Merge pull request #7369 from vector-im/feature/hughns/qr_code_login

Implement logic for sign in with QR

changelog.d/7369.feature

@@ -0,0 +1 @@
+Add logic for sign in with QR code

library/ui-strings/src/main/res/values/strings.xml

@@ -3386,9 +3386,16 @@
     <string name="qr_code_login_header_failed_device_is_not_supported_description">Linking with this device is not supported.</string>
     <string name="qr_code_login_header_failed_timeout_description">The linking wasn’t completed in the required time.</string>
     <string name="qr_code_login_header_failed_denied_description">The request was denied on the other device.</string>
-    <string name="qr_code_login_new_device_instruction_1">Open ${app_name} on your other device</string>
-    <string name="qr_code_login_new_device_instruction_2">Go to Settings -> Security &amp; Privacy -> Show All Sessions</string>
-    <string name="qr_code_login_new_device_instruction_3">Select \'Show QR code in this device\'</string>
+    <string name="qr_code_login_header_failed_other_description">The request failed.</string>
+    <string name="qr_code_login_header_failed_e2ee_security_issue_description">A security issue was encountered setting up secure messaging. One of the following may be compromised: Your homeserver; Your internet connection(s); Your device(s);</string>
+    <string name="qr_code_login_header_failed_other_device_already_signed_in_description">The other device is already signed in.</string>
+    <string name="qr_code_login_header_failed_other_device_not_signed_in_description">The other device must be signed in.</string>
+    <string name="qr_code_login_header_failed_invalid_qr_code_description">That QR code is invalid.</string>
+    <string name="qr_code_login_header_failed_user_cancelled_description">The sign in was cancelled on the other device.</string>
+    <string name="qr_code_login_header_failed_homeserver_is_not_supported_description">The homeserver doesn\'t support sign in with QR code.</string>
+    <string name="qr_code_login_new_device_instruction_1">Open the app on your other device</string>
+    <string name="qr_code_login_new_device_instruction_2">Go to Settings -> Security &amp; Privacy</string>
+    <string name="qr_code_login_new_device_instruction_3">Select \'Show QR code\'</string>
     <string name="qr_code_login_link_a_device_scan_qr_code_instruction_1">Start at the sign in screen</string>
     <string name="qr_code_login_link_a_device_scan_qr_code_instruction_2">Select \'Sign in with QR code\'</string>
     <string name="qr_code_login_link_a_device_show_qr_code_instruction_1">Start at the sign in screen</string>

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/logger/LoggerTag.kt

@@ -27,6 +27,7 @@ open class LoggerTag(name: String, parentTag: LoggerTag? = null) {
     object SYNC : LoggerTag("SYNC")
     object VOIP : LoggerTag("VOIP")
     object CRYPTO : LoggerTag("CRYPTO")
+    object RENDEZVOUS : LoggerTag("RZ")
 
     val value: String = if (parentTag == null) {
         name

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/Rendezvous.kt

@@ -0,0 +1,229 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous
+
+import android.net.Uri
+import org.matrix.android.sdk.api.auth.AuthenticationService
+import org.matrix.android.sdk.api.auth.data.HomeServerConnectionConfig
+import org.matrix.android.sdk.api.logger.LoggerTag
+import org.matrix.android.sdk.api.rendezvous.channels.ECDHRendezvousChannel
+import org.matrix.android.sdk.api.rendezvous.model.ECDHRendezvousCode
+import org.matrix.android.sdk.api.rendezvous.model.Outcome
+import org.matrix.android.sdk.api.rendezvous.model.Payload
+import org.matrix.android.sdk.api.rendezvous.model.PayloadType
+import org.matrix.android.sdk.api.rendezvous.model.Protocol
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousIntent
+import org.matrix.android.sdk.api.rendezvous.transports.SimpleHttpRendezvousTransport
+import org.matrix.android.sdk.api.session.Session
+import org.matrix.android.sdk.api.session.crypto.crosssigning.DeviceTrustLevel
+import org.matrix.android.sdk.api.session.crypto.crosssigning.KEYBACKUP_SECRET_SSSS_NAME
+import org.matrix.android.sdk.api.session.crypto.crosssigning.MASTER_KEY_SSSS_NAME
+import org.matrix.android.sdk.api.session.crypto.crosssigning.SELF_SIGNING_KEY_SSSS_NAME
+import org.matrix.android.sdk.api.session.crypto.crosssigning.USER_SIGNING_KEY_SSSS_NAME
+import org.matrix.android.sdk.api.util.MatrixJsonParser
+import timber.log.Timber
+
+/**
+ * Implementation of MSC3906 to sign in + E2EE set up using a QR code.
+ */
+class Rendezvous(
+        val channel: RendezvousChannel,
+        val theirIntent: RendezvousIntent,
+) {
+    companion object {
+        private val TAG = LoggerTag(Rendezvous::class.java.simpleName, LoggerTag.RENDEZVOUS).value
+
+        @Throws(RendezvousError::class)
+        fun buildChannelFromCode(code: String): Rendezvous {
+            val parsed = try {
+                // we rely on moshi validating the code and throwing exception if invalid JSON or doesn't
+                MatrixJsonParser.getMoshi().adapter(ECDHRendezvousCode::class.java).fromJson(code)
+            } catch (a: Throwable) {
+                throw RendezvousError("Invalid code", RendezvousFailureReason.InvalidCode)
+            } ?: throw RendezvousError("Invalid code", RendezvousFailureReason.InvalidCode)
+
+            val transport = SimpleHttpRendezvousTransport(parsed.rendezvous.transport.uri)
+
+            return Rendezvous(
+                    ECDHRendezvousChannel(transport, parsed.rendezvous.key),
+                    parsed.intent
+            )
+        }
+    }
+
+    private val adapter = MatrixJsonParser.getMoshi().adapter(Payload::class.java)
+
+    // not yet implemented: RendezvousIntent.RECIPROCATE_LOGIN_ON_EXISTING_DEVICE
+    val ourIntent: RendezvousIntent = RendezvousIntent.LOGIN_ON_NEW_DEVICE
+
+    @Throws(RendezvousError::class)
+    private suspend fun checkCompatibility() {
+        val incompatible = theirIntent == ourIntent
+
+        Timber.tag(TAG).d("ourIntent: $ourIntent, theirIntent: $theirIntent, incompatible: $incompatible")
+
+        if (incompatible) {
+            // inform the other side
+            send(Payload(PayloadType.FINISH, intent = ourIntent))
+            if (ourIntent == RendezvousIntent.LOGIN_ON_NEW_DEVICE) {
+                throw RendezvousError("The other device isn't signed in", RendezvousFailureReason.OtherDeviceNotSignedIn)
+            } else {
+                throw RendezvousError("The other device is already signed in", RendezvousFailureReason.OtherDeviceAlreadySignedIn)
+            }
+        }
+    }
+
+    @Throws(RendezvousError::class)
+    suspend fun startAfterScanningCode(): String {
+        val checksum = channel.connect()
+
+        Timber.tag(TAG).i("Connected to secure channel with checksum: $checksum")
+
+        checkCompatibility()
+
+        // get protocols
+        Timber.tag(TAG).i("Waiting for protocols")
+        val protocolsResponse = receive()
+
+        if (protocolsResponse?.protocols == null || !protocolsResponse.protocols.contains(Protocol.LOGIN_TOKEN)) {
+            send(Payload(PayloadType.FINISH, outcome = Outcome.UNSUPPORTED))
+            throw RendezvousError("Unsupported protocols", RendezvousFailureReason.UnsupportedHomeserver)
+        }
+
+        send(Payload(PayloadType.PROGRESS, protocol = Protocol.LOGIN_TOKEN))
+
+        return checksum
+    }
+
+    @Throws(RendezvousError::class)
+    suspend fun waitForLoginOnNewDevice(authenticationService: AuthenticationService): Session {
+        Timber.tag(TAG).i("Waiting for login_token")
+
+        val loginToken = receive()
+
+        if (loginToken?.type == PayloadType.FINISH) {
+            when (loginToken.outcome) {
+                Outcome.DECLINED -> {
+                    throw RendezvousError("Login declined by other device", RendezvousFailureReason.UserDeclined)
+                }
+                Outcome.UNSUPPORTED -> {
+                    throw RendezvousError("Homeserver lacks support", RendezvousFailureReason.UnsupportedHomeserver)
+                }
+                else -> {
+                    throw RendezvousError("Unknown error", RendezvousFailureReason.Unknown)
+                }
+            }
+        }
+
+        val homeserver = loginToken?.homeserver ?: throw RendezvousError("No homeserver returned", RendezvousFailureReason.ProtocolError)
+        val token = loginToken.loginToken ?: throw RendezvousError("No login token returned", RendezvousFailureReason.ProtocolError)
+
+        Timber.tag(TAG).i("Got login_token now attempting to sign in with $homeserver")
+
+        val hsConfig = HomeServerConnectionConfig(homeServerUri = Uri.parse(homeserver))
+        return authenticationService.loginUsingQrLoginToken(hsConfig, token)
+    }
+
+    @Throws(RendezvousError::class)
+    suspend fun completeVerificationOnNewDevice(session: Session) {
+        val userId = session.myUserId
+        val crypto = session.cryptoService()
+        val deviceId = crypto.getMyDevice().deviceId
+        val deviceKey = crypto.getMyDevice().fingerprint()
+        send(Payload(PayloadType.PROGRESS, outcome = Outcome.SUCCESS, deviceId = deviceId, deviceKey = deviceKey))
+
+        // await confirmation of verification
+        val verificationResponse = receive()
+        if (verificationResponse?.outcome == Outcome.VERIFIED) {
+            val verifyingDeviceId = verificationResponse.verifyingDeviceId
+                    ?: throw RendezvousError("No verifying device id returned", RendezvousFailureReason.ProtocolError)
+            val verifyingDeviceFromServer = crypto.getCryptoDeviceInfo(userId, verifyingDeviceId)
+            if (verifyingDeviceFromServer?.fingerprint() != verificationResponse.verifyingDeviceKey) {
+                Timber.tag(TAG).w(
+                        "Verifying device $verifyingDeviceId key doesn't match: ${
+                            verifyingDeviceFromServer?.fingerprint()
+                        } vs ${verificationResponse.verifyingDeviceKey})"
+                )
+                // inform the other side
+                send(Payload(PayloadType.FINISH, outcome = Outcome.E2EE_SECURITY_ERROR))
+                throw RendezvousError("Key from verifying device doesn't match", RendezvousFailureReason.E2EESecurityIssue)
+            }
+
+            verificationResponse.masterKey?.let { masterKeyFromVerifyingDevice ->
+                // verifying device provided us with a master key, so use it to check integrity
+
+                // see what the homeserver told us
+                val localMasterKey = crypto.crossSigningService().getMyCrossSigningKeys()?.masterKey()
+
+                // n.b. if no local master key this is a problem, as well as it not matching
+                if (localMasterKey?.unpaddedBase64PublicKey != masterKeyFromVerifyingDevice) {
+                    Timber.tag(TAG).w("Master key from verifying device doesn't match: $masterKeyFromVerifyingDevice vs $localMasterKey")
+                    // inform the other side
+                    send(Payload(PayloadType.FINISH, outcome = Outcome.E2EE_SECURITY_ERROR))
+                    throw RendezvousError("Master key from verifying device doesn't match", RendezvousFailureReason.E2EESecurityIssue)
+                }
+
+                // set other device as verified
+                Timber.tag(TAG).i("Setting device $verifyingDeviceId as verified")
+                crypto.setDeviceVerification(DeviceTrustLevel(locallyVerified = true, crossSigningVerified = false), userId, verifyingDeviceId)
+
+                Timber.tag(TAG).i("Setting master key as trusted")
+                crypto.crossSigningService().markMyMasterKeyAsTrusted()
+            } ?: run {
+                // set other device as verified anyway
+                Timber.tag(TAG).i("Setting device $verifyingDeviceId as verified")
+                crypto.setDeviceVerification(DeviceTrustLevel(locallyVerified = true, crossSigningVerified = false), userId, verifyingDeviceId)
+
+                Timber.tag(TAG).i("No master key given by verifying device")
+            }
+
+            // request secrets from the verifying device
+            Timber.tag(TAG).i("Requesting secrets from $verifyingDeviceId")
+
+            session.sharedSecretStorageService().let {
+                it.requestSecret(MASTER_KEY_SSSS_NAME, verifyingDeviceId)
+                it.requestSecret(SELF_SIGNING_KEY_SSSS_NAME, verifyingDeviceId)
+                it.requestSecret(USER_SIGNING_KEY_SSSS_NAME, verifyingDeviceId)
+                it.requestSecret(KEYBACKUP_SECRET_SSSS_NAME, verifyingDeviceId)
+            }
+        } else {
+            Timber.tag(TAG).i("Not doing verification")
+        }
+    }
+
+    @Throws(RendezvousError::class)
+    private suspend fun receive(): Payload? {
+        val data = channel.receive() ?: return null
+        val payload = try {
+            adapter.fromJson(data.toString(Charsets.UTF_8))
+        } catch (e: Exception) {
+            Timber.tag(TAG).w(e, "Failed to parse payload")
+            throw RendezvousError("Invalid payload received", RendezvousFailureReason.Unknown)
+        }
+
+        return payload
+    }
+
+    private suspend fun send(payload: Payload) {
+        channel.send(adapter.toJson(payload).toByteArray(Charsets.UTF_8))
+    }
+
+    suspend fun close() {
+        channel.close()
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/RendezvousChannel.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous
+
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
+
+/**
+ * Representation of a rendezvous channel such as that described by MSC3903.
+ */
+interface RendezvousChannel {
+    val transport: RendezvousTransport
+
+    /**
+     * @returns the checksum/confirmation digits to be shown to the user
+     */
+    @Throws(RendezvousError::class)
+    suspend fun connect(): String
+
+    /**
+     * Send a payload via the channel.
+     * @param data payload to send
+     */
+    @Throws(RendezvousError::class)
+    suspend fun send(data: ByteArray)
+
+    /**
+     * Receive a payload from the channel.
+     * @returns the received payload
+     */
+    @Throws(RendezvousError::class)
+    suspend fun receive(): ByteArray?
+
+    /**
+     * Closes the channel and cleans up.
+     */
+    suspend fun close()
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/RendezvousFailureReason.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous
+
+enum class RendezvousFailureReason(val canRetry: Boolean = true) {
+    UserDeclined,
+    OtherDeviceNotSignedIn,
+    OtherDeviceAlreadySignedIn,
+    Unknown,
+    Expired,
+    UserCancelled,
+    InvalidCode,
+    UnsupportedAlgorithm(false),
+    UnsupportedTransport(false),
+    UnsupportedHomeserver(false),
+    ProtocolError,
+    E2EESecurityIssue(false)
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/RendezvousTransport.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous
+
+import okhttp3.MediaType
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousTransportDetails
+
+interface RendezvousTransport {
+    var ready: Boolean
+
+    @Throws(RendezvousError::class)
+    suspend fun details(): RendezvousTransportDetails
+
+    @Throws(RendezvousError::class)
+    suspend fun send(contentType: MediaType, data: ByteArray)
+
+    @Throws(RendezvousError::class)
+    suspend fun receive(): ByteArray?
+
+    suspend fun close()
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/channels/ECDHRendezvousChannel.kt

@@ -0,0 +1,183 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.channels
+
+import android.util.Base64
+import com.squareup.moshi.JsonClass
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import okhttp3.MediaType.Companion.toMediaType
+import org.matrix.android.sdk.api.logger.LoggerTag
+import org.matrix.android.sdk.api.rendezvous.RendezvousChannel
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
+import org.matrix.android.sdk.api.rendezvous.RendezvousTransport
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
+import org.matrix.android.sdk.api.rendezvous.model.SecureRendezvousChannelAlgorithm
+import org.matrix.android.sdk.api.util.MatrixJsonParser
+import org.matrix.android.sdk.internal.crypto.verification.SASDefaultVerificationTransaction
+import org.matrix.olm.OlmSAS
+import timber.log.Timber
+import java.security.SecureRandom
+import java.util.LinkedList
+import javax.crypto.Cipher
+import javax.crypto.spec.IvParameterSpec
+import javax.crypto.spec.SecretKeySpec
+
+/**
+ *  Implements X25519 ECDH key agreement and AES-256-GCM encryption channel as per MSC3903:
+ *  https://github.com/matrix-org/matrix-spec-proposals/pull/3903
+ */
+class ECDHRendezvousChannel(override var transport: RendezvousTransport, theirPublicKeyBase64: String?) : RendezvousChannel {
+    companion object {
+        private const val ALGORITHM_SPEC = "AES/GCM/NoPadding"
+        private const val KEY_SPEC = "AES"
+        private val TAG = LoggerTag(ECDHRendezvousChannel::class.java.simpleName, LoggerTag.RENDEZVOUS).value
+    }
+
+    @JsonClass(generateAdapter = true)
+    internal data class ECDHPayload(
+            val algorithm: SecureRendezvousChannelAlgorithm? = null,
+            val key: String? = null,
+            val ciphertext: String? = null,
+            val iv: String? = null
+    )
+
+    private val olmSASMutex = Mutex()
+    private var olmSAS: OlmSAS?
+    private val ourPublicKey: ByteArray
+    private val ecdhAdapter = MatrixJsonParser.getMoshi().adapter(ECDHPayload::class.java)
+    private var theirPublicKey: ByteArray? = null
+    private var aesKey: ByteArray? = null
+
+    init {
+        theirPublicKeyBase64?.let {
+            theirPublicKey = Base64.decode(it, Base64.NO_WRAP)
+        }
+        olmSAS = OlmSAS()
+        ourPublicKey = Base64.decode(olmSAS!!.publicKey, Base64.NO_WRAP)
+    }
+
+    @Throws(RendezvousError::class)
+    override suspend fun connect(): String {
+        val sas = olmSAS ?: throw RendezvousError("Channel closed", RendezvousFailureReason.Unknown)
+        val isInitiator = theirPublicKey == null
+
+        if (isInitiator) {
+            Timber.tag(TAG).i("Waiting for other device to send their public key")
+            val res = this.receiveAsPayload() ?: throw RendezvousError("No reply from other device", RendezvousFailureReason.ProtocolError)
+
+            if (res.key == null) {
+                throw RendezvousError(
+                        "Unsupported algorithm: ${res.algorithm}",
+                        RendezvousFailureReason.UnsupportedAlgorithm,
+                )
+            }
+            theirPublicKey = Base64.decode(res.key, Base64.NO_WRAP)
+        } else {
+            // send our public key unencrypted
+            Timber.tag(TAG).i("Sending public key")
+            send(
+                    ECDHPayload(
+                            algorithm = SecureRendezvousChannelAlgorithm.ECDH_V1,
+                            key = Base64.encodeToString(ourPublicKey, Base64.NO_WRAP)
+                    )
+            )
+        }
+
+        olmSASMutex.withLock {
+            sas.setTheirPublicKey(Base64.encodeToString(theirPublicKey, Base64.NO_WRAP))
+            sas.setTheirPublicKey(Base64.encodeToString(theirPublicKey, Base64.NO_WRAP))
+
+            val initiatorKey = Base64.encodeToString(if (isInitiator) ourPublicKey else theirPublicKey, Base64.NO_WRAP)
+            val recipientKey = Base64.encodeToString(if (isInitiator) theirPublicKey else ourPublicKey, Base64.NO_WRAP)
+            val aesInfo = "${SecureRendezvousChannelAlgorithm.ECDH_V1.value}|$initiatorKey|$recipientKey"
+
+            aesKey = sas.generateShortCode(aesInfo, 32)
+
+            val rawChecksum = sas.generateShortCode(aesInfo, 5)
+            return SASDefaultVerificationTransaction.getDecimalCodeRepresentation(rawChecksum, separator = "-")
+        }
+    }
+
+    private suspend fun send(payload: ECDHPayload) {
+        transport.send("application/json".toMediaType(), ecdhAdapter.toJson(payload).toByteArray(Charsets.UTF_8))
+    }
+
+    override suspend fun send(data: ByteArray) {
+        if (aesKey == null) {
+            throw IllegalStateException("Shared secret not established")
+        }
+        send(encrypt(data))
+    }
+
+    private suspend fun receiveAsPayload(): ECDHPayload? {
+        transport.receive()?.toString(Charsets.UTF_8)?.let {
+            return ecdhAdapter.fromJson(it)
+        } ?: return null
+    }
+
+    override suspend fun receive(): ByteArray? {
+        if (aesKey == null) {
+            throw IllegalStateException("Shared secret not established")
+        }
+        val payload = receiveAsPayload() ?: return null
+        return decrypt(payload)
+    }
+
+    override suspend fun close() {
+        val sas = olmSAS ?: throw IllegalStateException("Channel already closed")
+        olmSASMutex.withLock {
+            // this does a double release check already so we don't re-check ourselves
+            sas.releaseSas()
+            olmSAS = null
+        }
+        transport.close()
+    }
+
+    private fun encrypt(plainText: ByteArray): ECDHPayload {
+        val iv = ByteArray(16)
+        SecureRandom().nextBytes(iv)
+
+        val cipherText = LinkedList<Byte>()
+
+        val encryptCipher = Cipher.getInstance(ALGORITHM_SPEC)
+        val secretKeySpec = SecretKeySpec(aesKey, KEY_SPEC)
+        val ivParameterSpec = IvParameterSpec(iv)
+        encryptCipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec)
+        cipherText.addAll(encryptCipher.update(plainText).toList())
+        cipherText.addAll(encryptCipher.doFinal().toList())
+
+        return ECDHPayload(
+                ciphertext = Base64.encodeToString(cipherText.toByteArray(), Base64.NO_WRAP),
+                iv = Base64.encodeToString(iv, Base64.NO_WRAP)
+        )
+    }
+
+    private fun decrypt(payload: ECDHPayload): ByteArray {
+        val iv = Base64.decode(payload.iv, Base64.NO_WRAP)
+        val encryptCipher = Cipher.getInstance(ALGORITHM_SPEC)
+        val secretKeySpec = SecretKeySpec(aesKey, KEY_SPEC)
+        val ivParameterSpec = IvParameterSpec(iv)
+        encryptCipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec)
+
+        val plainText = LinkedList<Byte>()
+        plainText.addAll(encryptCipher.update(Base64.decode(payload.ciphertext, Base64.NO_WRAP)).toList())
+        plainText.addAll(encryptCipher.doFinal().toList())
+
+        return plainText.toByteArray()
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/ECDHRendezvous.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+data class ECDHRendezvous(
+        val transport: SimpleHttpRendezvousTransportDetails,
+        val algorithm: SecureRendezvousChannelAlgorithm,
+        val key: String
+)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/ECDHRendezvousCode.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+data class ECDHRendezvousCode(
+        val intent: RendezvousIntent,
+        val rendezvous: ECDHRendezvous
+)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/Outcome.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+enum class Outcome(val value: String) {
+    @Json(name = "success")
+    SUCCESS("success"),
+
+    @Json(name = "declined")
+    DECLINED("declined"),
+
+    @Json(name = "unsupported")
+    UNSUPPORTED("unsupported"),
+
+    @Json(name = "verified")
+    VERIFIED("verified"),
+
+    @Json(name = "e2ee_security_error")
+    E2EE_SECURITY_ERROR("e2ee_security_error")
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/Payload.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+internal data class Payload(
+        val type: PayloadType,
+        val intent: RendezvousIntent? = null,
+        val outcome: Outcome? = null,
+        val protocols: List<Protocol>? = null,
+        val protocol: Protocol? = null,
+        val homeserver: String? = null,
+        @Json(name = "login_token") val loginToken: String? = null,
+        @Json(name = "device_id") val deviceId: String? = null,
+        @Json(name = "device_key") val deviceKey: String? = null,
+        @Json(name = "verifying_device_id") val verifyingDeviceId: String? = null,
+        @Json(name = "verifying_device_key") val verifyingDeviceKey: String? = null,
+        @Json(name = "master_key") val masterKey: String? = null
+)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/PayloadType.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+internal enum class PayloadType(val value: String) {
+    @Json(name = "m.login.start")
+    START("m.login.start"),
+
+    @Json(name = "m.login.finish")
+    FINISH("m.login.finish"),
+
+    @Json(name = "m.login.progress")
+    PROGRESS("m.login.progress")
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/Protocol.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+enum class Protocol(val value: String) {
+    @Json(name = "org.matrix.msc3906.login_token")
+    LOGIN_TOKEN("org.matrix.msc3906.login_token")
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/RendezvousError.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
+
+class RendezvousError(val description: String, val reason: RendezvousFailureReason) : Exception(description)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/RendezvousIntent.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+enum class RendezvousIntent {
+    @Json(name = "login.start") LOGIN_ON_NEW_DEVICE,
+    @Json(name = "login.reciprocate") RECIPROCATE_LOGIN_ON_EXISTING_DEVICE
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/RendezvousTransportDetails.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022 New Vector Ltd
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,10 +14,11 @@
  * limitations under the License.
  */
 
-package im.vector.app.features.login.qr
+package org.matrix.android.sdk.api.rendezvous.model
 
-enum class QrCodeLoginErrorType {
-    DEVICE_IS_NOT_SUPPORTED,
-    TIMEOUT,
-    REQUEST_WAS_DENIED,
-}
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+open class RendezvousTransportDetails(
+    val type: RendezvousTransportType
+)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/RendezvousTransportType.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+enum class RendezvousTransportType(val value: String) {
+    @Json(name = "org.matrix.msc3886.http.v1")
+    MSC3886_SIMPLE_HTTP_V1("org.matrix.msc3886.http.v1")
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/SecureRendezvousChannelAlgorithm.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+enum class SecureRendezvousChannelAlgorithm(val value: String) {
+    @Json(name = "org.matrix.msc3903.rendezvous.v1.curve25519-aes-sha256")
+    ECDH_V1("org.matrix.msc3903.rendezvous.v1.curve25519-aes-sha256")
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/model/SimpleHttpRendezvousTransportDetails.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.model
+
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+data class SimpleHttpRendezvousTransportDetails(
+        val uri: String
+) : RendezvousTransportDetails(type = RendezvousTransportType.MSC3886_SIMPLE_HTTP_V1)

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/rendezvous/transports/SimpleHttpRendezvousTransport.kt

@@ -0,0 +1,173 @@
+/*
+ * Copyright 2022 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.rendezvous.transports
+
+import kotlinx.coroutines.delay
+import okhttp3.MediaType
+import okhttp3.Request
+import okhttp3.RequestBody.Companion.toRequestBody
+import org.matrix.android.sdk.api.logger.LoggerTag
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
+import org.matrix.android.sdk.api.rendezvous.RendezvousTransport
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousTransportDetails
+import org.matrix.android.sdk.api.rendezvous.model.SimpleHttpRendezvousTransportDetails
+import timber.log.Timber
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
+
+/**
+ * Implementation of the Simple HTTP transport MSC3886: https://github.com/matrix-org/matrix-spec-proposals/pull/3886
+ */
+class SimpleHttpRendezvousTransport(rendezvousUri: String?) : RendezvousTransport {
+    companion object {
+        private val TAG = LoggerTag(SimpleHttpRendezvousTransport::class.java.simpleName, LoggerTag.RENDEZVOUS).value
+    }
+
+    override var ready = false
+    private var cancelled = false
+    private var uri: String?
+    private var etag: String? = null
+    private var expiresAt: Date? = null
+
+    init {
+        uri = rendezvousUri
+    }
+
+    override suspend fun details(): RendezvousTransportDetails {
+        val uri = uri ?: throw IllegalStateException("Rendezvous not set up")
+
+        return SimpleHttpRendezvousTransportDetails(uri)
+    }
+
+    @Throws(RendezvousError::class)
+    override suspend fun send(contentType: MediaType, data: ByteArray) {
+        if (cancelled) {
+            throw IllegalStateException("Rendezvous cancelled")
+        }
+
+        val method = if (uri != null) "PUT" else "POST"
+        val uri = this.uri ?: throw RuntimeException("No rendezvous URI")
+
+        val httpClient = okhttp3.OkHttpClient.Builder().build()
+
+        val request = Request.Builder()
+                .url(uri)
+                .method(method, data.toRequestBody())
+                .header("content-type", contentType.toString())
+
+        etag?.let {
+            request.header("if-match", it)
+        }
+
+        val response = httpClient.newCall(request.build()).execute()
+
+        if (response.code == 404) {
+            throw get404Error()
+        }
+        etag = response.header("etag")
+
+        Timber.tag(TAG).i("Sent data to $uri new etag $etag")
+
+        if (method == "POST") {
+            val location = response.header("location") ?: throw RuntimeException("No rendezvous URI found in response")
+
+            response.header("expires")?.let {
+                val format = SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.US)
+                expiresAt = format.parse(it)
+            }
+
+            // resolve location header which could be relative or absolute
+            this.uri = response.request.url.toUri().resolve(location).toString()
+            ready = true
+        }
+    }
+
+    @Throws(RendezvousError::class)
+    override suspend fun receive(): ByteArray? {
+        if (cancelled) {
+            throw IllegalStateException("Rendezvous cancelled")
+        }
+        val uri = uri ?: throw IllegalStateException("Rendezvous not set up")
+        val httpClient = okhttp3.OkHttpClient.Builder().build()
+        while (true) {
+            Timber.tag(TAG).i("Polling: $uri after etag $etag")
+            val request = Request.Builder()
+                    .url(uri)
+                    .get()
+
+            etag?.let {
+                request.header("if-none-match", it)
+            }
+
+            val response = httpClient.newCall(request.build()).execute()
+
+            try {
+                // expired
+                if (response.code == 404) {
+                    throw get404Error()
+                }
+
+                // rely on server expiring the channel rather than checking ourselves
+
+                if (response.header("content-type") != "application/json") {
+                    response.header("etag")?.let {
+                        etag = it
+                    }
+                } else if (response.code == 200) {
+                    response.header("etag")?.let {
+                        etag = it
+                    }
+                    return response.body?.bytes()
+                }
+
+                // sleep for a second before polling again
+                // we rely on the server expiring the channel rather than checking it ourselves
+                delay(1000)
+            } finally {
+                response.close()
+            }
+        }
+    }
+
+    private fun get404Error(): RendezvousError {
+        if (expiresAt != null && Date() > expiresAt) {
+            return RendezvousError("Expired", RendezvousFailureReason.Expired)
+        }
+
+        return RendezvousError("Received unexpected 404", RendezvousFailureReason.Unknown)
+    }
+
+    override suspend fun close() {
+        cancelled = true
+        ready = false
+
+        uri?.let {
+            try {
+                val httpClient = okhttp3.OkHttpClient.Builder().build()
+                val request = Request.Builder()
+                        .url(it)
+                        .delete()
+                        .build()
+                httpClient.newCall(request).execute()
+            } catch (e: Throwable) {
+                Timber.tag(TAG).w(e, "Failed to delete channel")
+            }
+        }
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/verification/SASDefaultVerificationTransaction.kt

@@ -82,6 +82,33 @@ internal abstract class SASDefaultVerificationTransaction(
         // older devices have limited support of emoji but SDK offers images for the 64 verification emojis
         // so always send that we support EMOJI
         val KNOWN_SHORT_CODES = listOf(SasMode.EMOJI, SasMode.DECIMAL)
+
+        /**
+         * decimal: generate five bytes by using HKDF.
+         * Take the first 13 bits and convert it to a decimal number (which will be a number between 0 and 8191 inclusive),
+         * and add 1000 (resulting in a number between 1000 and 9191 inclusive).
+         * Do the same with the second 13 bits, and the third 13 bits, giving three 4-digit numbers.
+         * In other words, if the five bytes are B0, B1, B2, B3, and B4, then the first number is (B0 << 5 | B1 >> 3) + 1000,
+         * the second number is ((B1 & 0x7) << 10 | B2 << 2 | B3 >> 6) + 1000, and the third number is ((B3 & 0x3f) << 7 | B4 >> 1) + 1000.
+         * (This method of converting 13 bits at a time is used to avoid requiring 32-bit clients to do big-number arithmetic,
+         * and adding 1000 to the number avoids having clients to worry about properly zero-padding the number when displaying to the user.)
+         * The three 4-digit numbers are displayed to the user either with dashes (or another appropriate separator) separating the three numbers,
+         * or with the three numbers on separate lines.
+         */
+        fun getDecimalCodeRepresentation(byteArray: ByteArray, separator: String = " "): String {
+            val b0 = byteArray[0].toUnsignedInt() // need unsigned byte
+            val b1 = byteArray[1].toUnsignedInt() // need unsigned byte
+            val b2 = byteArray[2].toUnsignedInt() // need unsigned byte
+            val b3 = byteArray[3].toUnsignedInt() // need unsigned byte
+            val b4 = byteArray[4].toUnsignedInt() // need unsigned byte
+            // (B0 << 5 | B1 >> 3) + 1000
+            val first = (b0.shl(5) or b1.shr(3)) + 1000
+            // ((B1 & 0x7) << 10 | B2 << 2 | B3 >> 6) + 1000
+            val second = ((b1 and 0x7).shl(10) or b2.shl(2) or b3.shr(6)) + 1000
+            // ((B3 & 0x3f) << 7 | B4 >> 1) + 1000
+            val third = ((b3 and 0x3f).shl(7) or b4.shr(1)) + 1000
+            return "$first$separator$second$separator$third"
+        }
     }
 
     override var state: VerificationTxState = VerificationTxState.None
@@ -371,33 +398,6 @@ internal abstract class SASDefaultVerificationTransaction(
         return getDecimalCodeRepresentation(shortCodeBytes!!)
     }
 
-    /**
-     * decimal: generate five bytes by using HKDF.
-     * Take the first 13 bits and convert it to a decimal number (which will be a number between 0 and 8191 inclusive),
-     * and add 1000 (resulting in a number between 1000 and 9191 inclusive).
-     * Do the same with the second 13 bits, and the third 13 bits, giving three 4-digit numbers.
-     * In other words, if the five bytes are B0, B1, B2, B3, and B4, then the first number is (B0 << 5 | B1 >> 3) + 1000,
-     * the second number is ((B1 & 0x7) << 10 | B2 << 2 | B3 >> 6) + 1000, and the third number is ((B3 & 0x3f) << 7 | B4 >> 1) + 1000.
-     * (This method of converting 13 bits at a time is used to avoid requiring 32-bit clients to do big-number arithmetic,
-     * and adding 1000 to the number avoids having clients to worry about properly zero-padding the number when displaying to the user.)
-     * The three 4-digit numbers are displayed to the user either with dashes (or another appropriate separator) separating the three numbers,
-     * or with the three numbers on separate lines.
-     */
-    fun getDecimalCodeRepresentation(byteArray: ByteArray): String {
-        val b0 = byteArray[0].toUnsignedInt() // need unsigned byte
-        val b1 = byteArray[1].toUnsignedInt() // need unsigned byte
-        val b2 = byteArray[2].toUnsignedInt() // need unsigned byte
-        val b3 = byteArray[3].toUnsignedInt() // need unsigned byte
-        val b4 = byteArray[4].toUnsignedInt() // need unsigned byte
-        // (B0 << 5 | B1 >> 3) + 1000
-        val first = (b0.shl(5) or b1.shr(3)) + 1000
-        // ((B1 & 0x7) << 10 | B2 << 2 | B3 >> 6) + 1000
-        val second = ((b1 and 0x7).shl(10) or b2.shl(2) or b3.shr(6)) + 1000
-        // ((B3 & 0x3f) << 7 | B4 >> 1) + 1000
-        val third = ((b3 and 0x3f).shl(7) or b4.shr(1)) + 1000
-        return "$first $second $third"
-    }
-
     override fun getEmojiCodeRepresentation(): List<EmojiRepresentation> {
         return getEmojiCodeRepresentation(shortCodeBytes!!)
     }

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginAction.kt

@@ -22,4 +22,5 @@ sealed class QrCodeLoginAction : VectorViewModelAction {
     data class OnQrCodeScanned(val qrCode: String) : QrCodeLoginAction()
     object GenerateQrCode : QrCodeLoginAction()
     object ShowQrCode : QrCodeLoginAction()
+    object TryAgain : QrCodeLoginAction()
 }

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginActivity.kt

@@ -24,7 +24,9 @@ import com.airbnb.mvrx.Mavericks
 import com.airbnb.mvrx.viewModel
 import dagger.hilt.android.AndroidEntryPoint
 import im.vector.app.core.extensions.addFragment
+import im.vector.app.core.extensions.replaceFragment
 import im.vector.app.core.platform.SimpleFragmentActivity
+import im.vector.app.features.home.HomeActivity
 import im.vector.lib.core.utils.compat.getParcelableCompat
 import timber.log.Timber
 
@@ -37,32 +39,35 @@ class QrCodeLoginActivity : SimpleFragmentActivity() {
         super.onCreate(savedInstanceState)
         views.toolbar.visibility = View.GONE
 
-        val qrCodeLoginArgs: QrCodeLoginArgs? = intent?.extras?.getParcelableCompat(Mavericks.KEY_ARG)
         if (isFirstCreation()) {
-            when (qrCodeLoginArgs?.loginType) {
-                QrCodeLoginType.LOGIN -> {
-                    showInstructionsFragment(qrCodeLoginArgs)
-                }
-                QrCodeLoginType.LINK_A_DEVICE -> {
-                    if (qrCodeLoginArgs.showQrCodeImmediately) {
-                        handleNavigateToShowQrCodeScreen()
-                    } else {
-                        showInstructionsFragment(qrCodeLoginArgs)
-                    }
-                }
-                null -> {
-                    Timber.i("QrCodeLoginArgs is null. This is not expected.")
-                    finish()
-                    return
-                }
-            }
+           navigateToInitialFragment()
         }
 
         observeViewEvents()
     }
 
+    private fun navigateToInitialFragment() {
+        val qrCodeLoginArgs: QrCodeLoginArgs? = intent?.extras?.getParcelableCompat(Mavericks.KEY_ARG)
+        when (qrCodeLoginArgs?.loginType) {
+            QrCodeLoginType.LOGIN -> {
+                showInstructionsFragment(qrCodeLoginArgs)
+            }
+            QrCodeLoginType.LINK_A_DEVICE -> {
+                if (qrCodeLoginArgs.showQrCodeImmediately) {
+                    handleNavigateToShowQrCodeScreen()
+                } else {
+                    showInstructionsFragment(qrCodeLoginArgs)
+                }
+            }
+            null -> {
+                Timber.i("QrCodeLoginArgs is null. This is not expected.")
+                finish()
+            }
+        }
+    }
+
     private fun showInstructionsFragment(qrCodeLoginArgs: QrCodeLoginArgs) {
-        addFragment(
+        replaceFragment(
                 views.container,
                 QrCodeLoginInstructionsFragment::class.java,
                 qrCodeLoginArgs,
@@ -75,10 +80,16 @@ class QrCodeLoginActivity : SimpleFragmentActivity() {
             when (it) {
                 QrCodeLoginViewEvents.NavigateToStatusScreen -> handleNavigateToStatusScreen()
                 QrCodeLoginViewEvents.NavigateToShowQrCodeScreen -> handleNavigateToShowQrCodeScreen()
+                QrCodeLoginViewEvents.NavigateToHomeScreen -> handleNavigateToHomeScreen()
+                QrCodeLoginViewEvents.NavigateToInitialScreen -> handleNavigateToInitialScreen()
             }
         }
     }
 
+    private fun handleNavigateToInitialScreen() {
+        navigateToInitialFragment()
+    }
+
     private fun handleNavigateToShowQrCodeScreen() {
         addFragment(
                 views.container,
@@ -95,6 +106,11 @@ class QrCodeLoginActivity : SimpleFragmentActivity() {
         )
     }
 
+    private fun handleNavigateToHomeScreen() {
+        val intent = HomeActivity.newIntent(this, firstStartMainActivity = false, existingSession = true)
+        startActivity(intent)
+    }
+
     companion object {
 
         private const val FRAGMENT_QR_CODE_INSTRUCTIONS_TAG = "FRAGMENT_QR_CODE_INSTRUCTIONS_TAG"

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginConnectionStatus.kt

@@ -16,9 +16,11 @@
 
 package im.vector.app.features.login.qr
 
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
+
 sealed class QrCodeLoginConnectionStatus {
     object ConnectingToDevice : QrCodeLoginConnectionStatus()
     data class Connected(val securityCode: String, val canConfirmSecurityCode: Boolean) : QrCodeLoginConnectionStatus()
     object SigningIn : QrCodeLoginConnectionStatus()
-    data class Failed(val errorType: QrCodeLoginErrorType, val canTryAgain: Boolean) : QrCodeLoginConnectionStatus()
+    data class Failed(val errorType: RendezvousFailureReason, val canTryAgain: Boolean) : QrCodeLoginConnectionStatus()
 }

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginInstructionsFragment.kt

@@ -63,6 +63,7 @@ class QrCodeLoginInstructionsFragment : VectorBaseFragment<FragmentQrCodeLoginIn
             val scannedQrCode = QrCodeScannerActivity.getResultText(activityResult.data)
             val wasQrCode = QrCodeScannerActivity.getResultIsQrCode(activityResult.data)
 
+            Timber.d("Scanned QR code: $scannedQrCode, was QR code: $wasQrCode")
             if (wasQrCode && !scannedQrCode.isNullOrBlank()) {
                 onQrCodeScanned(scannedQrCode)
             } else {
@@ -76,7 +77,11 @@ class QrCodeLoginInstructionsFragment : VectorBaseFragment<FragmentQrCodeLoginIn
     }
 
     private fun onQrCodeScannerFailed() {
-        Timber.d("QrCodeLoginInstructionsFragment.onQrCodeScannerFailed")
+        // The user scanned something unexpected, so we try scanning again.
+        // This seems to happen particularly with the large QRs needed for rendezvous
+        // especially when the QR is partially off the screen
+        Timber.d("QrCodeLoginInstructionsFragment.onQrCodeScannerFailed - showing scanner again")
+        QrCodeScannerActivity.startForResult(requireActivity(), scanActivityResultLauncher)
     }
 
     override fun invalidate() = withState(viewModel) { state ->

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginStatusFragment.kt

@@ -28,6 +28,7 @@ import im.vector.app.R
 import im.vector.app.core.platform.VectorBaseFragment
 import im.vector.app.databinding.FragmentQrCodeLoginStatusBinding
 import im.vector.app.features.themes.ThemeUtils
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
 
 @AndroidEntryPoint
 class QrCodeLoginStatusFragment : VectorBaseFragment<FragmentQrCodeLoginStatusBinding>() {
@@ -41,6 +42,13 @@ class QrCodeLoginStatusFragment : VectorBaseFragment<FragmentQrCodeLoginStatusBi
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
         initCancelButton()
+        initTryAgainButton()
+    }
+
+    private fun initTryAgainButton() {
+        views.qrCodeLoginStatusTryAgainButton.debouncedClicks {
+            viewModel.handle(QrCodeLoginAction.TryAgain)
+        }
     }
 
     private fun initCancelButton() {
@@ -58,18 +66,26 @@ class QrCodeLoginStatusFragment : VectorBaseFragment<FragmentQrCodeLoginStatusBi
         views.qrCodeLoginStatusCancelButton.isVisible = true
         views.qrCodeLoginStatusTryAgainButton.isVisible = connectionStatus.canTryAgain
         views.qrCodeLoginStatusHeaderView.setTitle(getString(R.string.qr_code_login_header_failed_title))
-        views.qrCodeLoginStatusHeaderView.setDescription(getErrorCode(connectionStatus.errorType))
+        views.qrCodeLoginStatusHeaderView.setDescription(getErrorDescription(connectionStatus.errorType))
         views.qrCodeLoginStatusHeaderView.setImage(
                 imageResource = R.drawable.ic_qr_code_login_failed,
                 backgroundTintColor = ThemeUtils.getColor(requireContext(), R.attr.colorError)
         )
     }
 
-    private fun getErrorCode(errorType: QrCodeLoginErrorType): String {
-        return when (errorType) {
-            QrCodeLoginErrorType.DEVICE_IS_NOT_SUPPORTED -> getString(R.string.qr_code_login_header_failed_device_is_not_supported_description)
-            QrCodeLoginErrorType.TIMEOUT -> getString(R.string.qr_code_login_header_failed_timeout_description)
-            QrCodeLoginErrorType.REQUEST_WAS_DENIED -> getString(R.string.qr_code_login_header_failed_denied_description)
+    private fun getErrorDescription(reason: RendezvousFailureReason): String {
+        return when (reason) {
+            RendezvousFailureReason.UnsupportedAlgorithm,
+            RendezvousFailureReason.UnsupportedTransport -> getString(R.string.qr_code_login_header_failed_device_is_not_supported_description)
+            RendezvousFailureReason.UnsupportedHomeserver -> getString(R.string.qr_code_login_header_failed_homeserver_is_not_supported_description)
+            RendezvousFailureReason.Expired -> getString(R.string.qr_code_login_header_failed_timeout_description)
+            RendezvousFailureReason.UserDeclined -> getString(R.string.qr_code_login_header_failed_denied_description)
+            RendezvousFailureReason.E2EESecurityIssue -> getString(R.string.qr_code_login_header_failed_e2ee_security_issue_description)
+            RendezvousFailureReason.OtherDeviceAlreadySignedIn -> getString(R.string.qr_code_login_header_failed_other_device_already_signed_in_description)
+            RendezvousFailureReason.OtherDeviceNotSignedIn -> getString(R.string.qr_code_login_header_failed_other_device_not_signed_in_description)
+            RendezvousFailureReason.InvalidCode -> getString(R.string.qr_code_login_header_failed_invalid_qr_code_description)
+            RendezvousFailureReason.UserCancelled -> getString(R.string.qr_code_login_header_failed_user_cancelled_description)
+            else -> getString(R.string.qr_code_login_header_failed_other_description)
         }
     }
 

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginViewEvents.kt

@@ -21,4 +21,6 @@ import im.vector.app.core.platform.VectorViewEvents
 sealed class QrCodeLoginViewEvents : VectorViewEvents {
     object NavigateToStatusScreen : QrCodeLoginViewEvents()
     object NavigateToShowQrCodeScreen : QrCodeLoginViewEvents()
+    object NavigateToHomeScreen : QrCodeLoginViewEvents()
+    object NavigateToInitialScreen : QrCodeLoginViewEvents()
 }

vector/src/main/java/im/vector/app/features/login/qr/QrCodeLoginViewModel.kt

@@ -20,13 +20,24 @@ import com.airbnb.mvrx.MavericksViewModelFactory
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import im.vector.app.core.di.ActiveSessionHolder
 import im.vector.app.core.di.MavericksAssistedViewModelFactory
 import im.vector.app.core.di.hiltMavericksViewModelFactory
 import im.vector.app.core.platform.VectorViewModel
+import im.vector.app.core.session.ConfigureAndStartSessionUseCase
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import org.matrix.android.sdk.api.auth.AuthenticationService
+import org.matrix.android.sdk.api.rendezvous.Rendezvous
+import org.matrix.android.sdk.api.rendezvous.RendezvousFailureReason
+import org.matrix.android.sdk.api.rendezvous.model.RendezvousError
 import timber.log.Timber
 
 class QrCodeLoginViewModel @AssistedInject constructor(
         @Assisted private val initialState: QrCodeLoginViewState,
+        private val authenticationService: AuthenticationService,
+        private val activeSessionHolder: ActiveSessionHolder,
+        private val configureAndStartSessionUseCase: ConfigureAndStartSessionUseCase,
 ) : VectorViewModel<QrCodeLoginViewState, QrCodeLoginAction, QrCodeLoginViewEvents>(initialState) {
 
     @AssistedFactory
@@ -34,16 +45,28 @@ class QrCodeLoginViewModel @AssistedInject constructor(
         override fun create(initialState: QrCodeLoginViewState): QrCodeLoginViewModel
     }
 
-    companion object : MavericksViewModelFactory<QrCodeLoginViewModel, QrCodeLoginViewState> by hiltMavericksViewModelFactory()
+    companion object : MavericksViewModelFactory<QrCodeLoginViewModel, QrCodeLoginViewState> by hiltMavericksViewModelFactory() {
+        val TAG: String = QrCodeLoginViewModel::class.java.simpleName
+    }
 
     override fun handle(action: QrCodeLoginAction) {
         when (action) {
             is QrCodeLoginAction.OnQrCodeScanned -> handleOnQrCodeScanned(action)
             QrCodeLoginAction.GenerateQrCode -> handleQrCodeViewStarted()
             QrCodeLoginAction.ShowQrCode -> handleShowQrCode()
+            QrCodeLoginAction.TryAgain -> handleTryAgain()
         }
     }
 
+    private fun handleTryAgain() {
+        setState {
+            copy(
+                    connectionStatus = null
+            )
+        }
+        _viewEvents.post(QrCodeLoginViewEvents.NavigateToInitialScreen)
+    }
+
     private fun handleShowQrCode() {
         _viewEvents.post(QrCodeLoginViewEvents.NavigateToShowQrCodeScreen)
     }
@@ -58,20 +81,60 @@ class QrCodeLoginViewModel @AssistedInject constructor(
     }
 
     private fun handleOnQrCodeScanned(action: QrCodeLoginAction.OnQrCodeScanned) {
-        if (isValidQrCode(action.qrCode)) {
-            setState {
-                copy(
-                        connectionStatus = QrCodeLoginConnectionStatus.ConnectingToDevice
-                )
+        Timber.tag(TAG).d("Scanned code of length ${action.qrCode.length}")
+
+        val rendezvous = try { Rendezvous.buildChannelFromCode(action.qrCode) } catch (t: Throwable) {
+            Timber.tag(TAG).e(t, "Error occurred during sign in")
+            if (t is RendezvousError) {
+                onFailed(t.reason)
+            } else {
+                onFailed(RendezvousFailureReason.Unknown)
+            }
+            return
+        }
+
+        setState {
+            copy(
+                    connectionStatus = QrCodeLoginConnectionStatus.ConnectingToDevice
+            )
+        }
+
+        _viewEvents.post(QrCodeLoginViewEvents.NavigateToStatusScreen)
+
+        viewModelScope.launch(Dispatchers.IO) {
+            try {
+                val confirmationCode = rendezvous.startAfterScanningCode()
+                Timber.tag(TAG).i("Established secure channel with checksum: $confirmationCode")
+
+                onConnectionEstablished(confirmationCode)
+
+                val session = rendezvous.waitForLoginOnNewDevice(authenticationService)
+                onSigningIn()
+
+                activeSessionHolder.setActiveSession(session)
+                authenticationService.reset()
+                configureAndStartSessionUseCase.execute(session)
+
+                rendezvous.completeVerificationOnNewDevice(session)
+
+                _viewEvents.post(QrCodeLoginViewEvents.NavigateToHomeScreen)
+            } catch (t: Throwable) {
+                Timber.tag(TAG).e(t, "Error occurred during sign in")
+                if (t is RendezvousError) {
+                    onFailed(t.reason)
+                } else {
+                    onFailed(RendezvousFailureReason.Unknown)
+                }
             }
-            _viewEvents.post(QrCodeLoginViewEvents.NavigateToStatusScreen)
         }
     }
 
-    private fun onFailed(errorType: QrCodeLoginErrorType, canTryAgain: Boolean) {
+    private fun onFailed(reason: RendezvousFailureReason) {
+        _viewEvents.post(QrCodeLoginViewEvents.NavigateToStatusScreen)
+
         setState {
             copy(
-                    connectionStatus = QrCodeLoginConnectionStatus.Failed(errorType, canTryAgain)
+                    connectionStatus = QrCodeLoginConnectionStatus.Failed(reason, reason.canRetry)
             )
         }
     }
@@ -93,14 +156,11 @@ class QrCodeLoginViewModel @AssistedInject constructor(
         }
     }
 
-    // TODO. Implement in the logic related PR.
-    private fun isValidQrCode(qrCode: String): Boolean {
-        Timber.d("isValidQrCode: $qrCode")
-        return false
-    }
-
-    // TODO. Implement in the logic related PR.
+    /**
+     * QR code generation is not currently supported and this is a placeholder for future
+     * functionality.
+     */
     private fun generateQrCodeData(): String {
-        return "TODO"
+        return "NOT SUPPORTED"
     }
 }