1package eu.siacs.conversations.crypto.sasl;
2
3import android.annotation.TargetApi;
4import android.os.Build;
5import android.util.Base64;
6import android.util.LruCache;
7
8import org.bouncycastle.crypto.Digest;
9import org.bouncycastle.crypto.macs.HMac;
10import org.bouncycastle.crypto.params.KeyParameter;
11
12import java.math.BigInteger;
13import java.nio.charset.Charset;
14import java.security.InvalidKeyException;
15import java.security.SecureRandom;
16
17import eu.siacs.conversations.entities.Account;
18import eu.siacs.conversations.utils.CryptoHelper;
19import eu.siacs.conversations.xml.TagWriter;
20
21@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
22abstract class ScramMechanism extends SaslMechanism {
23 // TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to indicate support and/or usage.
24 private final static String GS2_HEADER = "n,,";
25 private String clientFirstMessageBare;
26 private final String clientNonce;
27 private byte[] serverSignature = null;
28 static HMac HMAC;
29 static Digest DIGEST;
30 private static final byte[] CLIENT_KEY_BYTES = "Client Key".getBytes();
31 private static final byte[] SERVER_KEY_BYTES = "Server Key".getBytes();
32
33 private static class KeyPair {
34 final byte[] clientKey;
35 final byte[] serverKey;
36
37 KeyPair(final byte[] clientKey, final byte[] serverKey) {
38 this.clientKey = clientKey;
39 this.serverKey = serverKey;
40 }
41 }
42
43 static {
44 CACHE = new LruCache<String, KeyPair>(10) {
45 protected KeyPair create(final String k) {
46 // Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
47 // Changing any of these values forces a cache miss. `CryptoHelper.bytesToHex()'
48 // is applied to prevent commas in the strings breaking things.
49 final String[] kparts = k.split(",", 4);
50 try {
51 final byte[] saltedPassword, serverKey, clientKey;
52 saltedPassword = hi(CryptoHelper.hexToString(kparts[1]).getBytes(),
53 Base64.decode(CryptoHelper.hexToString(kparts[2]), Base64.DEFAULT), Integer.valueOf(kparts[3]));
54 serverKey = hmac(saltedPassword, SERVER_KEY_BYTES);
55 clientKey = hmac(saltedPassword, CLIENT_KEY_BYTES);
56
57 return new KeyPair(clientKey, serverKey);
58 } catch (final InvalidKeyException | NumberFormatException e) {
59 return null;
60 }
61 }
62 };
63 }
64
65 private static final LruCache<String, KeyPair> CACHE;
66
67 protected State state = State.INITIAL;
68
69 ScramMechanism(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
70 super(tagWriter, account, rng);
71
72 // This nonce should be different for each authentication attempt.
73 clientNonce = new BigInteger(100, this.rng).toString(32);
74 clientFirstMessageBare = "";
75 }
76
77 @Override
78 public String getClientFirstMessage() {
79 if (clientFirstMessageBare.isEmpty() && state == State.INITIAL) {
80 clientFirstMessageBare = "n=" + CryptoHelper.saslEscape(CryptoHelper.saslPrep(account.getUsername())) +
81 ",r=" + this.clientNonce;
82 state = State.AUTH_TEXT_SENT;
83 }
84 return Base64.encodeToString(
85 (GS2_HEADER + clientFirstMessageBare).getBytes(Charset.defaultCharset()),
86 Base64.NO_WRAP);
87 }
88
89 @Override
90 public String getResponse(final String challenge) throws AuthenticationException {
91 switch (state) {
92 case AUTH_TEXT_SENT:
93 if (challenge == null) {
94 throw new AuthenticationException("challenge can not be null");
95 }
96 byte[] serverFirstMessage = Base64.decode(challenge, Base64.DEFAULT);
97 final Tokenizer tokenizer = new Tokenizer(serverFirstMessage);
98 String nonce = "";
99 int iterationCount = -1;
100 String salt = "";
101 for (final String token : tokenizer) {
102 if (token.charAt(1) == '=') {
103 switch (token.charAt(0)) {
104 case 'i':
105 try {
106 iterationCount = Integer.parseInt(token.substring(2));
107 } catch (final NumberFormatException e) {
108 throw new AuthenticationException(e);
109 }
110 break;
111 case 's':
112 salt = token.substring(2);
113 break;
114 case 'r':
115 nonce = token.substring(2);
116 break;
117 case 'm':
118 /*
119 * RFC 5802:
120 * m: This attribute is reserved for future extensibility. In this
121 * version of SCRAM, its presence in a client or a server message
122 * MUST cause authentication failure when the attribute is parsed by
123 * the other end.
124 */
125 throw new AuthenticationException("Server sent reserved token: `m'");
126 }
127 }
128 }
129
130 if (iterationCount < 0) {
131 throw new AuthenticationException("Server did not send iteration count");
132 }
133 if (nonce.isEmpty() || !nonce.startsWith(clientNonce)) {
134 throw new AuthenticationException("Server nonce does not contain client nonce: " + nonce);
135 }
136 if (salt.isEmpty()) {
137 throw new AuthenticationException("Server sent empty salt");
138 }
139
140 final String clientFinalMessageWithoutProof = "c=" + Base64.encodeToString(
141 GS2_HEADER.getBytes(), Base64.NO_WRAP) + ",r=" + nonce;
142 final byte[] authMessage = (clientFirstMessageBare + ',' + new String(serverFirstMessage) + ','
143 + clientFinalMessageWithoutProof).getBytes();
144
145 // Map keys are "bytesToHex(JID),bytesToHex(password),bytesToHex(salt),iterations".
146 final KeyPair keys = CACHE.get(
147 CryptoHelper.bytesToHex(account.getJid().toBareJid().toString().getBytes()) + ","
148 + CryptoHelper.bytesToHex(account.getPassword().getBytes()) + ","
149 + CryptoHelper.bytesToHex(salt.getBytes()) + ","
150 + String.valueOf(iterationCount)
151 );
152 if (keys == null) {
153 throw new AuthenticationException("Invalid keys generated");
154 }
155 final byte[] clientSignature;
156 try {
157 serverSignature = hmac(keys.serverKey, authMessage);
158 final byte[] storedKey = digest(keys.clientKey);
159
160 clientSignature = hmac(storedKey, authMessage);
161
162 } catch (final InvalidKeyException e) {
163 throw new AuthenticationException(e);
164 }
165
166 final byte[] clientProof = new byte[keys.clientKey.length];
167
168 for (int i = 0; i < clientProof.length; i++) {
169 clientProof[i] = (byte) (keys.clientKey[i] ^ clientSignature[i]);
170 }
171
172
173 final String clientFinalMessage = clientFinalMessageWithoutProof + ",p=" +
174 Base64.encodeToString(clientProof, Base64.NO_WRAP);
175 state = State.RESPONSE_SENT;
176 return Base64.encodeToString(clientFinalMessage.getBytes(), Base64.NO_WRAP);
177 case RESPONSE_SENT:
178 try {
179 final String clientCalculatedServerFinalMessage = "v=" +
180 Base64.encodeToString(serverSignature, Base64.NO_WRAP);
181 if (!clientCalculatedServerFinalMessage.equals(new String(Base64.decode(challenge, Base64.DEFAULT)))) {
182 throw new Exception();
183 }
184 state = State.VALID_SERVER_RESPONSE;
185 return "";
186 } catch(Exception e) {
187 throw new AuthenticationException("Server final message does not match calculated final message");
188 }
189 default:
190 throw new InvalidStateException(state);
191 }
192 }
193
194 private static synchronized byte[] hmac(final byte[] key, final byte[] input)
195 throws InvalidKeyException {
196 HMAC.init(new KeyParameter(key));
197 HMAC.update(input, 0, input.length);
198 final byte[] out = new byte[HMAC.getMacSize()];
199 HMAC.doFinal(out, 0);
200 return out;
201 }
202
203 public static synchronized byte[] digest(byte[] bytes) {
204 DIGEST.reset();
205 DIGEST.update(bytes, 0, bytes.length);
206 final byte[] out = new byte[DIGEST.getDigestSize()];
207 DIGEST.doFinal(out, 0);
208 return out;
209 }
210
211 /*
212 * Hi() is, essentially, PBKDF2 [RFC2898] with HMAC() as the
213 * pseudorandom function (PRF) and with dkLen == output length of
214 * HMAC() == output length of H().
215 */
216 private static synchronized byte[] hi(final byte[] key, final byte[] salt, final int iterations)
217 throws InvalidKeyException {
218 byte[] u = hmac(key, CryptoHelper.concatenateByteArrays(salt, CryptoHelper.ONE));
219 byte[] out = u.clone();
220 for (int i = 1; i < iterations; i++) {
221 u = hmac(key, u);
222 for (int j = 0; j < u.length; j++) {
223 out[j] ^= u[j];
224 }
225 }
226 return out;
227 }
228}