1package eu.siacs.conversations.crypto.sasl;
2
3import android.util.Base64;
4import android.util.LruCache;
5
6import org.bouncycastle.crypto.Digest;
7import org.bouncycastle.crypto.digests.SHA1Digest;
8import org.bouncycastle.crypto.macs.HMac;
9import org.bouncycastle.crypto.params.KeyParameter;
10
11import java.math.BigInteger;
12import java.nio.charset.Charset;
13import java.security.InvalidKeyException;
14import java.security.SecureRandom;
15
16import eu.siacs.conversations.entities.Account;
17import eu.siacs.conversations.utils.CryptoHelper;
18import eu.siacs.conversations.xml.TagWriter;
19
20public class ScramSha1 extends SaslMechanism {
21 // TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to indicate support and/or usage.
22 final private static String GS2_HEADER = "n,,";
23 private String clientFirstMessageBare;
24 private byte[] serverFirstMessage;
25 final private String clientNonce;
26 private byte[] serverSignature = null;
27 private static HMac HMAC;
28 private static Digest DIGEST;
29 private static final byte[] CLIENT_KEY_BYTES = "Client Key".getBytes();
30 private static final byte[] SERVER_KEY_BYTES = "Server Key".getBytes();
31
32 public static class KeyPair {
33 final public byte[] clientKey;
34 final public byte[] serverKey;
35
36 public KeyPair(final byte[] clientKey, final byte[] serverKey) {
37 this.clientKey = clientKey;
38 this.serverKey = serverKey;
39 }
40 }
41
42 private static final LruCache<String, KeyPair> CACHE;
43
44 static {
45 DIGEST = new SHA1Digest();
46 HMAC = new HMac(new SHA1Digest());
47 CACHE = new LruCache<String, KeyPair>(10) {
48 protected KeyPair create(final String k) {
49 // Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
50 // Changing any of these values forces a cache miss. `CryptoHelper.bytesToHex()'
51 // is applied to prevent commas in the strings breaking things.
52 final String[] kparts = k.split(",", 4);
53 try {
54 final byte[] saltedPassword, serverKey, clientKey;
55 saltedPassword = hi(CryptoHelper.hexToString(kparts[1]).getBytes(),
56 Base64.decode(CryptoHelper.hexToString(kparts[2]), Base64.DEFAULT), Integer.valueOf(kparts[3]));
57 serverKey = hmac(saltedPassword, SERVER_KEY_BYTES);
58 clientKey = hmac(saltedPassword, CLIENT_KEY_BYTES);
59
60 return new KeyPair(clientKey, serverKey);
61 } catch (final InvalidKeyException | NumberFormatException e) {
62 return null;
63 }
64 }
65 };
66 }
67
68 private State state = State.INITIAL;
69
70 public ScramSha1(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
71 super(tagWriter, account, rng);
72
73 // This nonce should be different for each authentication attempt.
74 clientNonce = new BigInteger(100, this.rng).toString(32);
75 clientFirstMessageBare = "";
76 }
77
78 @Override
79 public int getPriority() {
80 return 20;
81 }
82
83 @Override
84 public String getMechanism() {
85 return "SCRAM-SHA-1";
86 }
87
88 @Override
89 public String getClientFirstMessage() {
90 if (clientFirstMessageBare.isEmpty() && state == State.INITIAL) {
91 clientFirstMessageBare = "n=" + CryptoHelper.saslEscape(CryptoHelper.saslPrep(account.getUsername())) +
92 ",r=" + this.clientNonce;
93 state = State.AUTH_TEXT_SENT;
94 }
95 return Base64.encodeToString(
96 (GS2_HEADER + clientFirstMessageBare).getBytes(Charset.defaultCharset()),
97 Base64.NO_WRAP);
98 }
99
100 @Override
101 public String getResponse(final String challenge) throws AuthenticationException {
102 switch (state) {
103 case AUTH_TEXT_SENT:
104 if (challenge == null) {
105 throw new AuthenticationException("challenge can not be null");
106 }
107 serverFirstMessage = Base64.decode(challenge, Base64.DEFAULT);
108 final Tokenizer tokenizer = new Tokenizer(serverFirstMessage);
109 String nonce = "";
110 int iterationCount = -1;
111 String salt = "";
112 for (final String token : tokenizer) {
113 if (token.charAt(1) == '=') {
114 switch (token.charAt(0)) {
115 case 'i':
116 try {
117 iterationCount = Integer.parseInt(token.substring(2));
118 } catch (final NumberFormatException e) {
119 throw new AuthenticationException(e);
120 }
121 break;
122 case 's':
123 salt = token.substring(2);
124 break;
125 case 'r':
126 nonce = token.substring(2);
127 break;
128 case 'm':
129 /*
130 * RFC 5802:
131 * m: This attribute is reserved for future extensibility. In this
132 * version of SCRAM, its presence in a client or a server message
133 * MUST cause authentication failure when the attribute is parsed by
134 * the other end.
135 */
136 throw new AuthenticationException("Server sent reserved token: `m'");
137 }
138 }
139 }
140
141 if (iterationCount < 0) {
142 throw new AuthenticationException("Server did not send iteration count");
143 }
144 if (nonce.isEmpty() || !nonce.startsWith(clientNonce)) {
145 throw new AuthenticationException("Server nonce does not contain client nonce: " + nonce);
146 }
147 if (salt.isEmpty()) {
148 throw new AuthenticationException("Server sent empty salt");
149 }
150
151 final String clientFinalMessageWithoutProof = "c=" + Base64.encodeToString(
152 GS2_HEADER.getBytes(), Base64.NO_WRAP) + ",r=" + nonce;
153 final byte[] authMessage = (clientFirstMessageBare + ',' + new String(serverFirstMessage) + ','
154 + clientFinalMessageWithoutProof).getBytes();
155
156 // Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
157 final KeyPair keys = CACHE.get(
158 CryptoHelper.bytesToHex(account.getJid().toBareJid().toString().getBytes()) + ","
159 + CryptoHelper.bytesToHex(account.getPassword().getBytes()) + ","
160 + CryptoHelper.bytesToHex(salt.getBytes()) + ","
161 + String.valueOf(iterationCount)
162 );
163 if (keys == null) {
164 throw new AuthenticationException("Invalid keys generated");
165 }
166 final byte[] clientSignature;
167 try {
168 serverSignature = hmac(keys.serverKey, authMessage);
169 final byte[] storedKey = digest(keys.clientKey);
170
171 clientSignature = hmac(storedKey, authMessage);
172
173 } catch (final InvalidKeyException e) {
174 throw new AuthenticationException(e);
175 }
176
177 final byte[] clientProof = new byte[keys.clientKey.length];
178
179 for (int i = 0; i < clientProof.length; i++) {
180 clientProof[i] = (byte) (keys.clientKey[i] ^ clientSignature[i]);
181 }
182
183
184 final String clientFinalMessage = clientFinalMessageWithoutProof + ",p=" +
185 Base64.encodeToString(clientProof, Base64.NO_WRAP);
186 state = State.RESPONSE_SENT;
187 return Base64.encodeToString(clientFinalMessage.getBytes(), Base64.NO_WRAP);
188 case RESPONSE_SENT:
189 final String clientCalculatedServerFinalMessage = "v=" +
190 Base64.encodeToString(serverSignature, Base64.NO_WRAP);
191 if (challenge == null || !clientCalculatedServerFinalMessage.equals(new String(Base64.decode(challenge, Base64.DEFAULT)))) {
192 throw new AuthenticationException("Server final message does not match calculated final message");
193 }
194 state = State.VALID_SERVER_RESPONSE;
195 return "";
196 default:
197 throw new InvalidStateException(state);
198 }
199 }
200
201 public static synchronized byte[] hmac(final byte[] key, final byte[] input)
202 throws InvalidKeyException {
203 HMAC.init(new KeyParameter(key));
204 HMAC.update(input, 0, input.length);
205 final byte[] out = new byte[HMAC.getMacSize()];
206 HMAC.doFinal(out, 0);
207 return out;
208 }
209
210 public static synchronized byte[] digest(byte[] bytes) {
211 DIGEST.reset();
212 DIGEST.update(bytes, 0, bytes.length);
213 final byte[] out = new byte[DIGEST.getDigestSize()];
214 DIGEST.doFinal(out, 0);
215 return out;
216 }
217
218 /*
219 * Hi() is, essentially, PBKDF2 [RFC2898] with HMAC() as the
220 * pseudorandom function (PRF) and with dkLen == output length of
221 * HMAC() == output length of H().
222 */
223 private static synchronized byte[] hi(final byte[] key, final byte[] salt, final int iterations)
224 throws InvalidKeyException {
225 byte[] u = hmac(key, CryptoHelper.concatenateByteArrays(salt, CryptoHelper.ONE));
226 byte[] out = u.clone();
227 for (int i = 1; i < iterations; i++) {
228 u = hmac(key, u);
229 for (int j = 0; j < u.length; j++) {
230 out[j] ^= u[j];
231 }
232 }
233 return out;
234 }
235}