Merge branch '2397-wrong-type-of-qr-code' into 'master'

Show appropriate error message if user scans wrong kind of QR code

Closes #2397

See merge request briar/briar!1748

bramble-api/src/main/java/org/briarproject/bramble/api/keyagreement/KeyAgreementConstants.java

@@ -1,18 +1,26 @@
 package org.briarproject.bramble.api.keyagreement;
 
-public interface KeyAgreementConstants {
+import org.briarproject.bramble.api.mailbox.MailboxConstants;
 
-	/**
+public interface KeyAgreementConstants {
-	 * The version of the BQP protocol used in beta releases. This version
-	 * number is reserved.
-	 */
-	byte BETA_PROTOCOL_VERSION = 89;
 
 	/**
 	 * The current version of the BQP protocol.
 	 */
 	byte PROTOCOL_VERSION = 4;
 
+	/**
+	 * The QR code format identifier, used to distinguish BQP QR codes from
+	 * QR codes used for other purposes. See
+	 * {@link MailboxConstants#QR_FORMAT_ID}.
+	 */
+	byte QR_FORMAT_ID = 0;
+
+	/**
+	 * The QR code format version.
+	 */
+	byte QR_FORMAT_VERSION = PROTOCOL_VERSION;
+
 	/**
 	 * The length of the BQP key commitment in bytes.
 	 */

bramble-api/src/main/java/org/briarproject/bramble/api/keyagreement/PayloadParser.java

@@ -7,5 +7,5 @@ import java.io.IOException;
 @NotNullByDefault
 public interface PayloadParser {
 
-	Payload parse(byte[] raw) throws IOException;
+	Payload parse(String payload) throws IOException;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxConstants.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.api.mailbox;
 
+import org.briarproject.bramble.api.keyagreement.KeyAgreementConstants;
 import org.briarproject.bramble.api.plugin.TransportId;
 
 import java.util.List;
@@ -19,6 +20,18 @@ public interface MailboxConstants {
 	 */
 	TransportId ID = new TransportId("org.briarproject.bramble.mailbox");
 
+	/**
+	 * The QR code format identifier, used to distinguish mailbox QR codes
+	 * from QR codes used for other purposes. See
+	 * {@link KeyAgreementConstants#QR_FORMAT_ID};
+	 */
+	byte QR_FORMAT_ID = 1;
+
+	/**
+	 * The QR code format version.
+	 */
+	byte QR_FORMAT_VERSION = 0;
+
 	/**
 	 * Mailbox API versions that we support as a client. This is reported to our
 	 * contacts by {@link MailboxUpdateManager}.

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxPairingState.java

@@ -1,5 +1,7 @@
 package org.briarproject.bramble.api.mailbox;
 
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
+
 public abstract class MailboxPairingState {
 
 	public abstract static class Pending extends MailboxPairingState {
@@ -29,6 +31,14 @@ public abstract class MailboxPairingState {
 	}
 
 	public static class InvalidQrCode extends MailboxPairingState {
+
+		public final QrCodeType qrCodeType;
+		public final int formatVersion;
+
+		public InvalidQrCode(QrCodeType qrCodeType, int formatVersion) {
+			this.qrCodeType = qrCodeType;
+			this.formatVersion = formatVersion;
+		}
 	}
 
 	public static class MailboxAlreadyPaired extends MailboxPairingState {

bramble-api/src/main/java/org/briarproject/bramble/api/qrcode/QrCodeClassifier.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.api.qrcode;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface QrCodeClassifier {
+
+	enum QrCodeType {
+		BQP,
+		MAILBOX,
+		UNKNOWN
+	}
+
+	Pair<QrCodeType, Integer> classifyQrCode(String payload);
+}

bramble-api/src/main/java/org/briarproject/bramble/api/qrcode/WrongQrCodeTypeException.java

@@ -0,0 +1,25 @@
+package org.briarproject.bramble.api.qrcode;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
+import org.briarproject.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * Thrown when a QR code that has been scanned does not have the expected type.
+ */
+@Immutable
+@NotNullByDefault
+public class WrongQrCodeTypeException extends FormatException {
+
+	private final QrCodeType qrCodeType;
+
+	public WrongQrCodeTypeException(QrCodeType qrCodeType) {
+		this.qrCodeType = qrCodeType;
+	}
+
+	public QrCodeType getQrCodeType() {
+		return qrCodeType;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/util/StringUtils.java

@@ -3,7 +3,6 @@ package org.briarproject.bramble.util;
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.nullsafety.NotNullByDefault;
 
-import java.io.UnsupportedEncodingException;
 import java.nio.ByteBuffer;
 import java.nio.charset.CharacterCodingException;
 import java.nio.charset.Charset;
@@ -17,13 +16,18 @@ import javax.annotation.Nullable;
 import static java.nio.charset.CodingErrorAction.IGNORE;
 import static java.util.regex.Pattern.CASE_INSENSITIVE;
 
+@SuppressWarnings("CharsetObjectCanBeUsed")
 @NotNullByDefault
 public class StringUtils {
 
-	private static final Charset UTF_8 = Charset.forName("UTF-8");
+	public static final Charset UTF_8 = Charset.forName("UTF-8");
-	private static Pattern MAC = Pattern.compile("[0-9a-f]{2}:[0-9a-f]{2}:" +
+	public static final Charset US_ASCII = Charset.forName("US-ASCII");
-					"[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}",
+	public static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
-			CASE_INSENSITIVE);
+
+	private static final Pattern MAC =
+			Pattern.compile("[0-9a-f]{2}:[0-9a-f]{2}:" +
+							"[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}",
+					CASE_INSENSITIVE);
 
 	private static final char[] HEX = new char[] {
 			'0', '1', '2', '3', '4', '5', '6', '7',
@@ -45,11 +49,7 @@ public class StringUtils {
 	}
 
 	public static byte[] toUtf8(String s) {
-		try {
+		return s.getBytes(UTF_8);
-			return s.getBytes("UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new AssertionError(e);
-		}
 	}
 
 	public static String fromUtf8(byte[] bytes) {

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java

@@ -17,6 +17,7 @@ import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.mailbox.MailboxModule;
 import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
+import org.briarproject.bramble.qrcode.QrCodeModule;
 import org.briarproject.bramble.record.RecordModule;
 import org.briarproject.bramble.reliability.ReliabilityModule;
 import org.briarproject.bramble.rendezvous.RendezvousModule;
@@ -47,6 +48,7 @@ import dagger.Module;
 		MailboxModule.class,
 		PluginModule.class,
 		PropertiesModule.class,
+		QrCodeModule.class,
 		RecordModule.class,
 		ReliabilityModule.class,
 		RendezvousModule.class,

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

@@ -19,7 +19,6 @@ import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
-import java.nio.charset.Charset;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
@@ -29,6 +28,7 @@ import javax.inject.Inject;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.api.crypto.DecryptionResult.INVALID_CIPHERTEXT;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.StringUtils.UTF_8;
 import static org.briarproject.bramble.util.StringUtils.fromHexString;
 import static org.briarproject.bramble.util.StringUtils.toHexString;
 
@@ -99,7 +99,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 		try {
 			BufferedReader reader = new BufferedReader(new InputStreamReader(
-					new FileInputStream(f), Charset.forName("UTF-8")));
+					new FileInputStream(f), UTF_8));
 			String key = reader.readLine();
 			reader.close();
 			return key;
@@ -151,7 +151,7 @@ class AccountManagerImpl implements AccountManager {
 	@GuardedBy("stateChangeLock")
 	private void writeDbKeyToFile(String key, File f) throws IOException {
 		FileOutputStream out = new FileOutputStream(f);
-		out.write(key.getBytes(Charset.forName("UTF-8")));
+		out.write(key.getBytes(UTF_8));
 		out.flush();
 		out.close();
 	}

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

@@ -29,7 +29,6 @@ import org.briarproject.nullsafety.NotNullByDefault;
 import org.whispersystems.curve25519.Curve25519;
 import org.whispersystems.curve25519.Curve25519KeyPair;
 
-import java.nio.charset.Charset;
 import java.security.GeneralSecurityException;
 import java.security.NoSuchAlgorithmException;
 import java.security.Provider;
@@ -51,6 +50,7 @@ import static org.briarproject.bramble.api.crypto.DecryptionResult.KEY_STRENGTHE
 import static org.briarproject.bramble.util.ByteUtils.INT_32_BYTES;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
+import static org.briarproject.bramble.util.StringUtils.US_ASCII;
 
 @NotNullByDefault
 class CryptoComponentImpl implements CryptoComponent {
@@ -460,7 +460,7 @@ class CryptoComponentImpl implements CryptoComponent {
 	@Override
 	public String encodeOnion(byte[] publicKey) {
 		Digest digest = new SHA3Digest(256);
-		byte[] label = ".onion checksum".getBytes(Charset.forName("US-ASCII"));
+		byte[] label = ".onion checksum".getBytes(US_ASCII);
 		digest.update(label, 0, label.length);
 		digest.update(publicKey, 0, publicKey.length);
 		digest.update(ONION_HS_PROTOCOL_VERSION);

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

@@ -39,12 +39,13 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.PrintStream;
-import java.nio.charset.Charset;
 import java.security.SecureRandom;
 import java.util.Scanner;
 
 import javax.annotation.concurrent.Immutable;
 
+import static org.briarproject.bramble.util.StringUtils.UTF_8;
+
 @Immutable
 @NotNullByDefault
 public class MessageEncrypter {
@@ -228,7 +229,7 @@ public class MessageEncrypter {
 		PublicKey publicKey =
 				encrypter.getKeyParser().parsePublicKey(keyBytes);
 		String message = readFully(System.in);
-		byte[] plaintext = message.getBytes(Charset.forName("UTF-8"));
+		byte[] plaintext = message.getBytes(UTF_8);
 		byte[] ciphertext = encrypter.encrypt(publicKey, plaintext);
 		System.out.println(AsciiArmour.wrap(ciphertext, LINE_LENGTH));
 	}
@@ -242,7 +243,7 @@ public class MessageEncrypter {
 				encrypter.getKeyParser().parsePrivateKey(keyBytes);
 		byte[] ciphertext = AsciiArmour.unwrap(readFully(System.in));
 		byte[] plaintext = encrypter.decrypt(privateKey, ciphertext);
-		System.out.println(new String(plaintext, Charset.forName("UTF-8")));
+		System.out.println(new String(plaintext, UTF_8));
 	}
 
 	private static String readFully(InputStream in) throws IOException {

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

@@ -1,7 +1,5 @@
 package org.briarproject.bramble.keyagreement;
 
-import org.briarproject.bramble.api.data.BdfReaderFactory;
-import org.briarproject.bramble.api.data.BdfWriterFactory;
 import org.briarproject.bramble.api.keyagreement.KeyAgreementTask;
 import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.api.keyagreement.PayloadParser;
@@ -19,13 +17,13 @@ public class KeyAgreementModule {
 	}
 
 	@Provides
-	PayloadEncoder providePayloadEncoder(BdfWriterFactory bdfWriterFactory) {
+	PayloadEncoder providePayloadEncoder(PayloadEncoderImpl payloadEncoder) {
-		return new PayloadEncoderImpl(bdfWriterFactory);
+		return payloadEncoder;
 	}
 
 	@Provides
-	PayloadParser providePayloadParser(BdfReaderFactory bdfReaderFactory) {
+	PayloadParser providePayloadParser(PayloadParserImpl payloadParser) {
-		return new PayloadParserImpl(bdfReaderFactory);
+		return payloadParser;
 	}
 
 	@Provides

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

@@ -13,7 +13,8 @@ import java.io.IOException;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.QR_FORMAT_ID;
+import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.QR_FORMAT_VERSION;
 
 @Immutable
 @NotNullByDefault
@@ -29,7 +30,8 @@ class PayloadEncoderImpl implements PayloadEncoder {
 	@Override
 	public byte[] encode(Payload p) {
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
-		out.write(PROTOCOL_VERSION);
+		int formatIdAndVersion = (QR_FORMAT_ID << 5) | QR_FORMAT_VERSION;
+		out.write(formatIdAndVersion);
 		BdfWriter w = bdfWriterFactory.createWriter(out);
 		try {
 			w.writeListStart(); // Payload start

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

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.keyagreement;
 
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.UnsupportedVersionException;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.data.BdfReader;
@@ -11,6 +12,9 @@ import org.briarproject.bramble.api.keyagreement.TransportDescriptor;
 import org.briarproject.bramble.api.plugin.BluetoothConstants;
 import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
+import org.briarproject.bramble.api.qrcode.WrongQrCodeTypeException;
 import org.briarproject.nullsafety.NotNullByDefault;
 
 import java.io.ByteArrayInputStream;
@@ -21,34 +25,42 @@ import java.util.List;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.BETA_PROTOCOL_VERSION;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.QR_FORMAT_VERSION;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_BLUETOOTH;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
 
 @Immutable
 @NotNullByDefault
 class PayloadParserImpl implements PayloadParser {
 
 	private final BdfReaderFactory bdfReaderFactory;
+	private final QrCodeClassifier qrCodeClassifier;
 
 	@Inject
-	PayloadParserImpl(BdfReaderFactory bdfReaderFactory) {
+	PayloadParserImpl(BdfReaderFactory bdfReaderFactory,
+			QrCodeClassifier qrCodeClassifier) {
 		this.bdfReaderFactory = bdfReaderFactory;
+		this.qrCodeClassifier = qrCodeClassifier;
 	}
 
 	@Override
-	public Payload parse(byte[] raw) throws IOException {
+	public Payload parse(String payloadString) throws IOException {
-		ByteArrayInputStream in = new ByteArrayInputStream(raw);
+		Pair<QrCodeType, Integer> typeAndVersion =
-		// First byte: the protocol version
+				qrCodeClassifier.classifyQrCode(payloadString);
-		int protocolVersion = in.read();
+		QrCodeType qrCodeType = typeAndVersion.getFirst();
-		if (protocolVersion == -1) throw new FormatException();
+		if (qrCodeType != BQP) throw new WrongQrCodeTypeException(qrCodeType);
-		if (protocolVersion != PROTOCOL_VERSION) {
+		int formatVersion = typeAndVersion.getSecond();
-			boolean tooOld = protocolVersion < PROTOCOL_VERSION ||
+		if (formatVersion != QR_FORMAT_VERSION) {
-					protocolVersion == BETA_PROTOCOL_VERSION;
+			boolean tooOld = formatVersion < QR_FORMAT_VERSION;
 			throw new UnsupportedVersionException(tooOld);
 		}
+		byte[] raw = payloadString.getBytes(ISO_8859_1);
+		ByteArrayInputStream in = new ByteArrayInputStream(raw);
+		// First byte: the format identifier and version (already parsed)
+		if (in.read() == -1) throw new AssertionError();
 		// The rest of the payload is a BDF list with one or more elements
 		BdfReader r = bdfReaderFactory.createReader(in);
 		BdfList payload = r.readList();

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxPairingTaskFactoryImpl.java

@@ -6,6 +6,7 @@ import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
 import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.nullsafety.NotNullByDefault;
 
@@ -25,6 +26,7 @@ class MailboxPairingTaskFactoryImpl implements MailboxPairingTaskFactory {
 	private final MailboxApi api;
 	private final MailboxSettingsManager mailboxSettingsManager;
 	private final MailboxUpdateManager mailboxUpdateManager;
+	private final QrCodeClassifier qrCodeClassifier;
 
 	@Inject
 	MailboxPairingTaskFactoryImpl(
@@ -34,7 +36,8 @@ class MailboxPairingTaskFactoryImpl implements MailboxPairingTaskFactory {
 			Clock clock,
 			MailboxApi api,
 			MailboxSettingsManager mailboxSettingsManager,
-			MailboxUpdateManager mailboxUpdateManager) {
+			MailboxUpdateManager mailboxUpdateManager,
+			QrCodeClassifier qrCodeClassifier) {
 		this.eventExecutor = eventExecutor;
 		this.db = db;
 		this.crypto = crypto;
@@ -42,12 +45,13 @@ class MailboxPairingTaskFactoryImpl implements MailboxPairingTaskFactory {
 		this.api = api;
 		this.mailboxSettingsManager = mailboxSettingsManager;
 		this.mailboxUpdateManager = mailboxUpdateManager;
+		this.qrCodeClassifier = qrCodeClassifier;
 	}
 
 	@Override
 	public MailboxPairingTask createPairingTask(String qrCodePayload) {
 		return new MailboxPairingTaskImpl(qrCodePayload, eventExecutor, db,
 				crypto, clock, api, mailboxSettingsManager,
-				mailboxUpdateManager);
+				mailboxUpdateManager, qrCodeClassifier);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxPairingTaskImpl.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.Consumer;
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseComponent;
@@ -9,18 +10,26 @@ import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
 import org.briarproject.bramble.api.mailbox.MailboxPairingState;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.ConnectionError;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.InvalidQrCode;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.MailboxAlreadyPaired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Paired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Pairing;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.QrCodeReceived;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.UnexpectedError;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
 import org.briarproject.bramble.api.mailbox.MailboxUpdate;
 import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
 import org.briarproject.bramble.mailbox.MailboxApi.MailboxAlreadyPairedException;
 import org.briarproject.nullsafety.NotNullByDefault;
 
 import java.io.IOException;
-import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -32,7 +41,10 @@ import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.QR_FORMAT_VERSION;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
 
 @ThreadSafe
 @NotNullByDefault
@@ -40,9 +52,6 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 
 	private final static Logger LOG =
 			getLogger(MailboxPairingTaskImpl.class.getName());
-	@SuppressWarnings("CharsetObjectCanBeUsed") // Requires minSdkVersion >= 19
-	private static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
-	private static final int VERSION_REQUIRED = 32;
 
 	private final String payload;
 	private final Executor eventExecutor;
@@ -52,6 +61,7 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 	private final MailboxApi api;
 	private final MailboxSettingsManager mailboxSettingsManager;
 	private final MailboxUpdateManager mailboxUpdateManager;
+	private final QrCodeClassifier qrCodeClassifier;
 	private final long timeStarted;
 
 	private final Object lock = new Object();
@@ -69,7 +79,8 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 			Clock clock,
 			MailboxApi api,
 			MailboxSettingsManager mailboxSettingsManager,
-			MailboxUpdateManager mailboxUpdateManager) {
+			MailboxUpdateManager mailboxUpdateManager,
+			QrCodeClassifier qrCodeClassifier) {
 		this.payload = payload;
 		this.eventExecutor = eventExecutor;
 		this.db = db;
@@ -78,8 +89,9 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 		this.api = api;
 		this.mailboxSettingsManager = mailboxSettingsManager;
 		this.mailboxUpdateManager = mailboxUpdateManager;
+		this.qrCodeClassifier = qrCodeClassifier;
 		timeStarted = clock.currentTimeMillis();
-		state = new MailboxPairingState.QrCodeReceived(timeStarted);
+		state = new QrCodeReceived(timeStarted);
 	}
 
 	@Override
@@ -101,22 +113,30 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 
 	@Override
 	public void run() {
+		Pair<QrCodeType, Integer> typeAndVersion =
+				qrCodeClassifier.classifyQrCode(payload);
+		QrCodeType qrCodeType = typeAndVersion.getFirst();
+		int formatVersion = typeAndVersion.getSecond();
+		if (qrCodeType != MAILBOX || formatVersion != QR_FORMAT_VERSION) {
+			setState(new InvalidQrCode(qrCodeType, formatVersion));
+			return;
+		}
 		try {
 			pairMailbox();
 		} catch (FormatException e) {
-			onMailboxError(e, new MailboxPairingState.InvalidQrCode());
+			onMailboxError(e, new InvalidQrCode(qrCodeType, formatVersion));
 		} catch (MailboxAlreadyPairedException e) {
-			onMailboxError(e, new MailboxPairingState.MailboxAlreadyPaired());
+			onMailboxError(e, new MailboxAlreadyPaired());
 		} catch (IOException e) {
-			onMailboxError(e, new MailboxPairingState.ConnectionError());
+			onMailboxError(e, new ConnectionError());
 		} catch (ApiException | DbException e) {
-			onMailboxError(e, new MailboxPairingState.UnexpectedError());
+			onMailboxError(e, new UnexpectedError());
 		}
 	}
 
 	private void pairMailbox() throws IOException, ApiException, DbException {
 		MailboxProperties mailboxProperties = decodeQrCodePayload(payload);
-		setState(new MailboxPairingState.Pairing(timeStarted));
+		setState(new Pairing(timeStarted));
 		MailboxProperties ownerProperties = api.setup(mailboxProperties);
 		long time = clock.currentTimeMillis();
 		db.transaction(false, txn -> {
@@ -135,7 +155,7 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 				}
 			}
 		});
-		setState(new MailboxPairingState.Paired());
+		setState(new Paired());
 	}
 
 	private void onMailboxError(Exception e, MailboxPairingState state) {
@@ -169,14 +189,6 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 			}
 			throw new FormatException();
 		}
-		int version = bytes[0] & 0xFF;
-		if (version != VERSION_REQUIRED) {
-			if (LOG.isLoggable(WARNING)) {
-				LOG.warning("QR code has not version " + VERSION_REQUIRED +
-						": " + version);
-			}
-			throw new FormatException();
-		}
 		LOG.info("QR code is valid");
 		byte[] onionPubKey = Arrays.copyOfRange(bytes, 1, 33);
 		String onion = crypto.encodeOnion(onionPubKey);

bramble-core/src/main/java/org/briarproject/bramble/plugin/tor/TorPlugin.java

@@ -46,7 +46,6 @@ import java.io.OutputStream;
 import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
-import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -100,6 +99,7 @@ import static org.briarproject.bramble.util.IoUtils.copyAndClose;
 import static org.briarproject.bramble.util.IoUtils.tryToClose;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubOnion;
+import static org.briarproject.bramble.util.StringUtils.UTF_8;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 @MethodsNotNullByDefault
@@ -419,9 +419,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		append(strb, "ClientTransportPlugin meek_lite exec", obfs4Path);
 		String snowflakePath = getSnowflakeExecutableFile().getAbsolutePath();
 		append(strb, "ClientTransportPlugin snowflake exec", snowflakePath);
-		//noinspection CharsetObjectCanBeUsed
+		return new ByteArrayInputStream(strb.toString().getBytes(UTF_8));
-		return new ByteArrayInputStream(
-				strb.toString().getBytes(Charset.forName("UTF-8")));
 	}
 
 	private void listFiles(File f) {

bramble-core/src/main/java/org/briarproject/bramble/plugin/tor/TorRendezvousCryptoImpl.java

@@ -7,7 +7,7 @@ import net.i2p.crypto.eddsa.spec.EdDSAPrivateKeySpec;
 import org.bouncycastle.util.encoders.Base64;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 
-import java.nio.charset.Charset;
+import static org.briarproject.bramble.util.StringUtils.US_ASCII;
 
 class TorRendezvousCryptoImpl implements TorRendezvousCrypto {
 
@@ -31,6 +31,6 @@ class TorRendezvousCryptoImpl implements TorRendezvousCrypto {
 		EdDSAPrivateKeySpec spec = new EdDSAPrivateKeySpec(seed, CURVE_SPEC);
 		byte[] hash = spec.getH();
 		byte[] base64 = Base64.encode(hash);
-		return "ED25519-V3:" + new String(base64, Charset.forName("US-ASCII"));
+		return "ED25519-V3:" + new String(base64, US_ASCII);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/qrcode/QrCodeClassifierImpl.java

@@ -0,0 +1,42 @@
+package org.briarproject.bramble.qrcode;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.keyagreement.KeyAgreementConstants;
+import org.briarproject.bramble.api.mailbox.MailboxConstants;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.UNKNOWN;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
+
+@Immutable
+@NotNullByDefault
+class QrCodeClassifierImpl implements QrCodeClassifier {
+
+	@Inject
+	QrCodeClassifierImpl() {
+	}
+
+	@Override
+	public Pair<QrCodeType, Integer> classifyQrCode(String payload) {
+		byte[] bytes = payload.getBytes(ISO_8859_1);
+		if (bytes.length == 0) return new Pair<>(UNKNOWN, 0);
+		// If this is a Bramble QR code then the first byte encodes the
+		// format ID (3 bits) and version (5 bits)
+		int formatIdAndVersion = bytes[0] & 0xFF;
+		int formatId = formatIdAndVersion >> 5;
+		int formatVersion = formatIdAndVersion & 0x1F;
+		if (formatId == KeyAgreementConstants.QR_FORMAT_ID) {
+			return new Pair<>(BQP, formatVersion);
+		}
+		if (formatId == MailboxConstants.QR_FORMAT_ID) {
+			return new Pair<>(MAILBOX, formatVersion);
+		}
+		return new Pair<>(UNKNOWN, 0);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/qrcode/QrCodeModule.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.qrcode;
+
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class QrCodeModule {
+
+	@Provides
+	QrCodeClassifier provideQrCodeClassifier(
+			QrCodeClassifierImpl qrCodeClassifier) {
+		return qrCodeClassifier;
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/account/AccountManagerImplTest.java

@@ -20,7 +20,6 @@ import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
-import java.nio.charset.Charset;
 
 import javax.annotation.Nullable;
 
@@ -34,6 +33,7 @@ import static org.briarproject.bramble.test.TestUtils.getIdentity;
 import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
 import static org.briarproject.bramble.test.TestUtils.getSecretKey;
 import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.briarproject.bramble.util.StringUtils.UTF_8;
 import static org.briarproject.bramble.util.StringUtils.getRandomString;
 import static org.briarproject.bramble.util.StringUtils.toHexString;
 import static org.junit.Assert.assertArrayEquals;
@@ -342,7 +342,7 @@ public class AccountManagerImplTest extends BrambleMockTestCase {
 	private void storeDatabaseKey(File f, String hex) throws IOException {
 		f.getParentFile().mkdirs();
 		FileOutputStream out = new FileOutputStream(f);
-		out.write(hex.getBytes(Charset.forName("UTF-8")));
+		out.write(hex.getBytes(UTF_8));
 		out.flush();
 		out.close();
 	}
@@ -350,7 +350,7 @@ public class AccountManagerImplTest extends BrambleMockTestCase {
 	@Nullable
 	private String loadDatabaseKey(File f) throws IOException {
 		BufferedReader reader = new BufferedReader(new InputStreamReader(
-				new FileInputStream(f), Charset.forName("UTF-8")));
+				new FileInputStream(f), UTF_8));
 		String hex = reader.readLine();
 		reader.close();
 		return hex;

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

@@ -2,21 +2,27 @@ package org.briarproject.bramble.keyagreement;
 
 import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.UnsupportedVersionException;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.data.BdfReader;
 import org.briarproject.bramble.api.data.BdfReaderFactory;
 import org.briarproject.bramble.api.keyagreement.Payload;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
+import org.briarproject.bramble.api.qrcode.WrongQrCodeTypeException;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.jmock.Expectations;
 import org.junit.Test;
 
 import java.io.ByteArrayInputStream;
 
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.BETA_PROTOCOL_VERSION;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.QR_FORMAT_VERSION;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
 import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
+import static org.briarproject.bramble.util.StringUtils.getRandomString;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -26,32 +32,29 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 
 	private final BdfReaderFactory bdfReaderFactory =
 			context.mock(BdfReaderFactory.class);
+	private final QrCodeClassifier qrCodeClassifier =
+			context.mock(QrCodeClassifier.class);
 	private final BdfReader bdfReader = context.mock(BdfReader.class);
 
-	private final PayloadParserImpl payloadParser =
+	private final String payload = getRandomString(123);
-			new PayloadParserImpl(bdfReaderFactory);
 
-	@Test(expected = FormatException.class)
+	private final PayloadParserImpl payloadParser =
-	public void testThrowsFormatExceptionIfPayloadIsEmpty() throws Exception {
+			new PayloadParserImpl(bdfReaderFactory, qrCodeClassifier);
-		payloadParser.parse(new byte[0]);
+
+	@Test(expected = WrongQrCodeTypeException.class)
+	public void testThrowsExceptionForWrongQrCodeType() throws Exception {
+		expectClassifyQrCode(payload, MAILBOX, QR_FORMAT_VERSION);
+
+		payloadParser.parse(payload);
 	}
 
 	@Test
 	public void testThrowsUnsupportedVersionExceptionForOldVersion()
 			throws Exception {
-		try {
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION - 1);
-			payloadParser.parse(new byte[] {PROTOCOL_VERSION - 1});
-			fail();
-		} catch (UnsupportedVersionException e) {
-			assertTrue(e.isTooOld());
-		}
-	}
 
-	@Test
-	public void testThrowsUnsupportedVersionExceptionForBetaVersion()
-			throws Exception {
 		try {
-			payloadParser.parse(new byte[] {BETA_PROTOCOL_VERSION});
+			payloadParser.parse(payload);
 			fail();
 		} catch (UnsupportedVersionException e) {
 			assertTrue(e.isTooOld());
@@ -61,8 +64,10 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 	@Test
 	public void testThrowsUnsupportedVersionExceptionForNewVersion()
 			throws Exception {
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION + 1);
+
 		try {
-			payloadParser.parse(new byte[] {PROTOCOL_VERSION + 1});
+			payloadParser.parse(payload);
 			fail();
 		} catch (UnsupportedVersionException e) {
 			assertFalse(e.isTooOld());
@@ -71,6 +76,8 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 
 	@Test(expected = FormatException.class)
 	public void testThrowsFormatExceptionForEmptyList() throws Exception {
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
+
 		context.checking(new Expectations() {{
 			oneOf(bdfReaderFactory).createReader(
 					with(any(ByteArrayInputStream.class)));
@@ -79,7 +86,7 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			will(returnValue(new BdfList()));
 		}});
 
-		payloadParser.parse(new byte[] {PROTOCOL_VERSION});
+		payloadParser.parse(payload);
 	}
 
 	@Test(expected = FormatException.class)
@@ -87,6 +94,8 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			throws Exception {
 		byte[] commitment = getRandomBytes(COMMIT_LENGTH);
 
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
+
 		context.checking(new Expectations() {{
 			oneOf(bdfReaderFactory).createReader(
 					with(any(ByteArrayInputStream.class)));
@@ -97,7 +106,7 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			will(returnValue(false));
 		}});
 
-		payloadParser.parse(new byte[] {PROTOCOL_VERSION});
+		payloadParser.parse(payload);
 	}
 
 	@Test(expected = FormatException.class)
@@ -105,6 +114,7 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			throws Exception {
 		byte[] commitment = getRandomBytes(COMMIT_LENGTH - 1);
 
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(bdfReaderFactory).createReader(
 					with(any(ByteArrayInputStream.class)));
@@ -115,7 +125,7 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			will(returnValue(true));
 		}});
 
-		payloadParser.parse(new byte[] {PROTOCOL_VERSION});
+		payloadParser.parse(payload);
 	}
 
 	@Test(expected = FormatException.class)
@@ -123,6 +133,7 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			throws Exception {
 		byte[] commitment = getRandomBytes(COMMIT_LENGTH + 1);
 
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(bdfReaderFactory).createReader(
 					with(any(ByteArrayInputStream.class)));
@@ -133,12 +144,14 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			will(returnValue(true));
 		}});
 
-		payloadParser.parse(new byte[] {PROTOCOL_VERSION});
+		payloadParser.parse(payload);
 	}
 
 	@Test
 	public void testAcceptsPayloadWithNoDescriptors() throws Exception {
 		byte[] commitment = getRandomBytes(COMMIT_LENGTH);
+
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(bdfReaderFactory).createReader(
 					with(any(ByteArrayInputStream.class)));
@@ -149,8 +162,16 @@ public class PayloadParserImplTest extends BrambleMockTestCase {
 			will(returnValue(true));
 		}});
 
-		Payload p = payloadParser.parse(new byte[] {PROTOCOL_VERSION});
+		Payload p = payloadParser.parse(payload);
 		assertArrayEquals(commitment, p.getCommitment());
 		assertTrue(p.getTransportDescriptors().isEmpty());
 	}
+
+	private void expectClassifyQrCode(String payload, QrCodeType qrCodeType,
+			int formatVersion) {
+		context.checking(new Expectations() {{
+			oneOf(qrCodeClassifier).classifyQrCode(payload);
+			will(returnValue(new Pair<>(qrCodeType, formatVersion)));
+		}});
+	}
 }

bramble-core/src/test/java/org/briarproject/bramble/mailbox/MailboxPairingTaskImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.mailbox;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseComponent;
@@ -7,13 +8,24 @@ import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
 import org.briarproject.bramble.api.mailbox.MailboxPairingState;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.ConnectionError;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.InvalidQrCode;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.MailboxAlreadyPaired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Paired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Pairing;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.QrCodeReceived;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.UnexpectedError;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
 import org.briarproject.bramble.api.mailbox.MailboxUpdate;
 import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
 import org.briarproject.bramble.api.mailbox.MailboxVersion;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
+import org.briarproject.bramble.mailbox.MailboxApi.MailboxAlreadyPairedException;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.test.ImmediateExecutor;
@@ -27,6 +39,9 @@ import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.util.Collections.singletonList;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.QR_FORMAT_VERSION;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
 import static org.briarproject.bramble.mailbox.MailboxTestUtils.getQrCodePayload;
 import static org.briarproject.bramble.test.TestUtils.getContact;
 import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
@@ -48,9 +63,8 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 			context.mock(MailboxSettingsManager.class);
 	private final MailboxUpdateManager mailboxUpdateManager =
 			context.mock(MailboxUpdateManager.class);
-	private final MailboxPairingTaskFactory factory =
+	private final QrCodeClassifier qrCodeClassifier =
-			new MailboxPairingTaskFactoryImpl(executor, db, crypto, clock, api,
+			context.mock(QrCodeClassifier.class);
-					mailboxSettingsManager, mailboxUpdateManager);
 
 	private final String onion = getRandomString(56);
 	private final byte[] onionBytes = getRandomBytes(32);
@@ -70,28 +84,48 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 	public void testInitialQrCodeReceivedState() {
 		MailboxPairingTask task = createPairingTask(getRandomString(42));
 		task.addObserver(state ->
-				assertTrue(state instanceof MailboxPairingState.QrCodeReceived)
+				assertTrue(state instanceof QrCodeReceived));
-		);
 	}
 
 	@Test
-	public void testInvalidQrCode() {
+	public void testInvalidQrCodeType() {
-		MailboxPairingTask task1 = createPairingTask(getRandomString(42));
+		String payload = getRandomString(65);
-		task1.run();
+		MailboxPairingTask task = createPairingTask(payload);
-		task1.addObserver(state ->
-				assertTrue(state instanceof MailboxPairingState.InvalidQrCode)
-		);
 
-		String goodLength = "00" + getRandomString(63);
+		expectClassifyQrCode(payload, BQP, QR_FORMAT_VERSION);
-		MailboxPairingTask task2 = createPairingTask(goodLength);
+
-		task2.run();
+		task.run();
-		task2.addObserver(state ->
+		task.addObserver(state ->
-				assertTrue(state instanceof MailboxPairingState.InvalidQrCode)
+				assertTrue(state instanceof InvalidQrCode));
-		);
+	}
+
+	@Test
+	public void testInvalidQrCodeVersion() {
+		String payload = getRandomString(65);
+		MailboxPairingTask task = createPairingTask(payload);
+
+		expectClassifyQrCode(payload, MAILBOX, QR_FORMAT_VERSION + 1);
+
+		task.run();
+		task.addObserver(state ->
+				assertTrue(state instanceof InvalidQrCode));
+	}
+
+	@Test
+	public void testInvalidQrCodeLength() {
+		String payload = getRandomString(42);
+		MailboxPairingTask task = createPairingTask(payload);
+
+		expectClassifyQrCode(payload, MAILBOX, QR_FORMAT_VERSION);
+
+		task.run();
+		task.addObserver(state ->
+				assertTrue(state instanceof InvalidQrCode));
 	}
 
 	@Test
 	public void testSuccessfulPairing() throws Exception {
+		expectClassifyQrCode(validPayload, MAILBOX, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(crypto).encodeOnion(onionBytes);
 			will(returnValue(onion));
@@ -122,14 +156,11 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 		MailboxPairingTask task = createPairingTask(validPayload);
 		task.addObserver(state -> {
 			if (i.get() == 0) {
-				assertEquals(MailboxPairingState.QrCodeReceived.class,
+				assertEquals(QrCodeReceived.class, state.getClass());
-						state.getClass());
 			} else if (i.get() == 1) {
-				assertEquals(MailboxPairingState.Pairing.class,
+				assertEquals(Pairing.class, state.getClass());
-						state.getClass());
 			} else if (i.get() == 2) {
-				assertEquals(MailboxPairingState.Paired.class,
+				assertEquals(Paired.class, state.getClass());
-						state.getClass());
 			} else fail("Unexpected change of state " + state.getClass());
 			i.getAndIncrement();
 		});
@@ -138,24 +169,23 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 
 	@Test
 	public void testAlreadyPaired() throws Exception {
-		testApiException(new MailboxApi.MailboxAlreadyPairedException(),
+		testApiException(new MailboxAlreadyPairedException(),
-				MailboxPairingState.MailboxAlreadyPaired.class);
+				MailboxAlreadyPaired.class);
 	}
 
 	@Test
 	public void testMailboxApiException() throws Exception {
-		testApiException(new MailboxApi.ApiException(),
+		testApiException(new ApiException(), UnexpectedError.class);
-				MailboxPairingState.UnexpectedError.class);
 	}
 
 	@Test
 	public void testApiIOException() throws Exception {
-		testApiException(new IOException(),
+		testApiException(new IOException(), ConnectionError.class);
-				MailboxPairingState.ConnectionError.class);
 	}
 
 	private void testApiException(Exception e,
 			Class<? extends MailboxPairingState> s) throws Exception {
+		expectClassifyQrCode(validPayload, MAILBOX, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(crypto).encodeOnion(onionBytes);
 			will(returnValue(onion));
@@ -170,6 +200,7 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 
 	@Test
 	public void testDbException() throws Exception {
+		expectClassifyQrCode(validPayload, MAILBOX, QR_FORMAT_VERSION);
 		context.checking(new Expectations() {{
 			oneOf(crypto).encodeOnion(onionBytes);
 			will(returnValue(onion));
@@ -188,8 +219,8 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 
 		MailboxPairingTask task = createPairingTask(validPayload);
 		task.run();
-		task.addObserver(state -> assertEquals(state.getClass(),
+		task.addObserver(state ->
-				MailboxPairingState.UnexpectedError.class));
+				assertEquals(state.getClass(), UnexpectedError.class));
 	}
 
 	private PredicateMatcher<MailboxProperties> matches(MailboxProperties p2) {
@@ -206,6 +237,16 @@ public class MailboxPairingTaskImplTest extends BrambleMockTestCase {
 			will(returnValue(time));
 		}});
 
-		return factory.createPairingTask(qrCodePayload);
+		return new MailboxPairingTaskImpl(qrCodePayload, executor, db,
+				crypto, clock, api, mailboxSettingsManager,
+				mailboxUpdateManager, qrCodeClassifier);
+	}
+
+	private void expectClassifyQrCode(String payload, QrCodeType qrCodeType,
+			int formatVersion) {
+		context.checking(new Expectations() {{
+			oneOf(qrCodeClassifier).classifyQrCode(payload);
+			will(returnValue(new Pair<>(qrCodeType, formatVersion)));
+		}});
 	}
 }

bramble-core/src/test/java/org/briarproject/bramble/mailbox/MailboxTestUtils.java

@@ -3,7 +3,6 @@ package org.briarproject.bramble.mailbox;
 import org.briarproject.bramble.api.WeakSingletonProvider;
 
 import java.nio.ByteBuffer;
-import java.nio.charset.Charset;
 
 import javax.annotation.Nonnull;
 import javax.net.SocketFactory;
@@ -11,20 +10,24 @@ import javax.net.SocketFactory;
 import okhttp3.OkHttpClient;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.QR_FORMAT_ID;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.QR_FORMAT_VERSION;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
 
 class MailboxTestUtils {
 
 	static String getQrCodePayload(byte[] onionBytes, byte[] setupToken) {
+		int formatIdAndVersion = (QR_FORMAT_ID << 5) | QR_FORMAT_VERSION;
 		byte[] payloadBytes = ByteBuffer.allocate(65)
-				.put((byte) 32) // 1
+				.put((byte) formatIdAndVersion) // 1
 				.put(onionBytes) // 32
 				.put(setupToken) // 32
 				.array();
-		//noinspection CharsetObjectCanBeUsed
+		return new String(payloadBytes, ISO_8859_1);
-		return new String(payloadBytes, Charset.forName("ISO-8859-1"));
 	}
 
+	// Used by mailbox integration tests
 	static String getQrCodePayload(byte[] setupToken) {
 		return getQrCodePayload(getRandomId(), setupToken);
 	}

bramble-core/src/test/java/org/briarproject/bramble/qrcode/QrCodeClassifierImplTest.java

@@ -0,0 +1,70 @@
+package org.briarproject.bramble.qrcode;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.keyagreement.KeyAgreementConstants;
+import org.briarproject.bramble.api.mailbox.MailboxConstants;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.junit.Test;
+
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.UNKNOWN;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
+import static org.junit.Assert.assertEquals;
+
+public class QrCodeClassifierImplTest extends BrambleTestCase {
+
+	private final QrCodeClassifier classifier = new QrCodeClassifierImpl();
+
+	@Test
+	public void testClassifiesEmptyStringAsUnknown() {
+		Pair<QrCodeType, Integer> result = classifier.classifyQrCode("");
+		assertEquals(UNKNOWN, result.getFirst());
+		assertEquals(0, result.getSecond().intValue());
+	}
+
+	@Test
+	public void testClassifiesKeyAgreement() {
+		byte[] payloadBytes = getRandomBytes(123);
+		for (int version = 0; version < 32; version++) {
+			int typeAndVersion =
+					(KeyAgreementConstants.QR_FORMAT_ID << 5) | version;
+			payloadBytes[0] = (byte) typeAndVersion;
+			String payload = new String(payloadBytes, ISO_8859_1);
+			Pair<QrCodeType, Integer> result =
+					classifier.classifyQrCode(payload);
+			assertEquals(BQP, result.getFirst());
+			assertEquals(version, result.getSecond().intValue());
+		}
+	}
+
+	@Test
+	public void testClassifiesMailbox() {
+		byte[] payloadBytes = getRandomBytes(123);
+		for (int version = 0; version < 32; version++) {
+			int typeAndVersion =
+					(MailboxConstants.QR_FORMAT_ID << 5) | version;
+			payloadBytes[0] = (byte) typeAndVersion;
+			String payload = new String(payloadBytes, ISO_8859_1);
+			Pair<QrCodeType, Integer> result =
+					classifier.classifyQrCode(payload);
+			assertEquals(MAILBOX, result.getFirst());
+			assertEquals(version, result.getSecond().intValue());
+		}
+	}
+
+	@Test
+	public void testClassifiesUnknownFormatIdAsUnknown() {
+		byte[] payloadBytes = getRandomBytes(123);
+		int unknownFormatId = MailboxConstants.QR_FORMAT_ID + 1;
+		int typeAndVersion = unknownFormatId << 5;
+		payloadBytes[0] = (byte) typeAndVersion;
+		String payload = new String(payloadBytes, ISO_8859_1);
+		Pair<QrCodeType, Integer> result = classifier.classifyQrCode(payload);
+		assertEquals(UNKNOWN, result.getFirst());
+		assertEquals(0, result.getSecond().intValue());
+	}
+}

bramble-java/src/main/java/org/briarproject/bramble/plugin/modem/ModemImpl.java

@@ -12,7 +12,6 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.charset.CharacterCodingException;
-import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Semaphore;
@@ -33,6 +32,7 @@ import static java.util.logging.Level.WARNING;
 import static jssc.SerialPort.PURGE_RXCLEAR;
 import static jssc.SerialPort.PURGE_TXCLEAR;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.StringUtils.US_ASCII;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -41,7 +41,6 @@ class ModemImpl implements Modem, WriteHandler, SerialPortEventListener {
 	private static final Logger LOG =
 			Logger.getLogger(ModemImpl.class.getName());
 
-	private static final Charset US_ASCII = Charset.forName("US-ASCII");
 	private static final int MAX_LINE_LENGTH = 256;
 	private static final int[] BAUD_RATES = {
 		256000, 128000, 115200, 57600, 38400, 19200, 14400, 9600, 4800, 1200

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

@@ -3,12 +3,14 @@ package org.briarproject.briar.android.contact.add.nearby;
 import android.graphics.Bitmap;
 
 import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
 
 import androidx.annotation.Nullable;
 
 abstract class AddContactState {
 
 	static class KeyAgreementListening extends AddContactState {
+
 		final Bitmap qrCode;
 
 		KeyAgreementListening(Bitmap qrCode) {
@@ -29,6 +31,7 @@ abstract class AddContactState {
 	}
 
 	static class ContactExchangeFinished extends AddContactState {
+
 		final ContactExchangeResult result;
 
 		ContactExchangeFinished(ContactExchangeResult result) {
@@ -37,25 +40,34 @@ abstract class AddContactState {
 	}
 
 	static class Failed extends AddContactState {
-		/**
-		 * Non-null if failed due to the scanned QR code version.
-		 * True if the app producing the code is too old.
-		 * False if the scanning app is too old.
-		 */
-		@Nullable
-		final Boolean qrCodeTooOld;
 
-		Failed(@Nullable Boolean qrCodeTooOld) {
+		static class WrongQrCodeType extends Failed {
-			this.qrCodeTooOld = qrCodeTooOld;
+
+			final QrCodeType qrCodeType;
+
+			WrongQrCodeType(QrCodeType qrCodeType) {
+				this.qrCodeType = qrCodeType;
+			}
 		}
 
-		Failed() {
+		static class WrongQrCodeVersion extends Failed {
-			this(null);
+
+			/**
+			 * True if the app producing the code is too old.
+			 * False if the scanning app is too old.
+			 */
+			final boolean qrCodeTooOld;
+
+			WrongQrCodeVersion(boolean qrCodeTooOld) {
+				this.qrCodeTooOld = qrCodeTooOld;
+			}
 		}
 	}
 
 	abstract static class ContactExchangeResult {
+
 		static class Success extends ContactExchangeResult {
+
 			final Author remoteAuthor;
 
 			Success(Author remoteAuthor) {
@@ -64,6 +76,7 @@ abstract class AddContactState {
 		}
 
 		static class Error extends ContactExchangeResult {
+
 			@Nullable
 			final Author duplicateAuthor;
 

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

@@ -6,12 +6,15 @@ import android.view.MenuItem;
 import android.widget.Toast;
 
 import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.ContactExchangeFinished;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.ContactExchangeResult;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed.WrongQrCodeType;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed.WrongQrCodeVersion;
 import org.briarproject.briar.android.contact.add.nearby.AddNearbyContactViewModel.BluetoothDecision;
 import org.briarproject.briar.android.fragment.BaseFragment;
 import org.briarproject.briar.android.fragment.BaseFragment.BaseFragmentListener;
@@ -34,6 +37,7 @@ import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.widget.Toast.LENGTH_LONG;
 import static java.util.Objects.requireNonNull;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
 import static org.briarproject.briar.android.contact.add.nearby.AddNearbyContactViewModel.BluetoothDecision.ACCEPTED;
 import static org.briarproject.briar.android.contact.add.nearby.AddNearbyContactViewModel.BluetoothDecision.REFUSED;
 
@@ -141,9 +145,15 @@ public class AddNearbyContactActivity extends BriarActivity
 			ContactExchangeResult result =
 					((ContactExchangeFinished) state).result;
 			onContactExchangeResult(result);
+		} else if (state instanceof WrongQrCodeType) {
+			QrCodeType qrCodeType = ((WrongQrCodeType) state).qrCodeType;
+			if (qrCodeType == MAILBOX) onMailboxQrCodeScanned();
+			else onWrongQrCodeType();
+		} else if (state instanceof WrongQrCodeVersion) {
+			boolean qrCodeTooOld = ((WrongQrCodeVersion) state).qrCodeTooOld;
+			onWrongQrCodeVersion(qrCodeTooOld);
 		} else if (state instanceof Failed) {
-			Boolean qrCodeTooOld = ((Failed) state).qrCodeTooOld;
+			showErrorFragment();
-			onAddingContactFailed(qrCodeTooOld);
 		}
 	}
 
@@ -170,15 +180,27 @@ public class AddNearbyContactActivity extends BriarActivity
 		} else throw new AssertionError();
 	}
 
-	private void onAddingContactFailed(@Nullable Boolean qrCodeTooOld) {
+	private void onMailboxQrCodeScanned() {
-		if (qrCodeTooOld == null) {
+		String title = getString(R.string.qr_code_invalid);
-			showErrorFragment();
+		String msg = getString(R.string.mailbox_qr_code_for_contact);
-		} else {
+		showNextFragment(
-			String msg;
+				AddNearbyContactErrorFragment.newInstance(title, msg, false));
-			if (qrCodeTooOld) msg = getString(R.string.qr_code_too_old_1);
+	}
-			else msg = getString(R.string.qr_code_too_new_1);
+
-			showNextFragment(AddNearbyContactErrorFragment.newInstance(msg));
+	private void onWrongQrCodeType() {
-		}
+		String title = getString(R.string.qr_code_invalid);
+		String msg = getString(R.string.qr_code_format_unknown);
+		showNextFragment(
+				AddNearbyContactErrorFragment.newInstance(title, msg, false));
+	}
+
+	private void onWrongQrCodeVersion(boolean qrCodeTooOld) {
+		String title = getString(R.string.qr_code_invalid);
+		String msg;
+		if (qrCodeTooOld) msg = getString(R.string.qr_code_too_old_1);
+		else msg = getString(R.string.qr_code_too_new_1);
+		showNextFragment(
+				AddNearbyContactErrorFragment.newInstance(title, msg, false));
 	}
 
 	private void showErrorFragment() {

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

@@ -22,6 +22,7 @@ import androidx.fragment.app.FragmentActivity;
 import androidx.lifecycle.ViewModelProvider;
 
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
+import static android.view.View.GONE;
 import static org.briarproject.briar.android.util.UiUtils.hideViewOnSmallScreen;
 import static org.briarproject.briar.android.util.UiUtils.onSingleLinkClick;
 
@@ -31,17 +32,22 @@ public class AddNearbyContactErrorFragment extends BaseFragment {
 
 	public static final String TAG =
 			AddNearbyContactErrorFragment.class.getName();
-	private static final String ERROR_MSG = "errorMessage";
+	private static final String ARG_TITLE = "title";
+	private static final String ARG_ERROR_MSG = "message";
+	private static final String ARG_FEEDBACK = "feedback";
 
 	@Inject
 	ViewModelProvider.Factory viewModelFactory;
 
 	private AddNearbyContactViewModel viewModel;
 
-	public static AddNearbyContactErrorFragment newInstance(String errorMsg) {
+	public static AddNearbyContactErrorFragment newInstance(String title,
+			String errorMessage, boolean feedback) {
 		AddNearbyContactErrorFragment f = new AddNearbyContactErrorFragment();
 		Bundle args = new Bundle();
-		args.putString(ERROR_MSG, errorMsg);
+		args.putString(ARG_TITLE, title);
+		args.putString(ARG_ERROR_MSG, errorMessage);
+		args.putBoolean(ARG_FEEDBACK, feedback);
 		f.setArguments(args);
 		return f;
 	}
@@ -66,19 +72,32 @@ public class AddNearbyContactErrorFragment extends BaseFragment {
 		View v = inflater.inflate(R.layout.fragment_error_contact_exchange,
 				container, false);
 
-		// set optional error message
+		String title = null, errorMessage = null;
-		TextView explanation = v.findViewById(R.id.errorMessage);
+		boolean feedback = true;
 		Bundle args = getArguments();
-		String errorMessage = args == null ? null : args.getString(ERROR_MSG);
+		if (args != null) {
-		if (errorMessage == null) {
+			title = args.getString(ARG_TITLE);
-			explanation.setText(getString(R.string.add_contact_error_two_way));
+			errorMessage = args.getString(ARG_ERROR_MSG);
-		} else {
+			feedback = args.getBoolean(ARG_FEEDBACK, true);
-			explanation.setText(args.getString(ERROR_MSG));
+		}
+
+		if (title != null) {
+			TextView titleView = v.findViewById(R.id.errorTitle);
+			titleView.setText(title);
+		}
+
+		if (errorMessage != null) {
+			TextView messageView = v.findViewById(R.id.errorMessage);
+			messageView.setText(errorMessage);
 		}
 
-		// make feedback link clickable
 		TextView sendFeedback = v.findViewById(R.id.sendFeedback);
-		onSingleLinkClick(sendFeedback, this::triggerFeedback);
+		if (feedback) {
+			// make feedback link clickable
+			onSingleLinkClick(sendFeedback, this::triggerFeedback);
+		} else {
+			sendFeedback.setVisibility(GONE);
+		}
 
 		// buttons
 		Button tryAgain = v.findViewById(R.id.tryAgainButton);

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

@@ -43,6 +43,7 @@ import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.plugin.event.TransportStateEvent;
+import org.briarproject.bramble.api.qrcode.WrongQrCodeTypeException;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.plugin.bluetooth.BluetoothPlugin;
 import org.briarproject.briar.R;
@@ -50,9 +51,13 @@ import org.briarproject.briar.android.contact.add.nearby.AddContactState.Contact
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.ContactExchangeResult.Error;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.ContactExchangeResult.Success;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.ContactExchangeStarted;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed.WrongQrCodeType;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.Failed.WrongQrCodeVersion;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementListening;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementStarted;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementWaiting;
+import org.briarproject.briar.android.contact.add.nearby.AddContactState.QrCodeScanned;
 import org.briarproject.briar.android.qrcode.QrCodeDecoder;
 import org.briarproject.briar.android.qrcode.QrCodeUtils;
 import org.briarproject.briar.android.viewmodel.LiveEvent;
@@ -60,7 +65,6 @@ import org.briarproject.briar.android.viewmodel.MutableLiveEvent;
 import org.briarproject.nullsafety.NotNullByDefault;
 
 import java.io.IOException;
-import java.nio.charset.Charset;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
@@ -85,6 +89,7 @@ import static org.briarproject.bramble.api.plugin.Plugin.State.DISABLED;
 import static org.briarproject.bramble.api.plugin.Plugin.State.INACTIVE;
 import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.StringUtils.ISO_8859_1;
 import static org.briarproject.briar.android.contact.add.nearby.AddNearbyContactPermissionManager.areEssentialPermissionsGranted;
 import static org.briarproject.briar.android.contact.add.nearby.AddNearbyContactViewModel.BluetoothDecision.NO_ADAPTER;
 import static org.briarproject.briar.android.contact.add.nearby.AddNearbyContactViewModel.BluetoothDecision.REFUSED;
@@ -126,9 +131,6 @@ class AddNearbyContactViewModel extends AndroidViewModel
 		REFUSED
 	}
 
-	@SuppressWarnings("CharsetObjectCanBeUsed") // Requires minSdkVersion >= 19
-	private static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
-
 	private final EventBus eventBus;
 	private final AndroidExecutor androidExecutor;
 	private final Executor ioExecutor;
@@ -376,11 +378,11 @@ class AddNearbyContactViewModel extends AndroidViewModel
 		} else if (e instanceof KeyAgreementAbortedEvent) {
 			LOG.info("KeyAgreementAbortedEvent received");
 			resetPayloadFlags();
-			state.setValue(new AddContactState.Failed());
+			state.setValue(new Failed());
 		} else if (e instanceof KeyAgreementFailedEvent) {
 			LOG.info("KeyAgreementFailedEvent received");
 			resetPayloadFlags();
-			state.setValue(new AddContactState.Failed());
+			state.setValue(new Failed());
 		}
 	}
 
@@ -446,22 +448,22 @@ class AddNearbyContactViewModel extends AndroidViewModel
 		// Ignore results until the KeyAgreementTask is ready
 		if (!gotLocalPayload || gotRemotePayload || currentTask == null) return;
 		try {
-			byte[] payloadBytes = result.getText().getBytes(ISO_8859_1);
+			Payload remotePayload = payloadParser.parse(result.getText());
-			if (LOG.isLoggable(INFO))
-				LOG.info("Remote payload is " + payloadBytes.length + " bytes");
-			Payload remotePayload = payloadParser.parse(payloadBytes);
 			gotRemotePayload = true;
 			currentTask.connectAndRunProtocol(remotePayload);
-			state.postValue(new AddContactState.QrCodeScanned());
+			state.postValue(new QrCodeScanned());
+		} catch (WrongQrCodeTypeException e) {
+			resetPayloadFlags();
+			state.postValue(new WrongQrCodeType(e.getQrCodeType()));
 		} catch (UnsupportedVersionException e) {
 			resetPayloadFlags();
-			state.postValue(new AddContactState.Failed(e.isTooOld()));
+			state.postValue(new WrongQrCodeVersion(e.isTooOld()));
 		} catch (IOException | IllegalArgumentException e) {
 			LOG.log(WARNING, "QR Code Invalid", e);
 			androidExecutor.runOnUiThread(() -> Toast.makeText(getApplication(),
 					R.string.qr_code_invalid, LENGTH_LONG).show());
 			resetPayloadFlags();
-			state.postValue(new AddContactState.Failed());
+			state.postValue(new Failed());
 		}
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotManager.java

@@ -436,7 +436,7 @@ class HotspotManager {
 	}
 
 	private static String createWifiLoginString(String ssid, String password) {
-		// https://en.wikipedia.org/wiki/QR_code#WiFi_network_login
+		// https://en.wikipedia.org/wiki/QR_code#Joining_a_Wi%E2%80%91Fi_network
 		// do not remove the dangling ';', it can cause problems to omit it
 		return "WIFI:S:" + ssid + ";T:WPA;P:" + password + ";;";
 	}

briar-android/src/main/java/org/briarproject/briar/android/mailbox/MailboxActivity.java

@@ -6,10 +6,24 @@ import android.widget.ProgressBar;
 import android.widget.Toast;
 
 import org.briarproject.bramble.api.mailbox.MailboxPairingState;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.ConnectionError;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.InvalidQrCode;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.MailboxAlreadyPaired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Paired;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Pending;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.UnexpectedError;
 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.FinalFragment;
+import org.briarproject.briar.android.mailbox.MailboxState.CameraError;
+import org.briarproject.briar.android.mailbox.MailboxState.IsPaired;
+import org.briarproject.briar.android.mailbox.MailboxState.NotSetup;
+import org.briarproject.briar.android.mailbox.MailboxState.OfflineWhenPairing;
+import org.briarproject.briar.android.mailbox.MailboxState.Pairing;
+import org.briarproject.briar.android.mailbox.MailboxState.ScanningQrCode;
+import org.briarproject.briar.android.mailbox.MailboxState.ShowDownload;
+import org.briarproject.briar.android.mailbox.MailboxState.WasUnpaired;
 import org.briarproject.briar.android.view.BlankFragment;
 import org.briarproject.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.nullsafety.ParametersNotNullByDefault;
@@ -25,6 +39,9 @@ import androidx.lifecycle.ViewModelProvider;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
 import static android.widget.Toast.LENGTH_LONG;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.QR_FORMAT_VERSION;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.BQP;
+import static org.briarproject.bramble.api.qrcode.QrCodeClassifier.QrCodeType.MAILBOX;
 import static org.briarproject.briar.android.util.UiUtils.showFragment;
 
 @MethodsNotNullByDefault
@@ -56,24 +73,23 @@ public class MailboxActivity extends BriarActivity {
 		}
 
 		viewModel.getPairingState().observeEvent(this, state -> {
-			if (state instanceof MailboxState.NotSetup) {
+			if (state instanceof NotSetup) {
 				onNotSetup();
-			} else if (state instanceof MailboxState.ShowDownload) {
+			} else if (state instanceof ShowDownload) {
 				onShowDownload();
-			} else if (state instanceof MailboxState.ScanningQrCode) {
+			} else if (state instanceof ScanningQrCode) {
 				onScanningQrCode();
-			} else if (state instanceof MailboxState.Pairing) {
+			} else if (state instanceof Pairing) {
-				MailboxPairingState s =
+				MailboxPairingState s = ((Pairing) state).pairingState;
-						((MailboxState.Pairing) state).pairingState;
 				onMailboxPairingStateChanged(s);
-			} else if (state instanceof MailboxState.OfflineWhenPairing) {
+			} else if (state instanceof OfflineWhenPairing) {
 				onOffline();
-			} else if (state instanceof MailboxState.CameraError) {
+			} else if (state instanceof CameraError) {
 				onCameraError();
-			} else if (state instanceof MailboxState.IsPaired) {
+			} else if (state instanceof IsPaired) {
-				onIsPaired(((MailboxState.IsPaired) state).isOnline);
+				onIsPaired(((IsPaired) state).isOnline);
-			} else if (state instanceof MailboxState.WasUnpaired) {
+			} else if (state instanceof WasUnpaired) {
-				MailboxState.WasUnpaired s = (MailboxState.WasUnpaired) state;
+				WasUnpaired s = (WasUnpaired) state;
 				onUnPaired(s.tellUserToWipeMailbox);
 			} else {
 				throw new AssertionError("Unknown state: " + state);
@@ -104,7 +120,7 @@ public class MailboxActivity extends BriarActivity {
 	@Override
 	public void onBackPressed() {
 		MailboxState s = viewModel.getPairingState().getLastValue();
-		if (s instanceof MailboxState.Pairing) {
+		if (s instanceof Pairing) {
 			// don't go back in the flow if we are already pairing
 			// with the mailbox. We provide a try-again button instead.
 			supportFinishAfterTransition();
@@ -158,31 +174,44 @@ public class MailboxActivity extends BriarActivity {
 		}
 		Fragment f;
 		String tag;
-		if (s instanceof MailboxPairingState.Pending) {
+		if (s instanceof Pending) {
-			long timeStarted = ((MailboxPairingState.Pending) s).timeStarted;
+			long timeStarted = ((Pending) s).timeStarted;
 			f = MailboxConnectingFragment.newInstance(timeStarted);
 			tag = MailboxConnectingFragment.TAG;
-		} else if (s instanceof MailboxPairingState.InvalidQrCode) {
+		} else if (s instanceof InvalidQrCode) {
-			f = ErrorFragment.newInstance(
+			InvalidQrCode i = (InvalidQrCode) s;
-					R.string.mailbox_setup_qr_code_wrong_title,
+			int errorRes;
-					R.string.mailbox_setup_qr_code_wrong_description);
+			if (i.qrCodeType == MAILBOX) {
+				if (i.formatVersion < QR_FORMAT_VERSION) {
+					errorRes = R.string.mailbox_qr_code_too_old;
+				} else if (i.formatVersion > QR_FORMAT_VERSION) {
+					errorRes = R.string.mailbox_qr_code_too_new;
+				} else {
+					errorRes = R.string.mailbox_setup_qr_code_wrong_description;
+				}
+			} else if (i.qrCodeType == BQP) {
+				errorRes = R.string.contact_qr_code_for_mailbox;
+			} else {
+				errorRes = R.string.mailbox_setup_qr_code_wrong_description;
+			}
+			f = ErrorFragment.newInstance(R.string.qr_code_invalid, errorRes);
 			tag = ErrorFragment.TAG;
-		} else if (s instanceof MailboxPairingState.MailboxAlreadyPaired) {
+		} else if (s instanceof MailboxAlreadyPaired) {
 			f = ErrorFragment.newInstance(
 					R.string.mailbox_setup_already_paired_title,
 					R.string.mailbox_setup_already_paired_description);
 			tag = ErrorFragment.TAG;
-		} else if (s instanceof MailboxPairingState.ConnectionError) {
+		} else if (s instanceof ConnectionError) {
 			f = ErrorFragment.newInstance(
 					R.string.mailbox_setup_io_error_title,
 					R.string.mailbox_setup_io_error_description);
 			tag = ErrorFragment.TAG;
-		} else if (s instanceof MailboxPairingState.UnexpectedError) {
+		} else if (s instanceof UnexpectedError) {
 			f = ErrorFragment.newInstance(
 					R.string.mailbox_setup_assertion_error_title,
 					R.string.mailbox_setup_assertion_error_description);
 			tag = ErrorFragment.TAG;
-		} else if (s instanceof MailboxPairingState.Paired) {
+		} else if (s instanceof Paired) {
 			f = FinalFragment.newInstance(R.string.mailbox_setup_paired_title,
 					R.drawable.ic_check_circle_outline,
 					R.color.briar_brand_green,

briar-android/src/main/java/org/briarproject/briar/android/mailbox/MailboxViewModel.java

@@ -15,6 +15,7 @@ import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.mailbox.MailboxManager;
 import org.briarproject.bramble.api.mailbox.MailboxPairingState;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Paired;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxStatus;
 import org.briarproject.bramble.api.mailbox.event.OwnMailboxConnectionStatusEvent;
@@ -24,7 +25,14 @@ import org.briarproject.bramble.api.plugin.TorConstants;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.briar.android.mailbox.MailboxState.CameraError;
+import org.briarproject.briar.android.mailbox.MailboxState.IsPaired;
 import org.briarproject.briar.android.mailbox.MailboxState.NotSetup;
+import org.briarproject.briar.android.mailbox.MailboxState.OfflineWhenPairing;
+import org.briarproject.briar.android.mailbox.MailboxState.Pairing;
+import org.briarproject.briar.android.mailbox.MailboxState.ScanningQrCode;
+import org.briarproject.briar.android.mailbox.MailboxState.ShowDownload;
+import org.briarproject.briar.android.mailbox.MailboxState.WasUnpaired;
 import org.briarproject.briar.android.qrcode.QrCodeDecoder;
 import org.briarproject.briar.android.viewmodel.DbViewModel;
 import org.briarproject.briar.android.viewmodel.LiveEvent;
@@ -113,7 +121,7 @@ class MailboxViewModel extends DbViewModel
 					MailboxStatus mailboxStatus =
 							mailboxManager.getMailboxStatus(txn);
 					boolean isOnline = isTorActive();
-					pairingState.postEvent(new MailboxState.IsPaired(isOnline));
+					pairingState.postEvent(new IsPaired(isOnline));
 					status.postValue(mailboxStatus);
 				} else {
 					pairingState.postEvent(new NotSetup());
@@ -142,14 +150,14 @@ class MailboxViewModel extends DbViewModel
 	@UiThread
 	private void onTorInactive() {
 		MailboxState lastState = pairingState.getLastValue();
-		if (lastState instanceof MailboxState.IsPaired) {
+		if (lastState instanceof IsPaired) {
 			// we are already paired, so use IsPaired state
-			pairingState.setEvent(new MailboxState.IsPaired(false));
+			pairingState.setEvent(new IsPaired(false));
-		} else if (lastState instanceof MailboxState.Pairing) {
+		} else if (lastState instanceof Pairing) {
-			MailboxState.Pairing p = (MailboxState.Pairing) lastState;
+			Pairing p = (Pairing) lastState;
 			// check that we not just finished pairing (showing success screen)
-			if (!(p.pairingState instanceof MailboxPairingState.Paired)) {
+			if (!(p.pairingState instanceof Paired)) {
-				pairingState.setEvent(new MailboxState.OfflineWhenPairing());
+				pairingState.setEvent(new OfflineWhenPairing());
 			}
 			// else ignore offline event as user will be leaving UI flow anyway
 		}
@@ -158,15 +166,15 @@ class MailboxViewModel extends DbViewModel
 	@UiThread
 	void onScanButtonClicked() {
 		if (isTorActive()) {
-			pairingState.setEvent(new MailboxState.ScanningQrCode());
+			pairingState.setEvent(new ScanningQrCode());
 		} else {
-			pairingState.setEvent(new MailboxState.OfflineWhenPairing());
+			pairingState.setEvent(new OfflineWhenPairing());
 		}
 	}
 
 	@UiThread
 	void onCameraError() {
-		pairingState.setEvent(new MailboxState.CameraError());
+		pairingState.setEvent(new CameraError());
 	}
 
 	@Override
@@ -182,7 +190,7 @@ class MailboxViewModel extends DbViewModel
 			pairingTask = mailboxManager.startPairingTask(qrCodePayload);
 			pairingTask.addObserver(this);
 		} else {
-			pairingState.postEvent(new MailboxState.OfflineWhenPairing());
+			pairingState.postEvent(new OfflineWhenPairing());
 		}
 	}
 
@@ -193,7 +201,7 @@ class MailboxViewModel extends DbViewModel
 			LOG.info("New pairing state: " +
 					mailboxPairingState.getClass().getSimpleName());
 		}
-		pairingState.setEvent(new MailboxState.Pairing(mailboxPairingState));
+		pairingState.setEvent(new Pairing(mailboxPairingState));
 	}
 
 	private boolean isTorActive() {
@@ -203,7 +211,7 @@ class MailboxViewModel extends DbViewModel
 
 	@UiThread
 	void showDownloadFragment() {
-		pairingState.setEvent(new MailboxState.ShowDownload());
+		pairingState.setEvent(new ShowDownload());
 	}
 
 	@UiThread
@@ -214,7 +222,7 @@ class MailboxViewModel extends DbViewModel
 	@UiThread
 	void checkIfOnlineWhenPaired() {
 		boolean isOnline = isTorActive();
-		pairingState.setEvent(new MailboxState.IsPaired(isOnline));
+		pairingState.setEvent(new IsPaired(isOnline));
 	}
 
 	LiveData<Boolean> checkConnection() {
@@ -227,7 +235,7 @@ class MailboxViewModel extends DbViewModel
 		checkConnection(success -> {
 			boolean isOnline = isTorActive();
 			// make UI move back to status fragment by changing pairingState
-			pairingState.postEvent(new MailboxState.IsPaired(isOnline));
+			pairingState.postEvent(new IsPaired(isOnline));
 		});
 	}
 
@@ -246,7 +254,7 @@ class MailboxViewModel extends DbViewModel
 		ioExecutor.execute(() -> {
 			try {
 				boolean wasWiped = mailboxManager.unPair();
-				pairingState.postEvent(new MailboxState.WasUnpaired(!wasWiped));
+				pairingState.postEvent(new WasUnpaired(!wasWiped));
 			} catch (DbException e) {
 				handleException(e);
 			}

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

@@ -41,7 +41,6 @@ public class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	private final ResultCallback callback;
 
 	private Camera camera = null;
-	private int cameraIndex = 0;
 
 	public QrCodeDecoder(AndroidExecutor androidExecutor,
 			@IoExecutor Executor ioExecutor, ResultCallback callback) {
@@ -53,14 +52,12 @@ public class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
 	@Override
 	public void start(Camera camera, int cameraIndex) {
 		this.camera = camera;
-		this.cameraIndex = cameraIndex;
 		askForPreviewFrame();
 	}
 
 	@Override
 	public void stop() {
 		camera = null;
-		cameraIndex = 0;
 	}
 
 	@UiThread

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

@@ -51,12 +51,12 @@
 				android:layout_width="0dp"
 				android:layout_height="wrap_content"
 				android:layout_marginTop="@dimen/margin_xlarge"
+				android:text="@string/add_contact_error_two_way"
 				android:textAppearance="@style/TextAppearance.MaterialComponents.Body1"
 				app:layout_constraintBottom_toTopOf="@+id/sendFeedback"
 				app:layout_constraintEnd_toEndOf="parent"
 				app:layout_constraintStart_toStartOf="parent"
-				app:layout_constraintTop_toBottomOf="@+id/errorTitle"
+				app:layout_constraintTop_toBottomOf="@+id/errorTitle" />
-				tools:text="error explanation" />
 
 			<TextView
 				android:id="@+id/sendFeedback"

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

@@ -252,6 +252,8 @@
 	<string name="qr_code_invalid">The QR code is invalid</string>
 	<string name="qr_code_too_old_1">The QR code you have scanned comes from an older version of Briar.\n\nPlease ask your contact to upgrade to the latest version and then try again.</string>
 	<string name="qr_code_too_new_1">The QR code you have scanned comes from a newer version of Briar.\n\nPlease upgrade to the latest version and then try again.</string>
+	<string name="mailbox_qr_code_for_contact">The QR code you have scanned comes from Briar Mailbox.\n\nIf you want to link a Mailbox, please choose Settings > Mailbox from the Briar menu.</string>
+	<string name="qr_code_format_unknown">The QR code you have scanned does not come from Briar.\n\nPlease scan the QR code shown on your contact\'s screen.</string>
 	<string name="camera_error">Camera error</string>
 	<string name="connecting_to_device">Connecting to device\u2026</string>
 	<string name="authenticating_with_device">Authenticating with device\u2026</string>
@@ -636,8 +638,10 @@
 	<string name="mailbox_setup_connecting">Connecting to Mailbox…</string>
 	<!-- This string is shown when connecting to a Mailbox for the first time. The placeholder will be replaced with a duration, e.g. "2 minutes". -->
 	<string name="mailbox_setup_connecting_info">This may take up to %1s</string>
-	<string name="mailbox_setup_qr_code_wrong_title">Wrong QR code</string>
+	<string name="mailbox_qr_code_too_old">The QR code you have scanned comes from an older version of Briar Mailbox.\n\nPlease upgrade Briar Mailbox to the latest version and then try again.</string>
-	<string name="mailbox_setup_qr_code_wrong_description">The scanned code is invalid. Please open the Briar Mailbox app on your Mailbox device and scan the QR code it presents.</string>
+	<string name="mailbox_qr_code_too_new">The QR code you have scanned comes from a newer version of Briar Mailbox.\n\nPlease upgrade Briar to the latest version and then try again.</string>
+	<string name="contact_qr_code_for_mailbox">The QR code you have scanned is for adding a Briar contact.\n\nIf you want to add a contact, please go to the contact list and tap the + icon.</string>
+	<string name="mailbox_setup_qr_code_wrong_description">The QR code you have scanned does not come from Briar Mailbox.\n\nPlease open the Briar Mailbox app on your Mailbox device and scan the QR code it presents.</string>
 	<string name="mailbox_setup_already_paired_title">Mailbox already linked</string>
 	<string name="mailbox_setup_already_paired_description">Unlink the Mailbox on your other device and try again.</string>
 	<string name="mailbox_setup_io_error_title">Could not connect</string>

mailbox-integration-tests/src/test/java/org/briarproject/bramble/mailbox/AbstractMailboxIntegrationTest.java

@@ -11,7 +11,7 @@ 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.mailbox.MailboxAuthToken;
-import org.briarproject.bramble.api.mailbox.MailboxPairingState;
+import org.briarproject.bramble.api.mailbox.MailboxPairingState.Paired;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxUpdateWithMailbox;
@@ -121,7 +121,7 @@ abstract class AbstractMailboxIntegrationTest
 
 		CountDownLatch latch = new CountDownLatch(1);
 		pairingTask.addObserver((state) -> {
-			if (state instanceof MailboxPairingState.Paired) {
+			if (state instanceof Paired) {
 				latch.countDown();
 			}
 		});