultWakefulIoExecutorModule::class,

briar-headless/src/main/java/org/briarproject/briar/headless/messaging/MessagingControllerImpl.kt

@@ -11,9 +11,9 @@ import org.briarproject.bramble.api.db.DatabaseExecutor
 import org.briarproject.bramble.api.db.NoSuchContactException
 import org.briarproject.bramble.api.event.Event
 import org.briarproject.bramble.api.event.EventListener
+import org.briarproject.bramble.api.sync.MessageId
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent
-import org.briarproject.bramble.api.sync.MessageId
 import org.briarproject.bramble.api.system.Clock
 import org.briarproject.bramble.util.StringUtils.utf8IsTooLong
 import org.briarproject.briar.api.blog.BlogInvitationRequest
@@ -31,6 +31,7 @@ import org.briarproject.briar.api.messaging.PrivateMessageFactory
 import org.briarproject.briar.api.messaging.PrivateMessageHeader
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationResponse
+import org.briarproject.briar.api.socialbackup.ShardMessageHeader
 import org.briarproject.briar.headless.event.WebSocketController
 import org.briarproject.briar.headless.event.output
 import org.briarproject.briar.headless.getContactIdFromPathParam
@@ -169,4 +170,6 @@ private class JsonVisitor(
     override fun visitIntroductionRequest(r: IntroductionRequest) = r.output(contactId)
 
     override fun visitIntroductionResponse(r: IntroductionResponse) = r.output(contactId)
+
+    override fun visitShardMessage(r: ShardMessageHeader) = r.output(contactId)
 }

briar-headless/src/test/java/org/briarproject/briar/headless/HeadlessTestModule.kt

@@ -24,6 +24,7 @@ import org.briarproject.briar.headless.contact.HeadlessContactModule
 import org.briarproject.briar.headless.event.HeadlessEventModule
 import org.briarproject.briar.headless.forums.HeadlessForumModule
 import org.briarproject.briar.headless.messaging.HeadlessMessagingModule
+import org.briarproject.briar.socialbackup.DefaultDarkCrystalModule
 import java.io.File
 import java.util.Collections.emptyList
 import javax.inject.Singleton
@@ -34,6 +35,7 @@ import javax.inject.Singleton
         JavaSystemModule::class,
         AccountModule::class,
         CircumventionModule::class,
+        DefaultDarkCrystalModule::class,
         DefaultEventExecutorModule::class,
         DefaultTaskSchedulerModule::class,
         DefaultWakefulIoExecutorModule::class,