Improve existing backup fragment

Social backup restore activity

See merge request briar/briar!1444

.idea/codeStyles/Project.xml

@@ -31,15 +31,6 @@
       <option name="PACKAGES_TO_USE_STAR_IMPORTS">
         <value />
       </option>
-      <option name="PACKAGES_IMPORT_LAYOUT">
-        <value>
-          <package name="" alias="false" withSubpackages="true" />
-          <package name="java" alias="false" withSubpackages="true" />
-          <package name="javax" alias="false" withSubpackages="true" />
-          <package name="kotlin" alias="false" withSubpackages="true" />
-          <package name="" alias="true" withSubpackages="true" />
-        </value>
-      </option>
       <option name="NAME_COUNT_TO_USE_STAR_IMPORT" value="2147483647" />
       <option name="NAME_COUNT_TO_USE_STAR_IMPORT_FOR_MEMBERS" value="2147483647" />
       <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />

bramble-android/build.gradle

@@ -50,10 +50,10 @@ dependencies {
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
-	testImplementation 'junit:junit:4.12'
-	testImplementation "org.jmock:jmock:2.8.2"
-	testImplementation "org.jmock:jmock-junit4:2.8.2"
-	testImplementation "org.jmock:jmock-legacy:2.8.2"
+	testImplementation "junit:junit:$junit_version"
+	testImplementation "org.jmock:jmock:$jmock_version"
+	testImplementation "org.jmock:jmock-junit4:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 }
 
 def torBinariesDir = 'src/main/res/raw'

bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java

@@ -9,7 +9,7 @@ import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -44,7 +44,7 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 	private AndroidAccountManager accountManager;
 
 	public AndroidAccountManagerTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		app = context.mock(Application.class);
 		applicationInfo = new ApplicationInfo();
 		applicationInfo.dataDir = testDir.getAbsolutePath();

bramble-android/witness.gradle

@@ -1,6 +1,6 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
+        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
         'com.android.tools.analytics-library:protos:27.1.1:protos-27.1.1.jar:13f77e73762e58ab372d140b3a6be6903aea9775b62dd14fbc62d4cc7069c9a4',
         'com.android.tools.analytics-library:shared:27.1.1:shared-27.1.1.jar:82930a52001410e97d809930b670f4de3002286975f046b9de5f6b777b06d366',
         'com.android.tools.analytics-library:tracker:27.1.1:tracker-27.1.1.jar:31bc5a00be0055bac89c9b2f34751883e987cd89e3ac1783720645c164f591d9',
@@ -31,6 +31,7 @@ dependencyVerification {
         'com.android.tools:sdklib:27.1.1:sdklib-27.1.1.jar:08e6b83961ac9724b3c1e3d0eff971f13be6701292c77914b8794480f3391250',
         'com.android:signflinger:4.1.1:signflinger-4.1.1.jar:0c66825988873ec2d51057fa463f54a8f18fc7326ff4530b9da363b71e97ce60',
         'com.android:zipflinger:4.1.1:zipflinger-4.1.1.jar:0a8c3e52ac13dd031236f9fb5ba4408b1d5dcd12325a05440b36da09d8881446',
+        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.code.gson:gson:2.8.5:gson-2.8.5.jar:233a0149fc365c9f6edbd683cfe266b19bdc773be98eabdaf6b3c924b48e7d81',
         'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
@@ -63,16 +64,16 @@ dependencyVerification {
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'javax.xml.bind:jaxb-api:2.3.1:jaxb-api-2.3.1.jar:88b955a0df57880a26a74708bc34f74dcaf8ebf4e78843a28b50eae945732b06',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
+        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
+        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
         'net.sf.jopt-simple:jopt-simple:4.9:jopt-simple-4.9.jar:26c5856e954b5f864db76f13b86919b59c6eecf9fd930b96baa8884626baf2f5',
         'net.sf.kxml:kxml2:2.3.0:kxml2-2.3.0.jar:f264dd9f79a1fde10ce5ecc53221eff24be4c9331c830b7d52f2f08a7b633de2',
-        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
-        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
+        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
         'org.apache.commons:commons-compress:1.12:commons-compress-1.12.jar:2c1542faf343185b7cab9c3d55c8ae5471d6d095d3887a4adefdbdf2984dc0b6',
         'org.apache.httpcomponents:httpclient:4.5.6:httpclient-4.5.6.jar:c03f813195e7a80e3608d0ddd8da80b21696a4c92a6a2298865bf149071551c7',
         'org.apache.httpcomponents:httpcore:4.4.10:httpcore-4.4.10.jar:78ba1096561957db1b55200a159b648876430342d15d461277e62360da19f6fd',
         'org.apache.httpcomponents:httpmime:4.5.6:httpmime-4.5.6.jar:0b2b1102c18d3c7e05a77214b9b7501a6f6056174ae5604e0e256776eda7553e',
-        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.bouncycastle:bcpkix-jdk15on:1.56:bcpkix-jdk15on-1.56.jar:7043dee4e9e7175e93e0b36f45b1ec1ecb893c5f755667e8b916eb8dd201c6ca',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
         'org.briarproject:obfs4proxy-android:0.0.12-dev-40245c4a:obfs4proxy-android-0.0.12-dev-40245c4a.zip:8ab05a8f8391be2cb5ab2b665c281a06d9e3a756bd0f95a40a36ca927866ea82',
@@ -85,8 +86,9 @@ dependencyVerification {
         'org.codehaus.mojo:animal-sniffer-annotations:1.18:animal-sniffer-annotations-1.18.jar:47f05852b48ee9baefef80fa3d8cea60efa4753c0013121dd7fe5eef2e5c729d',
         'org.glassfish.jaxb:jaxb-runtime:2.3.1:jaxb-runtime-2.3.1.jar:45fecfa5c8217ce1f3652ab95179790ec8cc0dec0384bca51cbeb94a293d9f2f',
         'org.glassfish.jaxb:txw2:2.3.1:txw2-2.3.1.jar:34975dde1c6920f1a39791142235689bc3cd357e24d05edd8ff93b885bd68d60',
-        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
-        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
+        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
+        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
+        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
         'org.jetbrains.kotlin:kotlin-reflect:1.3.72:kotlin-reflect-1.3.72.jar:a188d9367de1c4ee9479db630985c0597b20709c83161b1430d24edb27e38c40',
         'org.jetbrains.kotlin:kotlin-stdlib-common:1.3.72:kotlin-stdlib-common-1.3.72.jar:5e7d1552863e480c1628b1cc39ce230ef829f5b7230106215a05acda5172203a',
         'org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.72:kotlin-stdlib-jdk7-1.3.72.jar:40566c0c08d414b9413ba556ff7f8a0b04b98b9f0f424d122dd2088510efccc4',
@@ -94,17 +96,18 @@ dependencyVerification {
         'org.jetbrains.kotlin:kotlin-stdlib:1.3.72:kotlin-stdlib-1.3.72.jar:3856a7349ebacd6d1be6802b2fed9c4dc2c5a564ea92b6b945ac988243d4b16b',
         'org.jetbrains.trove4j:trove4j:20160824:trove4j-20160824.jar:1917871c8deb468307a584680c87a44572f5a8b0b98c6d397fc0f5f86596dbe7',
         'org.jetbrains:annotations:13.0:annotations-13.0.jar:ace2a10dc8e2d5fd34925ecac03e4988b2c0f851650c94b8cef49ba1bd111478',
-        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
-        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
-        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
-        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
+        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
+        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
+        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
+        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
+        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
         'org.jvnet.staxex:stax-ex:1.8:stax-ex-1.8.jar:95b05d9590af4154c6513b9c5dc1fb2e55b539972ba0a9ef28e9a0c01d83ad77',
-        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
+        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
         'org.ow2.asm:asm-analysis:7.0:asm-analysis-7.0.jar:e981f8f650c4d900bb033650b18e122fa6b161eadd5f88978d08751f72ee8474',
         'org.ow2.asm:asm-commons:7.0:asm-commons-7.0.jar:fed348ef05958e3e846a3ac074a12af5f7936ef3d21ce44a62c4fa08a771927d',
         'org.ow2.asm:asm-tree:7.0:asm-tree-7.0.jar:cfd7a0874f9de36a999c127feeadfbfe6e04d4a71ee954d7af3d853f0be48a6c',
         'org.ow2.asm:asm-util:7.0:asm-util-7.0.jar:75fbbca440ef463f41c2b0ab1a80abe67e910ac486da60a7863cbcb5bae7e145',
-        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
         'org.ow2.asm:asm:7.0:asm-7.0.jar:b88ef66468b3c978ad0c97fd6e90979e56155b4ac69089ba7a44e9aa7ffe9acf',
+        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
     ]
 }

bramble-api/build.gradle

@@ -10,10 +10,9 @@ dependencies {
 	implementation "com.google.dagger:dagger:2.24"
 	implementation 'com.google.code.findbugs:jsr305:3.0.2'
 
-	testImplementation 'junit:junit:4.12'
-	testImplementation "org.jmock:jmock:2.8.2"
-	testImplementation "org.jmock:jmock-junit4:2.8.2"
-	testImplementation "org.jmock:jmock-legacy:2.8.2"
+	testImplementation "junit:junit:$junit_version"
+	testImplementation "org.jmock:jmock:$jmock_version"
+	testImplementation "org.jmock:jmock-junit4:$jmock_version"
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

bramble-api/src/main/java/org/briarproject/bramble/api/account/AccountManager.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.api.account;
 
 import org.briarproject.bramble.api.crypto.DecryptionException;
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
@@ -43,6 +44,17 @@ public interface AccountManager {
 	 */
 	boolean createAccount(String name, String password);
 
+	/**
+	 * Restores a given identity by registering it with the
+	 * {@link IdentityManager}.  Creates a database key, encrypts it with the
+	 * given password and stores it on disk. {@link #accountExists()} will
+	 * return true after this method returns true.
+ 	 * @param identity
+	 * @param password
+	 * @return
+	 */
+	boolean restoreAccount(Identity identity, String password);
+
 	/**
 	 * Deletes all account state from disk. {@link #accountExists()} will
 	 * return false after this method returns.

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactExchangeConstants.java

@@ -1,6 +1,6 @@
-package org.briarproject.bramble.contact;
+package org.briarproject.bramble.api.contact;
 
-interface ContactExchangeConstants {
+public interface ContactExchangeConstants {
 
 	/**
 	 * The current version of the contact exchange protocol.

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactExchangeCrypto.java

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.contact;
+package org.briarproject.bramble.api.contact;
 
 import org.briarproject.bramble.api.crypto.PrivateKey;
 import org.briarproject.bramble.api.crypto.PublicKey;
@@ -6,7 +6,7 @@ import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 @NotNullByDefault
-interface ContactExchangeCrypto {
+public interface ContactExchangeCrypto {
 
 	/**
 	 * Derives the header key for a contact exchange stream from the master key.

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactExchangeRecordTypes.java

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api.contact;
+
+/**
+ * Record types for the contact exchange protocol.
+ */
+public interface ContactExchangeRecordTypes {
+
+	byte CONTACT_INFO = 0;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactManager.java

@@ -3,6 +3,7 @@ package org.briarproject.bramble.api.contact;
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.UnsupportedVersionException;
+import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DbException;
@@ -48,6 +49,10 @@ public interface ContactManager {
 			SecretKey rootKey, long timestamp, boolean alice, boolean verified,
 			boolean active) throws DbException;
 
+	ContactId addContact(Transaction txn, Author remote, AuthorId local,
+			PublicKey handshake, boolean verified)
+			throws DbException, GeneralSecurityException;
+
 	/**
 	 * Stores a contact associated with the given local and remote pseudonyms,
 	 * replacing the given pending contact, derives and stores handshake mode
@@ -205,6 +210,19 @@ public interface ContactManager {
 	void setContactAlias(ContactId c, @Nullable String alias)
 			throws DbException;
 
+	/**
+	 * Sets the contact's handshake public key
+	 */
+	void setHandshakePublicKey(Transaction txn, ContactId c,
+			PublicKey handshakePublicKey) throws DbException,
+			GeneralSecurityException;
+
+	/**
+	 * Sets the contact's handshake public key
+	 */
+	void setHandshakePublicKey(ContactId c, PublicKey handshakePublicKey)
+			throws DbException, GeneralSecurityException;
+
 	/**
 	 * Returns true if a contact with this {@code remoteAuthorId} belongs to
 	 * the local pseudonym with this {@code localAuthorId}.

bramble-api/src/main/java/org/briarproject/bramble/api/contact/HandshakeManager.java

@@ -24,6 +24,19 @@ public interface HandshakeManager {
 	HandshakeResult handshake(PendingContactId p, InputStream in,
 			StreamWriter out) throws DbException, IOException;
 
+	/**
+	 * Handshakes with the given contact. Returns an ephemeral master key
+	 * authenticated with both parties' handshake key pairs and a flag
+	 * indicating whether the local peer is Alice or Bob.
+	 *
+	 * @param in An incoming stream for the handshake, which must be secured in
+	 * handshake mode
+	 * @param out An outgoing stream for the handshake, which must be secured
+	 * in handshake mode
+	 */
+	HandshakeResult handshake(ContactId c, InputStream in, StreamWriter out)
+			throws DbException, IOException;
+
 	class HandshakeResult {
 
 		private final SecretKey masterKey;

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

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

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -546,6 +546,11 @@ public interface DatabaseComponent extends TransactionManager {
 	void setContactAlias(Transaction txn, ContactId c, @Nullable String alias)
 			throws DbException;
 
+	/**
+	 * Sets the remote handshake public key for a given contact
+	 */
+	void setHandshakePublicKey(Transaction txn, ContactId c, PublicKey handshakePublicKey) throws DbException;
+
 	/**
 	 * Sets the given group's visibility to the given contact.
 	 */

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

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

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

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

bramble-api/src/main/java/org/briarproject/bramble/api/transport/KeyManager.java

@@ -35,6 +35,20 @@ public interface KeyManager {
 			ContactId c, SecretKey rootKey, long timestamp, boolean alice,
 			boolean active) throws DbException;
 
+	/**
+	 * Derives and stores a set of rotation mode transport keys for
+	 * communicating with the given contact over each transport and returns the
+	 * key set IDs.
+	 * <p/>
+	 * {@link StreamContext StreamContexts} for the contact can be created
+	 * after this method has returned.
+	 *
+	 * @param alice True if the local party is Alice
+	 * @param active Whether the derived keys can be used for outgoing streams
+	 */
+	Map<TransportId, KeySetId> addRotationKeys(ContactId c, SecretKey rootKey,
+			long timestamp, boolean alice, boolean active) throws DbException;
+
 	/**
 	 * Informs the key manager that a new contact has been added. Derives and
 	 * stores a set of handshake mode transport keys for communicating with the

bramble-api/witness.gradle

@@ -1,24 +1,27 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
+        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
+        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
-        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
-        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
-        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
+        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
+        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
+        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
         'org.codehaus.mojo.signature:java16:1.1:java16-1.1.signature:53799223a2c98dba2d0add810bed76315460df285c69e4f397ae6098f87dd619',
         'org.codehaus.mojo:animal-sniffer-ant-tasks:1.16:animal-sniffer-ant-tasks-1.16.jar:890040976fbe2d584619a6a61b1fd2e925b3b5eb342a85eb2762c467c0d64e90',
         'org.codehaus.mojo:animal-sniffer:1.16:animal-sniffer-1.16.jar:72be8bcc226ba43b937c722a08a07852bfa1b11400089265d5df0ee7b38b1d52',
-        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
-        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
-        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
-        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
-        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
-        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
-        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
+        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
+        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
+        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
+        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
+        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
+        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
+        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
+        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
+        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
         'org.ow2.asm:asm-all:5.2:asm-all-5.2.jar:7fbffbc1db3422e2101689fd88df8384b15817b52b9b2b267b9f6d2511dc198d',
-        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
+        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
     ]
 }

bramble-core/build.gradle

@@ -21,16 +21,25 @@ dependencies {
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation 'org.hsqldb:hsqldb:2.3.5' // The last version that supports Java 1.6
-	testImplementation 'junit:junit:4.12'
-	testImplementation "org.jmock:jmock:2.8.2"
-	testImplementation "org.jmock:jmock-junit4:2.8.2"
-	testImplementation "org.jmock:jmock-legacy:2.8.2"
+	testImplementation 'net.jodah:concurrentunit:0.4.2'
+	testImplementation "junit:junit:$junit_version"
+	testImplementation "org.jmock:jmock:$jmock_version"
+	testImplementation "org.jmock:jmock-junit4:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 
 	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }
 
+animalsniffer {
+	// Allow requireNonNull: Android desugaring rewrites it (so it's safe for us to use),
+	// and it gets used when passing method references instead of lambdas with Java 11.
+	// Note that this line allows *all* methods from java.util.Objects.
+	// That's the best that we can do with the configuration options that Animal Sniffer offers.
+	ignore 'java.util.Objects'
+}
+
 // needed to make test output available to bramble-java
 configurations {
 	testOutput.extendsFrom(testCompile)

bramble-core/src/main/java/org/briarproject/bramble/account/AccountManagerImpl.java

@@ -176,6 +176,18 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
+	public boolean restoreAccount(Identity identity, String password) {
+		synchronized (stateChangeLock) {
+			if (hasDatabaseKey())
+				throw new AssertionError("Already have a database key");
+			identityManager.registerIdentity(identity);
+			SecretKey key = crypto.generateSecretKey();
+			if (!encryptAndStoreDatabaseKey(key, password)) return false;
+			databaseKey = key;
+			return true;
+		}
+	}
+
 	@GuardedBy("stateChangeLock")
 	private boolean encryptAndStoreDatabaseKey(SecretKey key, String password) {
 		byte[] plaintext = key.getBytes();

bramble-core/src/main/java/org/briarproject/bramble/connection/ConnectionManagerImpl.java

@@ -76,7 +76,7 @@ class ConnectionManagerImpl implements ConnectionManager {
 		ioExecutor.execute(new IncomingDuplexSyncConnection(keyManager,
 				connectionRegistry, streamReaderFactory, streamWriterFactory,
 				syncSessionFactory, transportPropertyManager, ioExecutor,
-				t, d));
+				t, d, handshakeManager));
 	}
 
 	@Override
@@ -101,7 +101,7 @@ class ConnectionManagerImpl implements ConnectionManager {
 		ioExecutor.execute(new OutgoingDuplexSyncConnection(keyManager,
 				connectionRegistry, streamReaderFactory, streamWriterFactory,
 				syncSessionFactory, transportPropertyManager, ioExecutor,
-				secureRandom, c, t, d));
+				secureRandom, handshakeManager, c, t, d));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java

@@ -3,6 +3,7 @@ package org.briarproject.bramble.connection;
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.connection.InterruptibleConnection;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.HandshakeManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.connection;
 
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.HandshakeManager;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
@@ -13,9 +14,11 @@ import org.briarproject.bramble.api.sync.SyncSessionFactory;
 import org.briarproject.bramble.api.transport.KeyManager;
 import org.briarproject.bramble.api.transport.StreamContext;
 import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
 import org.briarproject.bramble.api.transport.StreamWriterFactory;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.concurrent.Executor;
 
 import static java.util.logging.Level.WARNING;
@@ -24,6 +27,10 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 @NotNullByDefault
 class IncomingDuplexSyncConnection extends DuplexSyncConnection
 		implements Runnable {
+	private final HandshakeManager handshakeManager;
+
+	// FIXME: Exchange timestamp as part of handshake protocol?
+	private static final long TIMESTAMP = 1617235200; // 1 April 2021 00:00 UTC
 
 	IncomingDuplexSyncConnection(KeyManager keyManager,
 			ConnectionRegistry connectionRegistry,
@@ -32,14 +39,18 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 			SyncSessionFactory syncSessionFactory,
 			TransportPropertyManager transportPropertyManager,
 			Executor ioExecutor, TransportId transportId,
-			DuplexTransportConnection connection) {
+			DuplexTransportConnection connection,
+			HandshakeManager handshakeManager) {
 		super(keyManager, connectionRegistry, streamReaderFactory,
 				streamWriterFactory, syncSessionFactory,
 				transportPropertyManager, ioExecutor, transportId, connection);
+		this.handshakeManager = handshakeManager;
 	}
 
 	@Override
 	public void run() {
+		LOG.info("Running IncomingDuplexSyncConnection on transport " +
+				transportId.getString());
 		// Read and recognise the tag
 		StreamContext ctx = recogniseTag(reader, transportId);
 		if (ctx == null) {
@@ -54,10 +65,22 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 			return;
 		}
 		if (ctx.isHandshakeMode()) {
-			// TODO: Support handshake mode for contacts
-			LOG.warning("Received handshake tag, expected rotation mode");
-			onReadError(true);
-			return;
+			if (!performHandshake(ctx, contactId)) {
+				LOG.warning("Handshake failed");
+				return;
+			}
+			// Allocate a rotation mode stream context
+			ctx = allocateStreamContext(contactId, transportId);
+			if (ctx == null) {
+				LOG.warning("Could not allocate stream context");
+				onWriteError();
+				return;
+			}
+			if (ctx.isHandshakeMode()) {
+				LOG.warning("Got handshake mode context after handshaking");
+				onWriteError();
+				return;
+			}
 		}
 		connectionRegistry.registerIncomingConnection(contactId, transportId,
 				this);
@@ -103,5 +126,35 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 			onWriteError();
 		}
 	}
+
+	private boolean performHandshake(StreamContext ctxIn, ContactId contactId) {
+		LOG.info("Performing handshake (Incoming)");
+		// Allocate the outgoing stream context
+		StreamContext ctxOut =
+				allocateStreamContext(contactId, transportId);
+		if (ctxOut == null) {
+			LOG.warning("Could not allocate stream context");
+			onReadError(true);
+			return false;
+		}
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			// Flush the output stream to send the outgoing stream header
+			StreamWriter out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+			HandshakeManager.HandshakeResult result =
+					handshakeManager.handshake(contactId, in, out);
+			keyManager.addRotationKeys(contactId, result.getMasterKey(),
+					TIMESTAMP, result.isAlice(), true);
+			LOG.info("Rotation keys added");
+			return true;
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onReadError(true);
+			return false;
+		}
+	}
 }
 

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.connection;
 
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.HandshakeManager;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
@@ -14,9 +15,11 @@ import org.briarproject.bramble.api.sync.SyncSessionFactory;
 import org.briarproject.bramble.api.transport.KeyManager;
 import org.briarproject.bramble.api.transport.StreamContext;
 import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
 import org.briarproject.bramble.api.transport.StreamWriterFactory;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
 
@@ -28,26 +31,38 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 		implements Runnable {
 
+	// FIXME: Exchange timestamp as part of handshake protocol?
+	private static final long TIMESTAMP = 1617235200; // 1 April 2021 00:00 UTC
+
 	private final SecureRandom secureRandom;
+	private final HandshakeManager handshakeManager;
 	private final ContactId contactId;
 
-	OutgoingDuplexSyncConnection(KeyManager keyManager,
+	OutgoingDuplexSyncConnection(
+			KeyManager keyManager,
 			ConnectionRegistry connectionRegistry,
 			StreamReaderFactory streamReaderFactory,
 			StreamWriterFactory streamWriterFactory,
 			SyncSessionFactory syncSessionFactory,
 			TransportPropertyManager transportPropertyManager,
-			Executor ioExecutor, SecureRandom secureRandom, ContactId contactId,
-			TransportId transportId, DuplexTransportConnection connection) {
+			Executor ioExecutor,
+			SecureRandom secureRandom,
+			HandshakeManager handshakeManager,
+			ContactId contactId,
+			TransportId transportId,
+			DuplexTransportConnection connection) {
 		super(keyManager, connectionRegistry, streamReaderFactory,
 				streamWriterFactory, syncSessionFactory,
 				transportPropertyManager, ioExecutor, transportId, connection);
 		this.secureRandom = secureRandom;
+		this.handshakeManager = handshakeManager;
 		this.contactId = contactId;
 	}
 
 	@Override
 	public void run() {
+		LOG.info("Running OutgoingDuplexSyncConnection on transport " +
+				transportId.getString());
 		// Allocate a stream context
 		StreamContext ctx = allocateStreamContext(contactId, transportId);
 		if (ctx == null) {
@@ -56,10 +71,22 @@ class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 			return;
 		}
 		if (ctx.isHandshakeMode()) {
-			// TODO: Support handshake mode for contacts
-			LOG.warning("Cannot use handshake mode stream context");
-			onWriteError();
-			return;
+			if (!performHandshake(ctx)) {
+				LOG.warning("Handshake failed");
+				return;
+			}
+			// Allocate a rotation mode stream context
+			ctx = allocateStreamContext(contactId, transportId);
+			if (ctx == null) {
+				LOG.warning("Could not allocate stream context");
+				onWriteError();
+				return;
+			}
+			if (ctx.isHandshakeMode()) {
+				LOG.warning("Got handshake mode context after handshaking");
+				onWriteError();
+				return;
+			}
 		}
 		// Start the incoming session on another thread
 		Priority priority = generatePriority();
@@ -127,6 +154,59 @@ class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 		}
 	}
 
+	private boolean performHandshake(StreamContext ctxOut) {
+		LOG.info("Performing handshake (Outgoing)");
+		// Flush the output stream to send the outgoing stream header
+		StreamWriter out;
+		try {
+			out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+			return false;
+		}
+		// Read and recognise the tag
+		StreamContext ctxIn = recogniseTag(reader, transportId);
+		// Unrecognised tags are suspicious in this case
+		if (ctxIn == null) {
+			LOG.warning("Unrecognised tag for returning stream");
+			onReadError();
+			return false;
+		}
+		// Check that the stream comes from the expected contact
+		ContactId inContactId = ctxIn.getContactId();
+		if (contactId == null) {
+			LOG.warning("Expected contact tag, got rendezvous tag");
+			onReadError();
+			return false;
+		}
+		if (!inContactId.equals(contactId)) {
+			LOG.warning("Wrong contact ID for returning stream");
+			onReadError();
+			return false;
+		}
+		// TODO: Register the connection, close it if it's redundant
+		// Handshake and exchange contacts
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			HandshakeManager.HandshakeResult result =
+					handshakeManager.handshake(contactId, in, out);
+			keyManager.addRotationKeys(contactId, result.getMasterKey(),
+					TIMESTAMP, result.isAlice(), true);
+			LOG.info("Rotation keys added");
+			return true;
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+			return false;
+		} finally {
+			// TODO: Unregister the connection
+		}
+	}
+
 	private void onReadError() {
 		// 'Recognised' is always true for outgoing connections
 		onReadError(true);

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeCryptoImpl.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.contact;
 
+import org.briarproject.bramble.api.contact.ContactExchangeCrypto;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.PrivateKey;
 import org.briarproject.bramble.api.crypto.PublicKey;
@@ -10,12 +11,12 @@ import java.security.GeneralSecurityException;
 
 import javax.inject.Inject;
 
-import static org.briarproject.bramble.contact.ContactExchangeConstants.ALICE_KEY_LABEL;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.ALICE_NONCE_LABEL;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.BOB_KEY_LABEL;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.BOB_NONCE_LABEL;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.PROTOCOL_VERSION;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.SIGNING_LABEL;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.ALICE_KEY_LABEL;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.ALICE_NONCE_LABEL;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.BOB_KEY_LABEL;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.BOB_NONCE_LABEL;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.SIGNING_LABEL;
 
 @NotNullByDefault
 class ContactExchangeCryptoImpl implements ContactExchangeCrypto {

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeManagerImpl.java

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.Predicate;
 import org.briarproject.bramble.api.client.ClientHelper;
 import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactExchangeCrypto;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
@@ -47,8 +48,8 @@ import javax.inject.Inject;
 
 import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_SIGNATURE_LENGTH;
-import static org.briarproject.bramble.contact.ContactExchangeConstants.PROTOCOL_VERSION;
-import static org.briarproject.bramble.contact.ContactExchangeRecordTypes.CONTACT_INFO;
+import static org.briarproject.bramble.api.contact.ContactExchangeConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.api.contact.ContactExchangeRecordTypes.CONTACT_INFO;
 import static org.briarproject.bramble.util.ValidationUtils.checkLength;
 import static org.briarproject.bramble.util.ValidationUtils.checkSize;
 
@@ -81,7 +82,8 @@ class ContactExchangeManagerImpl implements ContactExchangeManager {
 	private final ContactManager contactManager;
 	private final IdentityManager identityManager;
 	private final TransportPropertyManager transportPropertyManager;
-	private final ContactExchangeCrypto contactExchangeCrypto;
+	private final org.briarproject.bramble.api.contact.ContactExchangeCrypto
+			contactExchangeCrypto;
 	private final StreamReaderFactory streamReaderFactory;
 	private final StreamWriterFactory streamWriterFactory;
 

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeRecordTypes.java

@@ -1,9 +0,0 @@
-package org.briarproject.bramble.contact;
-
-/**
- * Record types for the contact exchange protocol.
- */
-interface ContactExchangeRecordTypes {
-
-	byte CONTACT_INFO = 0;
-}

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -9,6 +9,7 @@ import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.contact.PendingContactState;
 import org.briarproject.bramble.api.contact.event.PendingContactStateChangedEvent;
+import org.briarproject.bramble.api.crypto.CryptoConstants;
 import org.briarproject.bramble.api.crypto.KeyPair;
 import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.crypto.SecretKey;
@@ -119,6 +120,18 @@ class ContactManagerImpl implements ContactManager, EventListener {
 						verified, active));
 	}
 
+	@Override
+	public ContactId addContact(Transaction txn, Author remote, AuthorId local,
+			PublicKey handshake, boolean verified)
+			throws DbException, GeneralSecurityException {
+		ContactId c = db.addContact(txn, remote, local, handshake, verified);
+		Contact contact = db.getContact(txn, c);
+		KeyPair ourKeyPair = identityManager.getHandshakeKeys(txn);
+		keyManager.addContact(txn, c, handshake, ourKeyPair);
+		for (ContactHook hook : hooks) hook.addingContact(txn, contact);
+		return c;
+	}
+
 	@Override
 	public String getHandshakeLink() throws DbException {
 		KeyPair keyPair = db.transactionWithResult(true,
@@ -234,6 +247,25 @@ class ContactManagerImpl implements ContactManager, EventListener {
 		db.transaction(false, txn -> setContactAlias(txn, c, alias));
 	}
 
+	@Override
+	public void setHandshakePublicKey(Transaction txn, ContactId c,
+			PublicKey handshakePublicKey) throws DbException, GeneralSecurityException {
+		if (handshakePublicKey.getKeyType() !=
+				CryptoConstants.KEY_TYPE_AGREEMENT) {
+			throw new IllegalArgumentException();
+		}
+		db.setHandshakePublicKey(txn, c, handshakePublicKey);
+		KeyPair ourKeyPair = identityManager.getHandshakeKeys(txn);
+		keyManager.addContact(txn, c, handshakePublicKey, ourKeyPair);
+	}
+
+	@Override
+	public void setHandshakePublicKey(ContactId c, PublicKey handshakePublicKey)
+			throws DbException, GeneralSecurityException {
+		db.transaction(false,
+				txn -> setHandshakePublicKey(txn, c, handshakePublicKey));
+	}
+
 	@Override
 	public boolean contactExists(Transaction txn, AuthorId remoteAuthorId,
 			AuthorId localAuthorId) throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactModule.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.contact;
 
+import org.briarproject.bramble.api.contact.ContactExchangeCrypto;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.contact.HandshakeManager;

bramble-core/src/main/java/org/briarproject/bramble/contact/HandshakeManagerImpl.java

@@ -3,6 +3,8 @@ package org.briarproject.bramble.contact;
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.Predicate;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.contact.HandshakeManager;
 import org.briarproject.bramble.api.contact.PendingContact;
@@ -88,6 +90,27 @@ class HandshakeManagerImpl implements HandshakeManager {
 		});
 		PublicKey theirStaticPublicKey = keys.getFirst();
 		KeyPair ourStaticKeyPair = keys.getSecond();
+		return handshake(theirStaticPublicKey, ourStaticKeyPair, in, out);
+	}
+
+	@Override
+	public HandshakeResult handshake(ContactId c, InputStream in,
+			StreamWriter out) throws DbException, IOException {
+		Pair<PublicKey, KeyPair> keys = db.transactionWithResult(true, txn -> {
+			Contact contact = contactManager.getContact(txn, c);
+			PublicKey handshakePublicKey = contact.getHandshakePublicKey();
+			if (handshakePublicKey == null) throw new DbException();
+			KeyPair keyPair = identityManager.getHandshakeKeys(txn);
+			return new Pair<>(handshakePublicKey, keyPair);
+		});
+		PublicKey theirStaticPublicKey = keys.getFirst();
+		KeyPair ourStaticKeyPair = keys.getSecond();
+		return handshake(theirStaticPublicKey, ourStaticKeyPair, in, out);
+	}
+
+	private HandshakeResult handshake(PublicKey theirStaticPublicKey,
+			KeyPair ourStaticKeyPair, InputStream in, StreamWriter out)
+			throws IOException {
 		boolean alice = transportCrypto.isAlice(theirStaticPublicKey,
 				ourStaticKeyPair);
 		RecordReader recordReader = recordReaderFactory.createRecordReader(in);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -32,6 +32,7 @@ import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeySet;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
+import java.sql.Connection;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
@@ -695,6 +696,11 @@ interface Database<T> {
 	void setHandshakeKeyPair(T txn, AuthorId local, PublicKey publicKey,
 			PrivateKey privateKey) throws DbException;
 
+	/**
+	 * Sets the handshake public key for a given contact
+	 */
+	void setHandshakePublicKey(T txn, ContactId c, PublicKey handshakePublicKey) throws DbException;
+
 	/**
 	 * Marks the given message as permanent, i.e. not temporary.
 	 */

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -1040,6 +1040,15 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		}
 	}
 
+	@Override
+	public void setHandshakePublicKey(Transaction transaction, ContactId c, PublicKey handshakePublicKey) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		db.setHandshakePublicKey(txn, c, handshakePublicKey);
+	}
+
 	@Override
 	public void setHandshakeKeyPair(Transaction transaction, AuthorId local,
 			PublicKey publicKey, PrivateKey privateKey) throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java

@@ -3058,6 +3058,23 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public void setHandshakePublicKey(Connection txn, ContactId c, PublicKey handshakePublicKey) throws DbException {
+		PreparedStatement ps = null;
+		try {
+			String sql = "UPDATE contacts SET handshakePublicKey = ? WHERE contactId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, handshakePublicKey.getEncoded());
+			ps.setInt(2, c.getInt());
+			int affected = ps.executeUpdate();
+			if (affected < 0 || affected > 1) throw new DbStateException();
+			ps.close();
+		} catch (SQLException e) {
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void setGroupVisibility(Connection txn, ContactId c, GroupId g,
 			boolean shared) throws DbException {

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

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

bramble-core/src/main/java/org/briarproject/bramble/keyagreement/KeyAgreementConnector.java

@@ -127,6 +127,7 @@ class KeyAgreementConnector {
 		List<Pair<DuplexPlugin, BdfList>> transports = new ArrayList<>();
 		for (TransportId id : PREFERRED_TRANSPORTS) {
 			TransportDescriptor d = descriptors.get(id);
+			LOG.info("id: " + id + " d: " + d);
 			Plugin p = pluginManager.getPlugin(id);
 			if (d != null && p instanceof DuplexPlugin) {
 				if (LOG.isLoggable(INFO))
@@ -137,6 +138,9 @@ class KeyAgreementConnector {
 
 		// TODO: If we don't have any transports in common with the peer,
 		//  warn the user and give up (#1224)
+        if (transports.isEmpty()) {
+           LOG.info("No transports found");
+        }
 
 		if (!transports.isEmpty()) {
 			byte[] commitment = remotePayload.getCommitment();

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

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

bramble-core/src/main/java/org/briarproject/bramble/transport/KeyManagerImpl.java

@@ -101,9 +101,9 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 	}
 
 	@Override
-	public Map<TransportId, KeySetId> addRotationKeys(
-			Transaction txn, ContactId c, SecretKey rootKey, long timestamp,
-			boolean alice, boolean active) throws DbException {
+	public Map<TransportId, KeySetId> addRotationKeys(Transaction txn,
+			ContactId c, SecretKey rootKey, long timestamp, boolean alice,
+			boolean active) throws DbException {
 		Map<TransportId, KeySetId> ids = new HashMap<>();
 		for (Entry<TransportId, TransportKeyManager> e : managers.entrySet()) {
 			TransportId t = e.getKey();
@@ -114,6 +114,14 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 		return ids;
 	}
 
+	@Override
+	public Map<TransportId, KeySetId> addRotationKeys(ContactId c,
+			SecretKey rootKey, long timestamp, boolean alice, boolean active)
+			throws DbException {
+		return db.transactionWithResult(false, txn ->
+				addRotationKeys(txn, c, rootKey, timestamp, alice, active));
+	}
+
 	@Override
 	public Map<TransportId, KeySetId> addContact(Transaction txn, ContactId c,
 			PublicKey theirPublicKey, KeyPair ourKeyPair)
@@ -137,7 +145,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			PendingContactId p, PublicKey theirPublicKey, KeyPair ourKeyPair)
 			throws DbException, GeneralSecurityException {
 		SecretKey staticMasterKey = transportCrypto
-					.deriveStaticMasterKey(theirPublicKey, ourKeyPair);
+				.deriveStaticMasterKey(theirPublicKey, ourKeyPair);
 		SecretKey rootKey =
 				transportCrypto.deriveHandshakeRootKey(staticMasterKey, true);
 		boolean alice = transportCrypto.isAlice(theirPublicKey, ourKeyPair);

bramble-core/src/test/java/org/briarproject/bramble/client/BdfMessageValidatorTest.java

@@ -13,7 +13,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.test.ValidatorTestCase;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOCK_DIFFERENCE;
@@ -38,7 +38,7 @@ public class BdfMessageValidatorTest extends ValidatorTestCase {
 	private final Metadata meta = new Metadata();
 
 	public BdfMessageValidatorTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 	}
 
 	@Test(expected = InvalidMessageException.class)

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

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

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

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

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

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

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

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

bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocolTest.java

@@ -11,8 +11,8 @@ import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.jmock.Expectations;
 import org.jmock.auto.Mock;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.jmock.integration.junit4.JUnitRuleMockery;
-import org.jmock.lib.legacy.ClassImposteriser;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -34,7 +34,7 @@ public class KeyAgreementProtocolTest extends BrambleTestCase {
 	@Rule
 	public JUnitRuleMockery context = new JUnitRuleMockery() {{
 		// So we can mock concrete classes like KeyAgreementTransport
-		setImposteriser(ClassImposteriser.INSTANCE);
+		setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 	}};
 
 	private final PublicKey alicePubKey = getAgreementPublicKey();

bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementTransportTest.java

@@ -14,7 +14,7 @@ import org.briarproject.bramble.api.record.RecordWriterFactory;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.CaptureArgumentAction;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import java.io.InputStream;
@@ -58,7 +58,7 @@ public class KeyAgreementTransportTest extends BrambleMockTestCase {
 	private KeyAgreementTransport kat;
 
 	public KeyAgreementTransportTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		inputStream = context.mock(InputStream.class);
 		outputStream = context.mock(OutputStream.class);
 	}

bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java

@@ -25,7 +25,7 @@ import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.briarproject.bramble.test.RunAction;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -69,7 +69,7 @@ public class PollerImplTest extends BrambleMockTestCase {
 	private PollerImpl poller;
 
 	public PollerImplTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		random = context.mock(SecureRandom.class);
 	}
 

bramble-core/witness.gradle

@@ -1,6 +1,7 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
+        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
+        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
         'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
@@ -19,11 +20,12 @@ dependencyVerification {
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
+        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
         'net.i2p.crypto:eddsa:0.2.0:eddsa-0.2.0.jar:a7cb1b85c16e2f0730b9204106929a1d9aaae1df728adc7041a8b8b605692140',
+        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
+        'net.jodah:concurrentunit:0.4.2:concurrentunit-0.4.2.jar:5583078e1acf91734939e985bc9e7ee947b0e93a8eef679da6bb07bbeb47ced3',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
-        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
-        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
-        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
+        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
         'org.bitlet:weupnp:0.1.4:weupnp-0.1.4.jar:88df7e6504929d00bdb832863761385c68ab92af945b04f0770b126270a444fb',
         'org.briarproject:jtorctl:0.3:jtorctl-0.3.jar:f2939238a097898998432effe93b0334d97a787972ab3a91a8973a1d309fc864',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
@@ -32,16 +34,18 @@ dependencyVerification {
         'org.codehaus.mojo:animal-sniffer-annotations:1.17:animal-sniffer-annotations-1.17.jar:92654f493ecfec52082e76354f0ebf87648dc3d5cec2e3c3cdb947c016747a53',
         'org.codehaus.mojo:animal-sniffer-ant-tasks:1.16:animal-sniffer-ant-tasks-1.16.jar:890040976fbe2d584619a6a61b1fd2e925b3b5eb342a85eb2762c467c0d64e90',
         'org.codehaus.mojo:animal-sniffer:1.16:animal-sniffer-1.16.jar:72be8bcc226ba43b937c722a08a07852bfa1b11400089265d5df0ee7b38b1d52',
-        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
-        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
+        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
+        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
+        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
         'org.hsqldb:hsqldb:2.3.5:hsqldb-2.3.5.jar:6676a6977ac98997a80f827ddbd3fe8ca1e0853dad1492512135fd1a222ccfad',
-        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
-        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
-        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
-        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
-        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
+        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
+        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
+        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
+        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
+        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
+        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
         'org.ow2.asm:asm-all:5.2:asm-all-5.2.jar:7fbffbc1db3422e2101689fd88df8384b15817b52b9b2b267b9f6d2511dc198d',
-        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
+        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
         'org.whispersystems:curve25519-java:0.5.0:curve25519-java-0.5.0.jar:0aadd43cf01d11e9b58f867b3c4f25c3194e8b0623d1953d32dfbfbee009e38d',
     ]
 }

bramble-java/build.gradle

@@ -23,10 +23,9 @@ dependencies {
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation project(path: ':bramble-core', configuration: 'testOutput')
-	testImplementation 'junit:junit:4.12'
-	testImplementation "org.jmock:jmock:2.8.2"
-	testImplementation "org.jmock:jmock-junit4:2.8.2"
-	testImplementation "org.jmock:jmock-legacy:2.8.2"
+	testImplementation "junit:junit:$junit_version"
+	testImplementation "org.jmock:jmock:$jmock_version"
+	testImplementation "org.jmock:jmock-junit4:$jmock_version"
 
 	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 }

bramble-java/witness.gradle

@@ -1,6 +1,7 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
+        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
+        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
         'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
@@ -17,24 +18,26 @@ dependencyVerification {
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
+        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
         'net.java.dev.jna:jna-platform:4.5.2:jna-platform-4.5.2.jar:f1d00c167d8921c6e23c626ef9f1c3ae0be473c95c68ffa012bc7ae55a87e2d6',
         'net.java.dev.jna:jna:4.5.2:jna-4.5.2.jar:0c8eb7acf67261656d79005191debaba3b6bf5dd60a43735a245429381dbecff',
+        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
-        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
-        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
-        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
+        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
         'org.briarproject:obfs4proxy:0.0.12-dev-40245c4a:obfs4proxy-0.0.12-dev-40245c4a.zip:172029e7058b3a83ac93ac4991a44bf76e16ce8d46f558f5836d57da3cb3a766',
         'org.briarproject:tor:0.3.5.13-1:tor-0.3.5.13-1.zip:ef35c16bf8dc1f4c75ed71d9f55e4514f383d124ec96b859aca647c990927c99',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
         'org.codehaus.mojo:animal-sniffer-annotations:1.17:animal-sniffer-annotations-1.17.jar:92654f493ecfec52082e76354f0ebf87648dc3d5cec2e3c3cdb947c016747a53',
-        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
-        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
-        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
-        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
-        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
-        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
-        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
-        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
+        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
+        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
+        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
+        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
+        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
+        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
+        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
+        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
+        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
+        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
     ]
 }

briar-android/build.gradle

@@ -28,7 +28,7 @@ android {
 		targetSdkVersion 29
 		versionCode 10218
 		versionName "1.2.18"
-		applicationId "org.briarproject.briar.android"
+		applicationId "org.briarproject.briar.socialbackup"
 
 		vectorDrawables.useSupportLibrary = true
 		buildConfigField "String", "GitHash",
@@ -106,6 +106,7 @@ dependencies {
 	implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
 	implementation 'com.google.android.material:material:1.2.1'
 	implementation 'androidx.recyclerview:recyclerview-selection:1.1.0-rc03'
+	implementation 'org.magmacollective.darkcrystal:dark-crystal-secret-sharing-wrapper:1.1.0'
 
 	implementation 'info.guardianproject.panic:panic:1.0'
 	implementation 'info.guardianproject.trustedintents:trustedintents:0.2'
@@ -136,11 +137,12 @@ dependencies {
 	testImplementation "androidx.arch.core:core-testing:2.1.0"
 	testImplementation "androidx.test.espresso:espresso-core:$espressoVersion"
 	testImplementation 'org.robolectric:robolectric:4.3.1'
-	testImplementation 'org.mockito:mockito-core:3.1.0'
-	testImplementation 'junit:junit:4.13.1'
-	testImplementation "org.jmock:jmock:$jmockVersion"
-	testImplementation "org.jmock:jmock-junit4:$jmockVersion"
-	testImplementation "org.jmock:jmock-legacy:$jmockVersion"
+
+	testImplementation 'org.mockito:mockito-core:3.9.0'
+	testImplementation "junit:junit:$junit_version"
+	testImplementation "org.jmock:jmock:$jmock_version"
+	testImplementation "org.jmock:jmock-junit4:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 	testAnnotationProcessor "com.google.dagger:dagger-compiler:2.24"
 
 	androidTestImplementation project(path: ':bramble-api', configuration: 'testOutput')

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_package" translatable="false">org.briarproject.briar.android.debug</string>
+	<string name="app_name" translatable="false">Briar SB Debug</string>
+	<string name="app_package" translatable="false">org.briarproject.briar.socialbackup.debug</string>
 </resources>

briar-android/src/main/AndroidManifest.xml

@@ -138,6 +138,43 @@
 			</intent-filter>
 		</activity>
 
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.SocialBackupSetupActivity"
+			android:label="@string/activity_name_distributed_backup"
+			android:parentActivityName="org.briarproject.briar.android.settings.SettingsActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.settings.SettingsActivity" />
+		</activity>
+
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardActivity"
+			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.socialbackup.recover.OwnerReturnShardActivity"
+			android:label="@string/activity_name_recovery"
+
+			android:parentActivityName="org.briarproject.briar.android.account.SetupActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.account.SetupActivity" />
+		</activity>
+
+		<activity
+			android:name="org.briarproject.briar.android.socialbackup.recover.RestoreAccountActivity"
+			android:label="@string/activity_name_restore_account"
+			android:parentActivityName="org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardActivity">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardActivity" />
+		</activity>
+
 		<activity
 			android:name="org.briarproject.briar.android.conversation.ConversationActivity"
 			android:label="@string/app_name"

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

@@ -8,11 +8,13 @@ import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.account.BriarAccountModule;
 import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.account.AccountManager;
+import org.briarproject.bramble.api.client.ClientHelper;
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
 import org.briarproject.bramble.api.crypto.PasswordStrengthEstimator;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.EventBus;
@@ -59,6 +61,7 @@ import org.briarproject.briar.api.privategroup.PrivateGroupFactory;
 import org.briarproject.briar.api.privategroup.PrivateGroupManager;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationFactory;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 import org.briarproject.briar.api.test.TestDataCreator;
 
 import java.util.concurrent.Executor;
@@ -184,6 +187,12 @@ public interface AndroidComponent
 
 	Thread.UncaughtExceptionHandler exceptionHandler();
 
+	SocialBackupManager socialBackupManager();
+
+    DatabaseComponent databaseComponent();
+
+    ClientHelper clientHelper();
+
 	void inject(SignInReminderReceiver briarService);
 
 	void inject(BriarService briarService);

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

@@ -42,6 +42,9 @@ import org.briarproject.briar.android.privategroup.list.GroupListModule;
 import org.briarproject.briar.android.reporting.DevReportModule;
 import org.briarproject.briar.android.settings.SettingsModule;
 import org.briarproject.briar.android.sharing.SharingModule;
+import org.briarproject.briar.android.socialbackup.SocialBackupSetupModule;
+import org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardModule;
+import org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardModule;
 import org.briarproject.briar.android.test.TestAvatarCreatorImpl;
 import org.briarproject.briar.android.viewmodel.ViewModelModule;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
@@ -49,6 +52,7 @@ 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;
@@ -83,12 +87,16 @@ import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 		SettingsModule.class,
 		DevReportModule.class,
 		ContactListModule.class,
+		AndroidDarkCrystalModule.class,
 		IntroductionModule.class,
 		// below need to be within same scope as ViewModelProvider.Factory
 		ForumModule.class,
 		GroupListModule.class,
 		GroupConversationModule.class,
 		SharingModule.class,
+		OwnerReturnShardModule.class,
+		CustodianReturnShardModule.class,
+		SocialBackupSetupModule.class
 })
 public class AppModule {
 

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

@@ -30,6 +30,7 @@ public class AuthorNameFragment extends SetupFragment {
 	private TextInputLayout authorNameWrapper;
 	private TextInputEditText authorNameInput;
 	private Button nextButton;
+	private Button recoverButton;
 
 	public static AuthorNameFragment newInstance() {
 		return new AuthorNameFragment();
@@ -54,6 +55,9 @@ public class AuthorNameFragment extends SetupFragment {
 		authorNameInput.addTextChangedListener(this);
 		nextButton.setOnClickListener(this);
 
+		recoverButton = v.findViewById(R.id.buttonRestoreAccount);
+		recoverButton.setOnClickListener(e -> viewModel.recoverClicked());
+
 		return v;
 	}
 
@@ -75,6 +79,8 @@ public class AuthorNameFragment extends SetupFragment {
 		boolean enabled = authorNameLength > 0 && !error;
 		authorNameInput.setOnEditorActionListener(enabled ? this : null);
 		nextButton.setEnabled(enabled);
+		recoverButton.setEnabled(!enabled);
+//		recoverButton.setVisibility(enabled ? View.INVISIBLE : View.VISIBLE);
 	}
 
 	@Override

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

@@ -2,7 +2,7 @@ package org.briarproject.briar.android.account;
 
 import android.content.Context;
 
-interface DozeHelper {
+public interface DozeHelper {
 
 	boolean needToShowDozeFragment(Context context);
 }

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

@@ -14,7 +14,7 @@ import static org.briarproject.briar.android.util.UiUtils.needsDozeWhitelisting;
 
 @UiThread
 @NotNullByDefault
-class DozeView extends PowerView {
+public class DozeView extends PowerView {
 
 	@Nullable
 	private Runnable onButtonClickListener;

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

@@ -21,7 +21,7 @@ import static android.os.Build.VERSION.SDK_INT;
 
 @UiThread
 @NotNullByDefault
-class HuaweiView extends PowerView {
+public class HuaweiView extends PowerView {
 
 	private final static String PACKAGE_NAME = "com.huawei.systemmanager";
 	private final static String CLASS_NAME =

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

@@ -24,7 +24,7 @@ import static org.briarproject.briar.android.util.UiUtils.showOnboardingDialog;
 
 @UiThread
 @NotNullByDefault
-abstract class PowerView extends ConstraintLayout {
+public abstract class PowerView extends ConstraintLayout {
 
 	private final TextView textView;
 	private final ImageView checkImage;
@@ -156,7 +156,7 @@ abstract class PowerView extends ConstraintLayout {
 		};
 	}
 
-	interface OnCheckedChangedListener {
+	public interface OnCheckedChangedListener {
 		void onCheckedChanged();
 	}
 

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/account/SetupActivity.java

@@ -10,6 +10,7 @@ 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.BaseFragmentListener;
+import org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardActivity;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
@@ -25,6 +26,7 @@ import static org.briarproject.briar.android.account.SetupViewModel.State.AUTHOR
 import static org.briarproject.briar.android.account.SetupViewModel.State.CREATED;
 import static org.briarproject.briar.android.account.SetupViewModel.State.DOZE;
 import static org.briarproject.briar.android.account.SetupViewModel.State.FAILED;
+import static org.briarproject.briar.android.account.SetupViewModel.State.RECOVER;
 import static org.briarproject.briar.android.account.SetupViewModel.State.SET_PASSWORD;
 
 @MethodsNotNullByDefault
@@ -60,6 +62,8 @@ public class SetupActivity extends BaseActivity
 			showPasswordFragment();
 		} else if (state == DOZE) {
 			showDozeFragment();
+		} else if (state == RECOVER) {
+			recover();
 		} else if (state == CREATED || state == FAILED) {
 			// TODO: Show an error if failed
 			showApp();
@@ -84,6 +88,13 @@ public class SetupActivity extends BaseActivity
 		overridePendingTransition(R.anim.screen_new_in, R.anim.screen_old_out);
 	}
 
+	void recover () {
+//		finish();
+		Intent i = new Intent(this, OwnerReturnShardActivity.class);
+		i.addFlags(FLAG_ACTIVITY_NEW_TASK);
+		startActivity(i);
+	}
+
 	@Override
 	@Deprecated
 	public void runOnDbThread(Runnable runnable) {

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

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

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

@@ -25,12 +25,14 @@ import static org.briarproject.briar.android.account.SetupViewModel.State.AUTHOR
 import static org.briarproject.briar.android.account.SetupViewModel.State.CREATED;
 import static org.briarproject.briar.android.account.SetupViewModel.State.DOZE;
 import static org.briarproject.briar.android.account.SetupViewModel.State.FAILED;
+import static org.briarproject.briar.android.account.SetupViewModel.State.RECOVER;
 import static org.briarproject.briar.android.account.SetupViewModel.State.SET_PASSWORD;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
+public
 class SetupViewModel extends AndroidViewModel {
-	enum State {AUTHOR_NAME, SET_PASSWORD, DOZE, CREATED, FAILED}
+	enum State {AUTHOR_NAME, SET_PASSWORD, DOZE, CREATED, FAILED, RECOVER}
 
 	private static final Logger LOG =
 			getLogger(SetupActivity.class.getName());
@@ -116,4 +118,9 @@ class SetupViewModel extends AndroidViewModel {
 			}
 		});
 	}
+
+	public void recoverClicked() {
+		LOG.info("RECOVER CLICKED ***");
+	  state.postEvent(RECOVER);
+	}
 }

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

@@ -2,6 +2,7 @@ package org.briarproject.briar.android.activity;
 
 import android.app.Activity;
 
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.briar.android.AndroidComponent;
 import org.briarproject.briar.android.StartupFailureActivity;
 import org.briarproject.briar.android.account.AuthorNameFragment;
@@ -77,20 +78,40 @@ import org.briarproject.briar.android.sharing.ShareBlogFragment;
 import org.briarproject.briar.android.sharing.ShareForumActivity;
 import org.briarproject.briar.android.sharing.ShareForumFragment;
 import org.briarproject.briar.android.sharing.SharingModule;
+import org.briarproject.briar.android.socialbackup.SetupExplainerFragment;
+import org.briarproject.briar.android.socialbackup.recover.CustodianRecoveryModeExplainerFragment;
+import org.briarproject.briar.android.socialbackup.CustodianSelectorFragment;
+import org.briarproject.briar.android.socialbackup.SocialBackupSetupActivity;
+import org.briarproject.briar.android.socialbackup.ExistingBackupFragment;
+import org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardActivity;
+import org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardErrorFragment;
+import org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardFragment;
+import org.briarproject.briar.android.socialbackup.recover.OwnerRecoveryModeErrorFragment;
+import org.briarproject.briar.android.socialbackup.recover.OwnerRecoveryModeExplainerFragment;
+import org.briarproject.briar.android.socialbackup.recover.OwnerRecoveryModeMainFragment;
+import org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardActivity;
+import org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardFragment;
+import org.briarproject.briar.android.socialbackup.ThresholdSelectorFragment;
+import org.briarproject.briar.android.socialbackup.creation.CreateBackupModule;
+import org.briarproject.briar.android.socialbackup.recover.OwnerReturnShardSuccessFragment;
+import org.briarproject.briar.android.socialbackup.recover.RestoreAccountActivity;
+import org.briarproject.briar.android.socialbackup.recover.RestoreAccountDozeFragment;
+import org.briarproject.briar.android.socialbackup.recover.RestoreAccountSetPasswordFragment;
 import org.briarproject.briar.android.splash.SplashScreenActivity;
 import org.briarproject.briar.android.test.TestDataActivity;
 
 import dagger.Component;
 
 @ActivityScope
-@Component(modules = {
+@Component(modules ={
 		ActivityModule.class,
 		BlogModule.class,
 		CreateGroupModule.class,
 		GroupInvitationModule.class,
 		GroupMemberModule.class,
 		GroupRevealModule.class,
-		SharingModule.SharingLegacyModule.class
+		SharingModule.SharingLegacyModule.class,
+		CreateBackupModule.class
 }, dependencies = AndroidComponent.class)
 public interface ActivityComponent {
 
@@ -180,6 +201,14 @@ public interface ActivityComponent {
 
 	void inject(CrashReportActivity crashReportActivity);
 
+	void inject(CustodianReturnShardActivity custodianReturnShardActivity);
+
+    void inject(OwnerReturnShardActivity ownerReturnShardActivity);
+
+    void inject(OwnerRecoveryModeMainFragment ownerRecoveryModeMainFragment);
+
+    void inject(RestoreAccountActivity restoreAccountActivity);
+
 	// Fragments
 
 	void inject(AuthorNameFragment fragment);
@@ -238,4 +267,33 @@ public interface ActivityComponent {
 
 	void inject(ConfirmAvatarDialogFragment fragment);
 
+	void inject(ThresholdSelectorFragment thresholdSelectorFragment);
+
+	void inject(SocialBackupSetupActivity distributedBackupActivity);
+
+	void inject(DatabaseComponent databaseComponent);
+
+	void inject(CustodianSelectorFragment custodianSelectorFragment);
+
+	void inject(OwnerRecoveryModeExplainerFragment ownerRecoveryModeExplainerFragment);
+
+	void inject(ExistingBackupFragment existingBackupFragment);
+
+	void inject(CustodianRecoveryModeExplainerFragment custodianRecoveryModeExplainerFragment);
+
+	void inject(CustodianReturnShardFragment custodianReturnShardFragment);
+
+	void inject(OwnerReturnShardFragment ownerReturnShardFragment);
+
+	void inject(RestoreAccountSetPasswordFragment restoreAccountSetPasswordFragment);
+
+	void inject(RestoreAccountDozeFragment restoreAccountDozeFragment);
+
+	void inject(OwnerReturnShardSuccessFragment ownerReturnShardSuccessFragment);
+
+	void inject(OwnerRecoveryModeErrorFragment ownerRecoveryModeErrorFragment);
+
+	void inject(CustodianReturnShardErrorFragment custodianReturnShardErrorFragment);
+
+	void inject(SetupExplainerFragment setupExplainerFragment);
 }

briar-android/src/main/java/org/briarproject/briar/android/contact/add/nearby/AddNearbyContactFragment.java

@@ -45,7 +45,7 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 public class AddNearbyContactFragment extends BaseFragment
 		implements QrCodeView.FullscreenListener {
 
-	static final String TAG = AddNearbyContactFragment.class.getName();
+	public static final String TAG = AddNearbyContactFragment.class.getName();
 
 	private static final Logger LOG = Logger.getLogger(TAG);
 

briar-android/src/main/java/org/briarproject/briar/android/contact/add/nearby/AddNearbyContactPermissionManager.java

@@ -25,7 +25,7 @@ import static androidx.core.app.ActivityCompat.shouldShowRequestPermissionRation
 import static androidx.core.content.ContextCompat.checkSelfPermission;
 import static org.briarproject.briar.android.util.UiUtils.getGoToSettingsListener;
 
-class AddNearbyContactPermissionManager {
+public class AddNearbyContactPermissionManager {
 
 	private enum Permission {
 		UNKNOWN, GRANTED, SHOW_RATIONALE, PERMANENTLY_DENIED
@@ -38,7 +38,7 @@ class AddNearbyContactPermissionManager {
 	private final Consumer<String[]> requestPermissions;
 	private final boolean isBluetoothSupported;
 
-	AddNearbyContactPermissionManager(FragmentActivity ctx,
+	public AddNearbyContactPermissionManager(FragmentActivity ctx,
 			Consumer<String[]> requestPermissions,
 			boolean isBluetoothSupported) {
 		this.ctx = ctx;
@@ -46,7 +46,7 @@ class AddNearbyContactPermissionManager {
 		this.isBluetoothSupported = isBluetoothSupported;
 	}
 
-	void resetPermissions() {
+	public void resetPermissions() {
 		cameraPermission = Permission.UNKNOWN;
 		locationPermission = Permission.UNKNOWN;
 	}
@@ -64,7 +64,7 @@ class AddNearbyContactPermissionManager {
 		}
 	}
 
-	static boolean areEssentialPermissionsGranted(Context ctx,
+	public static boolean areEssentialPermissionsGranted(Context ctx,
 			boolean isBluetoothSupported) {
 		int ok = PERMISSION_GRANTED;
 		return checkSelfPermission(ctx, CAMERA) == ok &&
@@ -79,7 +79,7 @@ class AddNearbyContactPermissionManager {
 						!isBluetoothSupported);
 	}
 
-	boolean checkPermissions() {
+	public boolean checkPermissions() {
 		boolean locationEnabled = isLocationEnabled(ctx);
 		if (locationEnabled && areEssentialPermissionsGranted()) return true;
 		// If an essential permission has been permanently denied, ask the
@@ -164,7 +164,7 @@ class AddNearbyContactPermissionManager {
 		requestPermissions.accept(permissions);
 	}
 
-	void onRequestPermissionResult(Map<String, Boolean> result,
+	public void onRequestPermissionResult(Map<String, Boolean> result,
 			Runnable onPermissionsGranted) {
 		if (gotPermission(CAMERA, result)) {
 			cameraPermission = Permission.GRANTED;

briar-android/src/main/java/org/briarproject/briar/android/contact/add/nearby/CameraException.java

@@ -2,7 +2,7 @@ package org.briarproject.briar.android.contact.add.nearby;
 
 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/contact/add/nearby/QrCodeDecoder.java

@@ -32,7 +32,7 @@ import static java.util.logging.Logger.getLogger;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
+public class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 
 	private static final Logger LOG = getLogger(QrCodeDecoder.class.getName());
 
@@ -44,7 +44,7 @@ class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	private Camera camera = null;
 	private int cameraIndex = 0;
 
-	QrCodeDecoder(AndroidExecutor androidExecutor,
+	public QrCodeDecoder(AndroidExecutor androidExecutor,
 			@IoExecutor Executor ioExecutor, ResultCallback callback) {
 		this.androidExecutor = androidExecutor;
 		this.ioExecutor = ioExecutor;
@@ -127,7 +127,7 @@ class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	}
 
 	@NotNullByDefault
-	interface ResultCallback {
+	public interface ResultCallback {
 		@IoExecutor
 		void onQrCodeDecoded(Result result);
 	}

briar-android/src/main/java/org/briarproject/briar/android/contact/add/nearby/QrCodeUtils.java

@@ -22,12 +22,12 @@ import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
-class QrCodeUtils {
+public class QrCodeUtils {
 
 	private static final Logger LOG = 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/contactselection/BaseContactSelectorFragment.java

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

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

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

briar-android/src/main/java/org/briarproject/briar/android/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.recover.CustodianReturnShardActivity;
 import org.briarproject.briar.android.util.BriarSnackbarBuilder;
 import org.briarproject.briar.android.view.BriarRecyclerView;
 import org.briarproject.briar.android.view.ImagePreview;
@@ -370,6 +371,13 @@ public class ConversationActivity extends BriarActivity
 		observeOnce(viewModel.getContactItem(), this, contact ->
 				menu.findItem(R.id.action_set_alias).setEnabled(true));
 
+		// enable help recover account action if available
+		observeOnce(viewModel.amCustodian(), this, enable -> {
+			if (enable) {
+				menu.findItem(R.id.action_help_recover_account).setEnabled(true);
+			}
+		});
+
 		return super.onCreateOptionsMenu(menu);
 	}
 
@@ -396,6 +404,12 @@ 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, CustodianReturnShardActivity.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/ConversationViewModel.java

@@ -40,6 +40,8 @@ import org.briarproject.briar.api.messaging.PrivateMessage;
 import org.briarproject.briar.api.messaging.PrivateMessageFactory;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.messaging.event.AttachmentReceivedEvent;
+import org.briarproject.briar.api.socialbackup.SocialBackup;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 
 import java.util.Collection;
 import java.util.List;
@@ -84,6 +86,7 @@ public class ConversationViewModel extends DbViewModel
 	private final PrivateMessageFactory privateMessageFactory;
 	private final AttachmentRetriever attachmentRetriever;
 	private final AttachmentCreator attachmentCreator;
+	private final SocialBackupManager socialBackupManager;
 
 	@Nullable
 	private ContactId contactId = null;
@@ -104,6 +107,7 @@ public class ConversationViewModel extends DbViewModel
 			new MutableLiveData<>();
 	private final MutableLiveEvent<PrivateMessageHeader> addedHeader =
 			new MutableLiveEvent<>();
+    private final MutableLiveData<Boolean> amCustodian = new MutableLiveData<>();
 
 	@Inject
 	ConversationViewModel(Application application,
@@ -118,7 +122,8 @@ public class ConversationViewModel extends DbViewModel
 			SettingsManager settingsManager,
 			PrivateMessageFactory privateMessageFactory,
 			AttachmentRetriever attachmentRetriever,
-			AttachmentCreator attachmentCreator) {
+			AttachmentCreator attachmentCreator,
+			SocialBackupManager socialBackupManager) {
 		super(application, dbExecutor, lifecycleManager, db, androidExecutor);
 		this.db = db;
 		this.eventBus = eventBus;
@@ -129,6 +134,7 @@ public class ConversationViewModel extends DbViewModel
 		this.privateMessageFactory = privateMessageFactory;
 		this.attachmentRetriever = attachmentRetriever;
 		this.attachmentCreator = attachmentCreator;
+		this.socialBackupManager = socialBackupManager;
 		messagingGroupId = map(contactItem, c ->
 				messagingManager.getContactGroup(c.getContact()).getId());
 		contactDeleted.setValue(false);
@@ -296,6 +302,12 @@ public class ConversationViewModel extends DbViewModel
 			onOnboardingShown(SHOW_ONBOARDING_INTRODUCTION);
 			showIntroductionOnboarding.postEvent(true);
 		}
+
+		// Check if we are a social backup custodian for this contact
+		boolean amCustodianBool = db.transactionWithResult(true,
+				txn -> socialBackupManager.amCustodian(txn, c));
+		amCustodian.postValue(amCustodianBool);
+
 	}
 
 	@DatabaseExecutor
@@ -381,6 +393,10 @@ public class ConversationViewModel extends DbViewModel
 		return addedHeader;
 	}
 
+	LiveData<Boolean> amCustodian() {
+		return amCustodian;
+	}
+
 	@UiThread
 	void recheckFeaturesAndOnboarding(ContactId contactId) {
 		runOnDbThread(() -> {

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 +293,21 @@ class ConversationVisitor implements
 		}
 	}
 
+	@Override
+	public ConversationItem visitShardMessage(ShardMessageHeader r) {
+		if (r.isLocal()) {
+			String text = ctx.getString(R.string.social_backup_shard_sent,
+					contactName.getValue());
+			return new ConversationNoticeItem(
+					R.layout.list_item_conversation_notice_out, text, r);
+		} else {
+			String text = ctx.getString(R.string.social_backup_shard_received,
+					contactName.getValue());
+			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/navdrawer/NavDrawerActivity.java

@@ -158,7 +158,8 @@ public class NavDrawerActivity extends BriarActivity implements
 			@Override
 			public void onDrawerOpened(View drawerView) {
 				super.onDrawerOpened(drawerView);
-				navDrawerViewModel.checkTransportsOnboarding();
+//				navDrawerViewModel.checkTransportsOnboarding();
+				navDrawerViewModel.checkSocialBackupOnboarding();
 			}
 		};
 		drawerLayout.addDrawerListener(drawerToggle);
@@ -167,9 +168,12 @@ public class NavDrawerActivity extends BriarActivity implements
 		initializeTransports();
 		transportsView.setAdapter(transportsAdapter);
 
-		observeOnce(navDrawerViewModel.showTransportsOnboarding(), this, show ->
-				observeOnce(torIcon, this, imageView ->
-						showTransportsOnboarding(show, imageView)));
+//		observeOnce(navDrawerViewModel.showTransportsOnboarding(), this, show ->
+//				observeOnce(torIcon, this, imageView ->
+//						showTransportsOnboarding(show, imageView)));
+
+		observeOnce(navDrawerViewModel.showSocialBackupOnboarding(), this,
+				this::showSocialBackupOnboarding);
 
 		lockManager.isLockable().observe(this, this::setLockVisible);
 
@@ -468,6 +472,22 @@ public class NavDrawerActivity extends BriarActivity implements
 		}
 	}
 
+	private void showSocialBackupOnboarding(boolean show) {
+		if (show) {
+			new MaterialTapTargetPrompt.Builder(NavDrawerActivity.this,
+					R.style.OnboardingDialogTheme)
+					.setTarget(R.id.nav_btn_settings)
+					.setPrimaryText(R.string.social_backup_onboarding_title)
+					.setSecondaryText(R.string.social_backup_onboarding_long)
+					.setFocalRadius((float) 350)
+					.setFocalPadding((float) 100)
+					.setBackgroundColour(
+							ContextCompat.getColor(this, R.color.briar_primary))
+					.show();
+			navDrawerViewModel.socialBackupOnboardingShown();
+		}
+	}
+
 	private static class Transport {
 
 		private final TransportId id;

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerViewModel.java

@@ -39,6 +39,8 @@ public class NavDrawerViewModel extends DbViewModel {
 	private static final String EXPIRY_DATE_WARNING = "expiryDateWarning";
 	private static final String SHOW_TRANSPORTS_ONBOARDING =
 			"showTransportsOnboarding";
+	private static final String SHOW_SOCIAL_BACKUP_ONBOARDING =
+			"showSocialBackupOnboarding";
 
 	private final SettingsManager settingsManager;
 
@@ -48,6 +50,8 @@ public class NavDrawerViewModel extends DbViewModel {
 			new MutableLiveData<>();
 	private final MutableLiveData<Boolean> showTransportsOnboarding =
 			new MutableLiveData<>();
+	private final MutableLiveData<Boolean> showSocialBackupOnboarding =
+			new MutableLiveData<>();
 
 	@Inject
 	NavDrawerViewModel(Application app,
@@ -142,6 +146,11 @@ public class NavDrawerViewModel extends DbViewModel {
 		return showTransportsOnboarding;
 	}
 
+	@UiThread
+	LiveData<Boolean> showSocialBackupOnboarding() {
+		return showSocialBackupOnboarding;
+	}
+
 	@UiThread
 	void checkTransportsOnboarding() {
 		if (showTransportsOnboarding.getValue() != null) return;
@@ -171,4 +180,35 @@ public class NavDrawerViewModel extends DbViewModel {
 			}
 		});
 	}
+
+	@UiThread
+	void checkSocialBackupOnboarding() {
+		if (showSocialBackupOnboarding.getValue() != null) return;
+		runOnDbThread(() -> {
+			try {
+				Settings settings =
+						settingsManager.getSettings(SETTINGS_NAMESPACE);
+				boolean show =
+						settings.getBoolean(SHOW_SOCIAL_BACKUP_ONBOARDING,
+								true);
+				showSocialBackupOnboarding.postValue(show);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
+	@UiThread
+	void socialBackupOnboardingShown() {
+		showSocialBackupOnboarding.setValue(false);
+		runOnDbThread(() -> {
+			try {
+				Settings settings = new Settings();
+				settings.putBoolean(SHOW_SOCIAL_BACKUP_ONBOARDING, false);
+				settingsManager.mergeSettings(settings, SETTINGS_NAMESPACE);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
 }

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsActivity.java

@@ -1,10 +1,12 @@
 package org.briarproject.briar.android.settings;
 
 import android.content.Intent;
+import android.graphics.drawable.Drawable;
 import android.net.Uri;
 import android.os.Bundle;
 import android.view.MenuItem;
 import android.view.View;
+import android.widget.ImageView;
 import android.widget.TextView;
 import android.widget.Toast;
 
@@ -12,6 +14,7 @@ import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.navdrawer.NavDrawerActivity;
 import org.briarproject.briar.android.util.UiUtils;
 import org.briarproject.briar.android.view.AuthorView;
 
@@ -19,11 +22,15 @@ import javax.inject.Inject;
 
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.ActionBar;
+import androidx.core.content.ContextCompat;
 import androidx.lifecycle.ViewModelProvider;
+import androidx.vectordrawable.graphics.drawable.VectorDrawableCompat;
 import de.hdodenhof.circleimageview.CircleImageView;
+import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt;
 
 import static android.widget.Toast.LENGTH_LONG;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_AVATAR_IMAGE;
+import static org.briarproject.briar.android.util.UiUtils.resolveColorAttribute;
 
 public class SettingsActivity extends BriarActivity {
 

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

@@ -0,0 +1,105 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.view.MenuItem;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.socialbackup.creation.CreateBackupController;
+import org.briarproject.briar.android.contactselection.BaseContactSelectorAdapter;
+import org.briarproject.briar.android.contactselection.ContactSelectorController;
+import org.briarproject.briar.android.contactselection.ContactSelectorFragment;
+import org.briarproject.briar.android.contactselection.SelectableContactItem;
+import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;
+
+import java.util.Collection;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+
+import static java.util.Objects.requireNonNull;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class CustodianSelectorFragment extends ContactSelectorFragment {
+
+	public static final String TAG = CustodianSelectorFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private SocialBackupSetupViewModel viewModel;
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(SocialBackupSetupViewModel.class);
+	}
+
+	@Inject
+	CreateBackupController controller;
+
+	public static CustodianSelectorFragment newInstance() {
+		Bundle args = new Bundle();
+
+		CustodianSelectorFragment fragment = new CustodianSelectorFragment();
+		fragment.setArguments(args);
+
+		return fragment;
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+
+		requireActivity().setTitle(R.string.title_select_custodians);
+	}
+
+	@Override
+	protected ContactSelectorController<SelectableContactItem> getController() {
+		return controller;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	protected void onSelectionChanged() {
+		super.onSelectionChanged();
+		if (menu == null) return;
+		MenuItem item = menu.findItem(R.id.action_contacts_selected);
+		if (item == null) return;
+
+		BaseContactSelectorAdapter a = adapter;
+		selectedContacts = a.getSelectedContactIds();
+
+		int n = selectedContacts.size();
+		int min = 2;
+		int max = 7;
+		boolean amountIsValid = (n >= min) && (n <= max);
+
+		item.setVisible(amountIsValid);
+		if (n == 0) {
+			Toast.makeText(getContext(), String.format(getString(R.string.select_at_least_n_contacts), min),
+					Toast.LENGTH_SHORT).show();
+		} else if (n < min) {
+			Toast.makeText(getContext(), String.format(getString(R.string.select_at_least_n_more_contacts), min - n),
+					Toast.LENGTH_SHORT).show();
+		} else if (n > max) {
+			Toast.makeText(getContext(), String.format(getString(R.string.select_no_more_than_n_contacts), max),
+					Toast.LENGTH_SHORT).show();
+		}
+	}
+
+}

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

@@ -0,0 +1,57 @@
+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.DarkCrystal;
+import org.briarproject.briar.api.socialbackup.Shard;
+import org.magmacollective.darkcrystal.secretsharingwrapper.SecretSharingWrapper;
+
+import java.security.GeneralSecurityException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+
+import javax.inject.Inject;
+
+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) {
+		Random random = new Random();
+		byte[] secretId = new byte[SECRET_ID_BYTES];
+		random.nextBytes(secretId);
+		List<byte[]> shardsBytes = SecretSharingWrapper
+				.share(secret.getBytes(), numShards, threshold);
+		List<Shard> shards = new ArrayList<>(numShards);
+		for (byte[] shardBytes : shardsBytes) {
+			shards.add(new Shard(secretId, shardBytes));
+		}
+		return shards;
+	}
+
+	@Override
+	public SecretKey combineShards(List<Shard> shards) throws
+			GeneralSecurityException {
+		// Check each shard has the same secret Id
+		byte[] secretId = shards.get(0).getSecretId();
+		for (Shard shard : shards) {
+			if (!Arrays.equals(shard.getSecretId(), secretId))
+				throw new GeneralSecurityException();
+		}
+		List<byte[]> shardsBytes = new ArrayList<>(shards.size());
+		for (Shard shard : shards) {
+			shardsBytes.add(shard.getShard());
+		}
+		byte[] secretBytes = SecretSharingWrapper.combine(shardsBytes);
+		return new SecretKey(secretBytes);
+	}
+}

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

@@ -0,0 +1,125 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.text.Spannable;
+import android.text.SpannableStringBuilder;
+import android.text.style.ImageSpan;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.TextView;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.contact.ContactListAdapter;
+import org.briarproject.briar.android.contact.ContactListItem;
+import org.briarproject.briar.android.contact.OnContactClickListener;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.briarproject.briar.android.view.BriarRecyclerView;
+
+import java.util.Arrays;
+
+import javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+import androidx.recyclerview.widget.LinearLayoutManager;
+
+public class ExistingBackupFragment extends BaseFragment implements
+		OnContactClickListener<ContactListItem> {
+
+	public static final String TAG = ExistingBackupFragment.class.getName();
+	private final ContactListAdapter adapter = new ContactListAdapter(this);
+	private BriarRecyclerView list;
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private SocialBackupSetupViewModel viewModel;
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(SocialBackupSetupViewModel.class);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_distributed_backup);
+
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable
+			ViewGroup container, @Nullable Bundle savedInstanceState) {
+		// change toolbar text (relevant when navigating back to this fragment)
+//		requireActivity().setTitle(R.string.social_backup_trusted_contacts);
+
+		View view = inflater.inflate(R.layout.fragment_existing_backup,
+				container, false);
+		viewModel.loadCustodianList();
+		list = view.findViewById(R.id.custodianList);
+		list.setLayoutManager(new LinearLayoutManager(getActivity()));
+		list.setAdapter(adapter);
+		list.setEmptyText(R.string.no_contacts);
+
+		viewModel.getContactListItems().observe(getViewLifecycleOwner(),
+				result -> result.onError(this::handleException)
+						.onSuccess(adapter::submitList)
+		);
+
+		int threshold = viewModel.getThresholdFromExistingBackup();
+		int numberOfCustodians =
+				viewModel.getNumberOfCustodiansFromExistingBackup();
+
+		TextView mOfn = view.findViewById(R.id.textViewThreshold);
+		mOfn.setText(String.format(
+				getString(R.string.existing_backup_explain), threshold));
+
+		TextView thresholdRepresentation =
+				view.findViewById(R.id.textViewThresholdRepresentation);
+		thresholdRepresentation.setText(
+				buildThresholdRepresentationString(threshold,
+						numberOfCustodians));
+		return view;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void onItemClick(View view, ContactListItem item) {
+	}
+
+	private SpannableStringBuilder buildThresholdRepresentationString(
+			int threshold, int numberOfCustodians) {
+		char[] charArray = new char[numberOfCustodians];
+		Arrays.fill(charArray, ' ');
+		SpannableStringBuilder string =
+				new SpannableStringBuilder(new String(charArray));
+
+		for (int i = 0; i < numberOfCustodians; i++) {
+			int drawable = i < threshold
+					? R.drawable.ic_custodian_required
+					: R.drawable.ic_custodian_optional;
+			string.setSpan(new ImageSpan(getContext(), drawable), i,
+					i + 1,
+					Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
+		}
+		// If we have more than 6, split it on two lines
+		if (numberOfCustodians > 6) string.insert(4, "\n");
+		return string;
+	}
+}

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

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

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/SetupExplainerFragment.java

@@ -0,0 +1,54 @@
+package org.briarproject.briar.android.socialbackup;
+
+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 javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+
+public class SetupExplainerFragment extends BaseFragment {
+
+	public static final String TAG =
+			SetupExplainerFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private SocialBackupSetupViewModel viewModel;
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(SocialBackupSetupViewModel.class);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater, @Nullable
+			ViewGroup container, @Nullable Bundle savedInstanceState) {
+		View view =
+				inflater.inflate(R.layout.fragment_social_backup_setup_explainer,
+						container, false);
+
+		Button button = view.findViewById(R.id.button);
+		button.setOnClickListener(e -> viewModel.onExplainerDismissed());
+		return view;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+}
+

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

@@ -0,0 +1,94 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.os.Bundle;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.contactselection.ContactSelectorListener;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import java.util.Collection;
+import java.util.List;
+
+import javax.inject.Inject;
+
+import androidx.lifecycle.ViewModelProvider;
+
+public class SocialBackupSetupActivity extends BriarActivity implements
+		BaseFragment.BaseFragmentListener, ContactSelectorListener {
+
+	private SocialBackupSetupViewModel viewModel;
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(this, viewModelFactory)
+				.get(SocialBackupSetupViewModel.class);
+	}
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_distributed_backup);
+
+		if (viewModel.haveExistingBackup()) {
+			showInitialFragment(new ExistingBackupFragment());
+		} else {
+			try {
+				if (!viewModel.haveEnoughContacts()) {
+					Toast.makeText(this,
+							R.string.social_backup_not_enough_contacts,
+							Toast.LENGTH_LONG).show();
+					finish();
+				}
+			} catch (DbException dbException) {
+				Toast.makeText(this,
+						R.string.reading_contacts_error,
+						Toast.LENGTH_LONG).show();
+				finish();
+			}
+			showInitialFragment(new SetupExplainerFragment());
+		}
+
+		viewModel.getState()
+				.observe(this, this::onStateChanged);
+	}
+
+	private void onStateChanged(SocialBackupSetupViewModel.State state) {
+		switch (state) {
+			case SUCCESS:
+				finish();
+				break;
+			case FAILURE:
+				Toast.makeText(this,
+						"There was an error when creating the backup",
+						Toast.LENGTH_LONG).show();
+				finish();
+				break;
+			case CHOOSING_CUSTODIANS:
+				CustodianSelectorFragment fragment =
+						CustodianSelectorFragment.newInstance();
+				showNextFragment(fragment);
+				break;
+		}
+	}
+
+	@Override
+	public void contactsSelected(Collection<ContactId> contacts) {
+		Toast.makeText(this,
+				String.format("Selected %d contacts", contacts.size()),
+				Toast.LENGTH_SHORT).show();
+		viewModel.setCustodians((List<ContactId>) contacts);
+		ThresholdSelectorFragment fragment =
+				ThresholdSelectorFragment.newInstance(contacts.size());
+		showNextFragment(fragment);
+	}
+
+}

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

@@ -0,0 +1,20 @@
+package org.briarproject.briar.android.socialbackup;
+
+import org.briarproject.briar.android.socialbackup.recover.CustodianReturnShardViewModel;
+import org.briarproject.briar.android.viewmodel.ViewModelKey;
+
+import androidx.lifecycle.ViewModel;
+import dagger.Binds;
+import dagger.Module;
+import dagger.multibindings.IntoMap;
+
+@Module
+public abstract class SocialBackupSetupModule {
+
+	@Binds
+	@IntoMap
+	@ViewModelKey(SocialBackupSetupViewModel.class)
+	abstract ViewModel bindSocialBackupSetupViewModel(
+			SocialBackupSetupViewModel socialBackupSetupViewModel);
+
+}

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

@@ -0,0 +1,147 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.app.Application;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.briar.android.contact.ContactsViewModel;
+import org.briarproject.briar.api.conversation.ConversationManager;
+import org.briarproject.briar.api.identity.AuthorManager;
+import org.briarproject.briar.api.socialbackup.BackupMetadata;
+import org.briarproject.briar.api.socialbackup.SocialBackupManager;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.lifecycle.MutableLiveData;
+
+public class SocialBackupSetupViewModel extends ContactsViewModel {
+
+	private final SocialBackupManager socialBackupManager;
+	private final DatabaseComponent db;
+	private final ContactManager contactManager;
+	private BackupMetadata backupMetadata;
+	private List<ContactId> custodians;
+	private int threshold;
+
+
+	public enum State {
+		EXPLAINING,
+		CHOOSING_CUSTODIANS,
+		GETTING_THRESHOLD,
+		SUCCESS,
+		FAILURE
+	}
+
+	private final MutableLiveData<State> state =
+			new MutableLiveData<>();
+	@Inject
+	public SocialBackupSetupViewModel(
+			@NonNull Application app,
+			DatabaseComponent db,
+			@DatabaseExecutor Executor dbExecutor,
+			LifecycleManager lifecycleManager,
+			AuthorManager authorManager,
+			ConversationManager conversationManager,
+			ConnectionRegistry connectionRegistry,
+			EventBus eventBus,
+			AndroidExecutor androidExecutor,
+			SocialBackupManager socialBackupManager,
+			ContactManager contactManager
+	) {
+		super(app, dbExecutor, lifecycleManager, db, androidExecutor,
+				contactManager, authorManager, conversationManager,
+				connectionRegistry, eventBus);
+
+		this.socialBackupManager = socialBackupManager;
+		this.db = db;
+		this.contactManager = contactManager;
+	}
+
+    public void loadCustodianList() {
+	    try {
+		    custodians = db.transactionWithResult(true,
+				    socialBackupManager::getCustodianContactIds);
+	    } catch (DbException e) {
+	    	custodians = new ArrayList<>();
+	    }
+	    loadContacts();
+    }
+
+	public boolean haveExistingBackup() {
+		try {
+			backupMetadata = db.transactionWithNullableResult(true,
+					socialBackupManager::getBackupMetadata);
+		} catch (DbException e) {
+			return false;
+		}
+		return (backupMetadata != null);
+	}
+
+//	public BackupMetadata getBackupMetadata() {
+//		return backupMetadata;
+//	}
+
+	public boolean haveEnoughContacts() throws DbException {
+		return (contactManager.getContacts().size() > 1);
+	}
+
+	public void setCustodians(List<ContactId> contacts) {
+		custodians = contacts;
+	}
+
+	public void createBackup() {
+		try {
+			db.transaction(false, txn -> {
+				socialBackupManager
+						.createBackup(txn, (List<ContactId>) custodians,
+								threshold);
+			});
+		} catch (DbException e) {
+			state.postValue(State.FAILURE);
+		}
+	}
+
+	public void setThreshold(int threshold) {
+		this.threshold = threshold;
+		createBackup();
+	}
+
+	public void onSuccessDismissed() {
+		state.postValue(State.SUCCESS);
+	}
+
+	public MutableLiveData<State> getState() {
+		return state;
+	}
+
+	public void onExplainerDismissed() {
+		state.postValue(State.CHOOSING_CUSTODIANS);
+	}
+
+	@Override
+	protected boolean displayContact(ContactId contactId) {
+		// Check if contact holds a backup piece
+		return custodians.contains(contactId);
+	}
+
+	public int getThresholdFromExistingBackup() {
+		return backupMetadata.getThreshold();
+	}
+
+	public int getNumberOfCustodiansFromExistingBackup() {
+		return backupMetadata.getCustodians().size();
+	}
+}
+

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

@@ -0,0 +1,225 @@
+package org.briarproject.briar.android.socialbackup;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.text.Spannable;
+import android.text.SpannableString;
+import android.text.SpannableStringBuilder;
+import android.text.style.ImageSpan;
+import android.view.LayoutInflater;
+import android.view.Menu;
+import android.view.MenuInflater;
+import android.view.MenuItem;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.SeekBar;
+import android.widget.TextView;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.briarproject.briar.android.login.StrengthMeter;
+import org.magmacollective.darkcrystal.secretsharingwrapper.SecretSharingWrapper;
+
+import java.util.Arrays;
+
+import javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.appcompat.app.AlertDialog;
+import androidx.lifecycle.ViewModelProvider;
+
+import static android.view.View.GONE;
+
+public class ThresholdSelectorFragment extends BaseFragment {
+
+	public static final String TAG = ThresholdSelectorFragment.class.getName();
+	private static final String NUMBER_CUSTODIANS = "numberCustodians";
+
+	private int numberOfCustodians;
+	private int threshold;
+	private int recommendedThreshold;
+	private SeekBar seekBar;
+	private TextView thresholdRepresentation;
+	private TextView message;
+	private TextView mOfn;
+	private StrengthMeter strengthMeter;
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private SocialBackupSetupViewModel viewModel;
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(SocialBackupSetupViewModel.class);
+	}
+
+	public static ThresholdSelectorFragment newInstance(int numberCustodians) {
+		Bundle bundle = new Bundle();
+		bundle.putInt(NUMBER_CUSTODIANS, numberCustodians);
+		ThresholdSelectorFragment fragment = new ThresholdSelectorFragment();
+		fragment.setArguments(bundle);
+		return fragment;
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		requireActivity().setTitle(R.string.title_define_threshold);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_select_threshold,
+				container, false);
+		Bundle args = requireArguments();
+		numberOfCustodians = args.getInt(NUMBER_CUSTODIANS);
+		seekBar = view.findViewById(R.id.seekBar);
+		thresholdRepresentation =
+				view.findViewById(R.id.textViewThresholdRepresentation);
+		message = view.findViewById(R.id.textViewMessage);
+		mOfn = view.findViewById(R.id.text_view_m_of_n);
+		strengthMeter = view.findViewById(R.id.strength_meter);
+
+		if (numberOfCustodians > 3) {
+			seekBar.setMax(numberOfCustodians -3);
+			seekBar.setOnSeekBarChangeListener(new SeekBarListener());
+			recommendedThreshold =
+					SecretSharingWrapper.defaultThreshold(numberOfCustodians);
+			threshold = recommendedThreshold;
+			seekBar.setProgress(threshold - 2);
+			strengthMeter.setStrength(1);
+		} else {
+			seekBar.setEnabled(false);
+			seekBar.setVisibility(GONE);
+			strengthMeter.setVisibility(GONE);
+			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() {
+		mOfn.setText(String.format(
+				getString(R.string.threshold_m_of_n), threshold,
+				numberOfCustodians));
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+		inflater.inflate(R.menu.define_threshold_actions, menu);
+		super.onCreateOptionsMenu(menu, inflater);
+	}
+
+	@Override
+	public boolean onOptionsItemSelected(MenuItem item) {
+		switch (item.getItemId()) {
+			case R.id.action_threshold_defined:
+				viewModel.setThreshold(threshold);
+				showSuccessDialog();
+				return true;
+			default:
+				return super.onOptionsItemSelected(item);
+		}
+	}
+
+	private void showSuccessDialog() {
+		AlertDialog.Builder builder = new AlertDialog.Builder(requireContext(),
+				R.style.BriarDialogTheme);
+		builder.setTitle(R.string.backup_created);
+		builder.setMessage(R.string.backup_done_info);
+		builder.setPositiveButton(R.string.ok,
+				(dialog, which) -> viewModel.onSuccessDismissed());
+		builder.setIcon(R.drawable.ic_baseline_done_outline_24);
+				AlertDialog dialog = builder.create();
+		dialog.show();
+	}
+
+	private SpannableStringBuilder buildThresholdRepresentationString() {
+		char[] charArray = new char[numberOfCustodians];
+		Arrays.fill(charArray, ' ');
+		SpannableStringBuilder string = new SpannableStringBuilder(new String(charArray));
+
+		for (int i = 0; i < numberOfCustodians; i++) {
+			int drawable = i < threshold
+					? R.drawable.ic_custodian_required
+					: R.drawable.ic_custodian_optional;
+			string.setSpan(new ImageSpan(getContext(), drawable), i,
+					i+1,
+					Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
+		}
+		// If we have more than 6, split it on two lines
+		if (numberOfCustodians > 6) string.insert(4, "\n");
+        return string;
+	}
+
+	private class SeekBarListener implements SeekBar.OnSeekBarChangeListener {
+
+		@Override
+		public void onProgressChanged(SeekBar seekBar, int progress,
+				boolean fromUser) {
+			threshold = progress + 2;
+
+			thresholdRepresentation.setText(
+					buildThresholdRepresentationString()
+			);
+			setmOfnText();
+
+			int sanityLevel = SecretSharingWrapper
+					.thresholdSanity(threshold, numberOfCustodians);
+			int text = R.string.threshold_secure;
+			float strength = 1;
+			if (threshold == recommendedThreshold) {
+				text = R.string.threshold_recommended;
+			}
+			if (sanityLevel < -1) {
+                strength = 0.75f;
+				text = R.string.threshold_low_insecure;
+			}
+			if (sanityLevel < -2) {
+				strength = 0.5f;
+			}
+			if (sanityLevel > 0) {
+				strength = 0.75f;
+				text = R.string.threshold_high_insecure;
+			}
+			strengthMeter.setStrength(strength);
+			message.setText(text);
+		}
+
+		@Override
+		public void onStartTrackingTouch(SeekBar seekBar) {
+			// do nothing
+		}
+
+		@Override
+		public void onStopTrackingTouch(SeekBar seekBar) {
+			// do nothing
+		}
+
+	}
+
+}

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

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

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

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

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

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

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

@@ -0,0 +1,54 @@
+package org.briarproject.briar.android.socialbackup.recover;
+
+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 javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+
+public class CustodianRecoveryModeExplainerFragment extends BaseFragment {
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private CustodianReturnShardViewModel viewModel;
+
+	public static final String TAG =
+			CustodianRecoveryModeExplainerFragment.class.getName();
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(CustodianReturnShardViewModel.class);
+	}
+
+	@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 -> viewModel.onContinueClicked());
+		return view;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+}
+

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/recover/CustodianReturnShardActivity.java

@@ -0,0 +1,126 @@
+package org.briarproject.briar.android.socialbackup.recover;
+
+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.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.recovery.CustodianTask;
+
+import java.io.IOException;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import androidx.fragment.app.FragmentManager;
+import androidx.lifecycle.ViewModelProvider;
+
+import static org.briarproject.briar.android.conversation.ConversationActivity.CONTACT_ID;
+
+public class CustodianReturnShardActivity extends BriarActivity
+		implements BaseFragment.BaseFragmentListener {
+
+	private CustodianReturnShardViewModel viewModel;
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(this, viewModelFactory)
+				.get(CustodianReturnShardViewModel.class);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle state) {
+		super.onCreate(state);
+
+		setContentView(R.layout.activity_fragment_container);
+		if (state == null) {
+			Intent intent = getIntent();
+			int id = intent.getIntExtra(CONTACT_ID, -1);
+			if (id == -1) throw new IllegalStateException("No ContactId");
+			ContactId contactId = new ContactId(id);
+
+			try {
+				viewModel.start(contactId);
+//			} catch (IOException e) {
+//				// TODO improve this
+//				Toast.makeText(this,
+//						"It looks like you are not connected to a Wifi network",
+//						Toast.LENGTH_SHORT).show();
+//				showInitialFragment(new CustodianReturnShardErrorFragment());
+			} catch (DbException e) {
+				Toast.makeText(this,
+						"You do not hold a backup piece for this contact",
+						Toast.LENGTH_SHORT).show();
+				finish();
+			}
+		}
+		showInitialFragment(new CustodianRecoveryModeExplainerFragment());
+
+		viewModel.getContinueClicked().observeEvent(this, clicked -> {
+			if (clicked) beginTransfer();
+		});
+
+		viewModel.getShowCameraFragment().observeEvent(this, show -> {
+			if (show) showCameraFragment();
+		});
+		viewModel.getSuccessDismissed().observeEvent(this, dismissed -> {
+			if (dismissed) finish();
+		});
+		viewModel.getErrorTryAgain().observeEvent(this, tryAgain -> {
+			if (tryAgain) beginTransfer();
+		});
+		viewModel.getState()
+				.observe(this, this::onReturnShardStateChanged);
+	}
+
+	private void beginTransfer() {
+		try {
+			viewModel.beginTransfer();
+		} catch (IOException e) {
+			Toast.makeText(this,
+					"It looks like you are not connected to a Wifi network",
+					Toast.LENGTH_SHORT).show();
+			FragmentManager fm = getSupportFragmentManager();
+			if (fm.findFragmentByTag(CustodianReturnShardFragment.TAG) ==
+					null) {
+				BaseFragment f = new CustodianReturnShardErrorFragment();
+				fm.beginTransaction()
+						.replace(R.id.fragmentContainer, f, f.getUniqueTag())
+						.addToBackStack(f.getUniqueTag())
+						.commit();
+			}
+		}
+	}
+
+	private void onReturnShardStateChanged(CustodianTask.State state) {
+		if (state instanceof CustodianTask.State.Failure) {
+			// TODO error fragment here
+			// TODO handle reason
+			Toast.makeText(this,
+					"Backup piece transfer failed",
+					Toast.LENGTH_SHORT).show();
+			finish();
+		}
+	}
+
+	private void showCameraFragment() {
+		// FIXME #824
+		FragmentManager fm = getSupportFragmentManager();
+		if (fm.findFragmentByTag(CustodianReturnShardFragment.TAG) == null) {
+			BaseFragment f = CustodianReturnShardFragment.newInstance();
+			fm.beginTransaction()
+					.replace(R.id.fragmentContainer, f, f.getUniqueTag())
+					.addToBackStack(f.getUniqueTag())
+					.commit();
+		}
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/recover/CustodianReturnShardErrorFragment.java

@@ -0,0 +1,57 @@
+package org.briarproject.briar.android.socialbackup.recover;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+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.BaseFragment;
+
+import javax.inject.Inject;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class CustodianReturnShardErrorFragment extends BaseFragment {
+	public static final String TAG =
+			CustodianReturnShardErrorFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private CustodianReturnShardViewModel viewModel;
+
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(CustodianReturnShardViewModel.class);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(@NonNull LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View view = inflater.inflate(R.layout.fragment_recovery_custodian_error_explainer,
+				container, false);
+		Button button = view.findViewById(R.id.button);
+		button.setOnClickListener(e -> viewModel.onErrorTryAgain());
+        // TODO cancel button
+//		button.setOnClickListener(e -> viewModel.onErrorCancelled());
+		return view;
+	}
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+}