1 files changed, 228 insertions, 0 deletions
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java
new file mode 100644
index 00000000..566835d6
--- /dev/null
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java
@@ -0,0 +1,228 @@
+package eu.siacs.conversations.crypto.sasl;
+
+import android.annotation.TargetApi;
+import android.os.Build;
+import android.util.Base64;
+import android.util.LruCache;
+
+import org.bouncycastle.crypto.Digest;
+import org.bouncycastle.crypto.macs.HMac;
+import org.bouncycastle.crypto.params.KeyParameter;
+
+import java.math.BigInteger;
+import java.nio.charset.Charset;
+import java.security.InvalidKeyException;
+import java.security.SecureRandom;
+
+import eu.siacs.conversations.entities.Account;
+import eu.siacs.conversations.utils.CryptoHelper;
+import eu.siacs.conversations.xml.TagWriter;
+
+@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
+abstract class ScramMechanism extends SaslMechanism {
+	// TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to indicate support and/or usage.
+	private final static String GS2_HEADER = "n,,";
+	private String clientFirstMessageBare;
+	private final String clientNonce;
+	private byte[] serverSignature = null;
+	static HMac HMAC;
+	static Digest DIGEST;
+	private static final byte[] CLIENT_KEY_BYTES = "Client Key".getBytes();
+	private static final byte[] SERVER_KEY_BYTES = "Server Key".getBytes();
+
+	private static class KeyPair {
+		final byte[] clientKey;
+		final byte[] serverKey;
+
+		KeyPair(final byte[] clientKey, final byte[] serverKey) {
+			this.clientKey = clientKey;
+			this.serverKey = serverKey;
+		}
+	}
+
+	static {
+		CACHE = new LruCache<String, KeyPair>(10) {
+			protected KeyPair create(final String k) {
+				// Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
+				// Changing any of these values forces a cache miss. `CryptoHelper.bytesToHex()'
+				// is applied to prevent commas in the strings breaking things.
+				final String[] kparts = k.split(",", 4);
+				try {
+					final byte[] saltedPassword, serverKey, clientKey;
+					saltedPassword = hi(CryptoHelper.hexToString(kparts[1]).getBytes(),
+							Base64.decode(CryptoHelper.hexToString(kparts[2]), Base64.DEFAULT), Integer.valueOf(kparts[3]));
+					serverKey = hmac(saltedPassword, SERVER_KEY_BYTES);
+					clientKey = hmac(saltedPassword, CLIENT_KEY_BYTES);
+
+					return new KeyPair(clientKey, serverKey);
+				} catch (final InvalidKeyException | NumberFormatException e) {
+					return null;
+				}
+			}
+		};
+	}
+
+	private static final LruCache<String, KeyPair> CACHE;
+
+	protected State state = State.INITIAL;
+
+	ScramMechanism(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
+		super(tagWriter, account, rng);
+
+		// This nonce should be different for each authentication attempt.
+		clientNonce = new BigInteger(100, this.rng).toString(32);
+		clientFirstMessageBare = "";
+	}
+
+	@Override
+	public String getClientFirstMessage() {
+		if (clientFirstMessageBare.isEmpty() && state == State.INITIAL) {
+			clientFirstMessageBare = "n=" + CryptoHelper.saslEscape(CryptoHelper.saslPrep(account.getUsername())) +
+				",r=" + this.clientNonce;
+			state = State.AUTH_TEXT_SENT;
+		}
+		return Base64.encodeToString(
+				(GS2_HEADER + clientFirstMessageBare).getBytes(Charset.defaultCharset()),
+				Base64.NO_WRAP);
+	}
+
+	@Override
+	public String getResponse(final String challenge) throws AuthenticationException {
+		switch (state) {
+			case AUTH_TEXT_SENT:
+				if (challenge == null) {
+					throw new AuthenticationException("challenge can not be null");
+				}
+				byte[] serverFirstMessage = Base64.decode(challenge, Base64.DEFAULT);
+				final Tokenizer tokenizer = new Tokenizer(serverFirstMessage);
+				String nonce = "";
+				int iterationCount = -1;
+				String salt = "";
+				for (final String token : tokenizer) {
+					if (token.charAt(1) == '=') {
+						switch (token.charAt(0)) {
+							case 'i':
+								try {
+									iterationCount = Integer.parseInt(token.substring(2));
+								} catch (final NumberFormatException e) {
+									throw new AuthenticationException(e);
+								}
+								break;
+							case 's':
+								salt = token.substring(2);
+								break;
+							case 'r':
+								nonce = token.substring(2);
+								break;
+							case 'm':
+								/*
+								 * RFC 5802:
+								 * m: This attribute is reserved for future extensibility.  In this
+								 * version of SCRAM, its presence in a client or a server message
+								 * MUST cause authentication failure when the attribute is parsed by
+								 * the other end.
+								 */
+								throw new AuthenticationException("Server sent reserved token: `m'");
+						}
+					}
+				}
+
+				if (iterationCount < 0) {
+					throw new AuthenticationException("Server did not send iteration count");
+				}
+				if (nonce.isEmpty() || !nonce.startsWith(clientNonce)) {
+					throw new AuthenticationException("Server nonce does not contain client nonce: " + nonce);
+				}
+				if (salt.isEmpty()) {
+					throw new AuthenticationException("Server sent empty salt");
+				}
+
+				final String clientFinalMessageWithoutProof = "c=" + Base64.encodeToString(
+						GS2_HEADER.getBytes(), Base64.NO_WRAP) + ",r=" + nonce;
+				final byte[] authMessage = (clientFirstMessageBare + ',' + new String(serverFirstMessage) + ','
+						+ clientFinalMessageWithoutProof).getBytes();
+
+				// Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
+				final KeyPair keys = CACHE.get(
+						CryptoHelper.bytesToHex(account.getJid().toBareJid().toString().getBytes()) + ","
+						+ CryptoHelper.bytesToHex(account.getPassword().getBytes()) + ","
+						+ CryptoHelper.bytesToHex(salt.getBytes()) + ","
+						+ String.valueOf(iterationCount)
+						);
+				if (keys == null) {
+					throw new AuthenticationException("Invalid keys generated");
+				}
+				final byte[] clientSignature;
+				try {
+					serverSignature = hmac(keys.serverKey, authMessage);
+					final byte[] storedKey = digest(keys.clientKey);
+
+					clientSignature = hmac(storedKey, authMessage);
+
+				} catch (final InvalidKeyException e) {
+					throw new AuthenticationException(e);
+				}
+
+				final byte[] clientProof = new byte[keys.clientKey.length];
+
+				for (int i = 0; i < clientProof.length; i++) {
+					clientProof[i] = (byte) (keys.clientKey[i] ^ clientSignature[i]);
+				}
+
+
+				final String clientFinalMessage = clientFinalMessageWithoutProof + ",p=" +
+					Base64.encodeToString(clientProof, Base64.NO_WRAP);
+				state = State.RESPONSE_SENT;
+				return Base64.encodeToString(clientFinalMessage.getBytes(), Base64.NO_WRAP);
+			case RESPONSE_SENT:
+				try {
+					final String clientCalculatedServerFinalMessage = "v=" +
+						Base64.encodeToString(serverSignature, Base64.NO_WRAP);
+					if (!clientCalculatedServerFinalMessage.equals(new String(Base64.decode(challenge, Base64.DEFAULT)))) {
+						throw new Exception();
+					}
+					state = State.VALID_SERVER_RESPONSE;
+					return "";
+				} catch(Exception e) {
+					throw new AuthenticationException("Server final message does not match calculated final message");
+				}
+			default:
+				throw new InvalidStateException(state);
+		}
+	}
+
+	private static synchronized byte[] hmac(final byte[] key, final byte[] input)
+		throws InvalidKeyException {
+		HMAC.init(new KeyParameter(key));
+		HMAC.update(input, 0, input.length);
+		final byte[] out = new byte[HMAC.getMacSize()];
+		HMAC.doFinal(out, 0);
+		return out;
+	}
+
+	public static synchronized byte[] digest(byte[] bytes) {
+		DIGEST.reset();
+		DIGEST.update(bytes, 0, bytes.length);
+		final byte[] out = new byte[DIGEST.getDigestSize()];
+		DIGEST.doFinal(out, 0);
+		return out;
+	}
+
+	/*
+	 * Hi() is, essentially, PBKDF2 [RFC2898] with HMAC() as the
+	 * pseudorandom function (PRF) and with dkLen == output length of
+	 * HMAC() == output length of H().
+	 */
+	private static synchronized byte[] hi(final byte[] key, final byte[] salt, final int iterations)
+		throws InvalidKeyException {
+		byte[] u = hmac(key, CryptoHelper.concatenateByteArrays(salt, CryptoHelper.ONE));
+		byte[] out = u.clone();
+		for (int i = 1; i < iterations; i++) {
+			u = hmac(key, u);
+			for (int j = 0; j < u.length; j++) {
+				out[j] ^= u[j];
+			}
+		}
+		return out;
+	}
+}