blob: f8b686c5aaa71caf3b83388c8f7d41ca38a6e9af
1 | /* |
2 | * SRTP encryption/decryption |
3 | * Copyright (c) 2012 Martin Storsjo |
4 | * |
5 | * This file is part of FFmpeg. |
6 | * |
7 | * FFmpeg is free software; you can redistribute it and/or |
8 | * modify it under the terms of the GNU Lesser General Public |
9 | * License as published by the Free Software Foundation; either |
10 | * version 2.1 of the License, or (at your option) any later version. |
11 | * |
12 | * FFmpeg is distributed in the hope that it will be useful, |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
15 | * Lesser General Public License for more details. |
16 | * |
17 | * You should have received a copy of the GNU Lesser General Public |
18 | * License along with FFmpeg; if not, write to the Free Software |
19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
20 | */ |
21 | |
22 | #include "libavutil/base64.h" |
23 | #include "libavutil/aes.h" |
24 | #include "libavutil/hmac.h" |
25 | #include "libavutil/intreadwrite.h" |
26 | #include "libavutil/log.h" |
27 | #include "rtp.h" |
28 | #include "rtpdec.h" |
29 | #include "srtp.h" |
30 | |
31 | void ff_srtp_free(struct SRTPContext *s) |
32 | { |
33 | if (!s) |
34 | return; |
35 | av_freep(&s->aes); |
36 | if (s->hmac) |
37 | av_hmac_free(s->hmac); |
38 | s->hmac = NULL; |
39 | } |
40 | |
41 | static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf, |
42 | int outlen) |
43 | { |
44 | int i, j, outpos; |
45 | for (i = 0, outpos = 0; outpos < outlen; i++) { |
46 | uint8_t keystream[16]; |
47 | AV_WB16(&iv[14], i); |
48 | av_aes_crypt(aes, keystream, iv, 1, NULL, 0); |
49 | for (j = 0; j < 16 && outpos < outlen; j++, outpos++) |
50 | outbuf[outpos] ^= keystream[j]; |
51 | } |
52 | } |
53 | |
54 | static void derive_key(struct AVAES *aes, const uint8_t *salt, int label, |
55 | uint8_t *out, int outlen) |
56 | { |
57 | uint8_t input[16] = { 0 }; |
58 | memcpy(input, salt, 14); |
59 | // Key derivation rate assumed to be zero |
60 | input[14 - 7] ^= label; |
61 | memset(out, 0, outlen); |
62 | encrypt_counter(aes, input, out, outlen); |
63 | } |
64 | |
65 | int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite, |
66 | const char *params) |
67 | { |
68 | uint8_t buf[30]; |
69 | |
70 | ff_srtp_free(s); |
71 | |
72 | // RFC 4568 |
73 | if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") || |
74 | !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) { |
75 | s->rtp_hmac_size = s->rtcp_hmac_size = 10; |
76 | } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) { |
77 | s->rtp_hmac_size = s->rtcp_hmac_size = 4; |
78 | } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) { |
79 | // RFC 5764 section 4.1.2 |
80 | s->rtp_hmac_size = 4; |
81 | s->rtcp_hmac_size = 10; |
82 | } else { |
83 | av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n", |
84 | suite); |
85 | return AVERROR(EINVAL); |
86 | } |
87 | if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) { |
88 | av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n"); |
89 | return AVERROR(EINVAL); |
90 | } |
91 | // MKI and lifetime not handled yet |
92 | s->aes = av_aes_alloc(); |
93 | s->hmac = av_hmac_alloc(AV_HMAC_SHA1); |
94 | if (!s->aes || !s->hmac) |
95 | return AVERROR(ENOMEM); |
96 | memcpy(s->master_key, buf, 16); |
97 | memcpy(s->master_salt, buf + 16, 14); |
98 | |
99 | // RFC 3711 |
100 | av_aes_init(s->aes, s->master_key, 128, 0); |
101 | |
102 | derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key)); |
103 | derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt)); |
104 | derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth)); |
105 | |
106 | derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key)); |
107 | derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt)); |
108 | derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth)); |
109 | return 0; |
110 | } |
111 | |
112 | static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index, |
113 | uint32_t ssrc) |
114 | { |
115 | uint8_t indexbuf[8]; |
116 | int i; |
117 | memset(iv, 0, 16); |
118 | AV_WB32(&iv[4], ssrc); |
119 | AV_WB64(indexbuf, index); |
120 | for (i = 0; i < 8; i++) // index << 16 |
121 | iv[6 + i] ^= indexbuf[i]; |
122 | for (i = 0; i < 14; i++) |
123 | iv[i] ^= salt[i]; |
124 | } |
125 | |
126 | int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr) |
127 | { |
128 | uint8_t iv[16] = { 0 }, hmac[20]; |
129 | int len = *lenptr; |
130 | int av_uninit(seq_largest); |
131 | uint32_t ssrc, av_uninit(roc); |
132 | uint64_t index; |
133 | int rtcp, hmac_size; |
134 | |
135 | // TODO: Missing replay protection |
136 | |
137 | if (len < 2) |
138 | return AVERROR_INVALIDDATA; |
139 | |
140 | rtcp = RTP_PT_IS_RTCP(buf[1]); |
141 | hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size; |
142 | |
143 | if (len < hmac_size) |
144 | return AVERROR_INVALIDDATA; |
145 | |
146 | // Authentication HMAC |
147 | av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth)); |
148 | // If MKI is used, this should exclude the MKI as well |
149 | av_hmac_update(s->hmac, buf, len - hmac_size); |
150 | |
151 | if (!rtcp) { |
152 | int seq = AV_RB16(buf + 2); |
153 | uint32_t v; |
154 | uint8_t rocbuf[4]; |
155 | |
156 | // RFC 3711 section 3.3.1, appendix A |
157 | seq_largest = s->seq_initialized ? s->seq_largest : seq; |
158 | v = roc = s->roc; |
159 | if (seq_largest < 32768) { |
160 | if (seq - seq_largest > 32768) |
161 | v = roc - 1; |
162 | } else { |
163 | if (seq_largest - 32768 > seq) |
164 | v = roc + 1; |
165 | } |
166 | if (v == roc) { |
167 | seq_largest = FFMAX(seq_largest, seq); |
168 | } else if (v == roc + 1) { |
169 | seq_largest = seq; |
170 | roc = v; |
171 | } |
172 | index = seq + (((uint64_t)v) << 16); |
173 | |
174 | AV_WB32(rocbuf, roc); |
175 | av_hmac_update(s->hmac, rocbuf, 4); |
176 | } |
177 | |
178 | av_hmac_final(s->hmac, hmac, sizeof(hmac)); |
179 | if (memcmp(hmac, buf + len - hmac_size, hmac_size)) { |
180 | av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n"); |
181 | return AVERROR_INVALIDDATA; |
182 | } |
183 | |
184 | len -= hmac_size; |
185 | *lenptr = len; |
186 | |
187 | if (len < 12) |
188 | return AVERROR_INVALIDDATA; |
189 | |
190 | if (rtcp) { |
191 | uint32_t srtcp_index = AV_RB32(buf + len - 4); |
192 | len -= 4; |
193 | *lenptr = len; |
194 | |
195 | ssrc = AV_RB32(buf + 4); |
196 | index = srtcp_index & 0x7fffffff; |
197 | |
198 | buf += 8; |
199 | len -= 8; |
200 | if (!(srtcp_index & 0x80000000)) |
201 | return 0; |
202 | } else { |
203 | int ext, csrc; |
204 | s->seq_initialized = 1; |
205 | s->seq_largest = seq_largest; |
206 | s->roc = roc; |
207 | |
208 | csrc = buf[0] & 0x0f; |
209 | ext = buf[0] & 0x10; |
210 | ssrc = AV_RB32(buf + 8); |
211 | |
212 | buf += 12; |
213 | len -= 12; |
214 | |
215 | buf += 4 * csrc; |
216 | len -= 4 * csrc; |
217 | if (len < 0) |
218 | return AVERROR_INVALIDDATA; |
219 | |
220 | if (ext) { |
221 | if (len < 4) |
222 | return AVERROR_INVALIDDATA; |
223 | ext = (AV_RB16(buf + 2) + 1) * 4; |
224 | if (len < ext) |
225 | return AVERROR_INVALIDDATA; |
226 | len -= ext; |
227 | buf += ext; |
228 | } |
229 | } |
230 | |
231 | create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc); |
232 | av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0); |
233 | encrypt_counter(s->aes, iv, buf, len); |
234 | |
235 | return 0; |
236 | } |
237 | |
238 | int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len, |
239 | uint8_t *out, int outlen) |
240 | { |
241 | uint8_t iv[16] = { 0 }, hmac[20]; |
242 | uint64_t index; |
243 | uint32_t ssrc; |
244 | int rtcp, hmac_size, padding; |
245 | uint8_t *buf; |
246 | |
247 | if (len < 8) |
248 | return AVERROR_INVALIDDATA; |
249 | |
250 | rtcp = RTP_PT_IS_RTCP(in[1]); |
251 | hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size; |
252 | padding = hmac_size; |
253 | if (rtcp) |
254 | padding += 4; // For the RTCP index |
255 | |
256 | if (len + padding > outlen) |
257 | return 0; |
258 | |
259 | memcpy(out, in, len); |
260 | buf = out; |
261 | |
262 | if (rtcp) { |
263 | ssrc = AV_RB32(buf + 4); |
264 | index = s->rtcp_index++; |
265 | |
266 | buf += 8; |
267 | len -= 8; |
268 | } else { |
269 | int ext, csrc; |
270 | int seq = AV_RB16(buf + 2); |
271 | |
272 | if (len < 12) |
273 | return AVERROR_INVALIDDATA; |
274 | |
275 | ssrc = AV_RB32(buf + 8); |
276 | |
277 | if (seq < s->seq_largest) |
278 | s->roc++; |
279 | s->seq_largest = seq; |
280 | index = seq + (((uint64_t)s->roc) << 16); |
281 | |
282 | csrc = buf[0] & 0x0f; |
283 | ext = buf[0] & 0x10; |
284 | |
285 | buf += 12; |
286 | len -= 12; |
287 | |
288 | buf += 4 * csrc; |
289 | len -= 4 * csrc; |
290 | if (len < 0) |
291 | return AVERROR_INVALIDDATA; |
292 | |
293 | if (ext) { |
294 | if (len < 4) |
295 | return AVERROR_INVALIDDATA; |
296 | ext = (AV_RB16(buf + 2) + 1) * 4; |
297 | if (len < ext) |
298 | return AVERROR_INVALIDDATA; |
299 | len -= ext; |
300 | buf += ext; |
301 | } |
302 | } |
303 | |
304 | create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc); |
305 | av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0); |
306 | encrypt_counter(s->aes, iv, buf, len); |
307 | |
308 | if (rtcp) { |
309 | AV_WB32(buf + len, 0x80000000 | index); |
310 | len += 4; |
311 | } |
312 | |
313 | av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth)); |
314 | av_hmac_update(s->hmac, out, buf + len - out); |
315 | if (!rtcp) { |
316 | uint8_t rocbuf[4]; |
317 | AV_WB32(rocbuf, s->roc); |
318 | av_hmac_update(s->hmac, rocbuf, 4); |
319 | } |
320 | av_hmac_final(s->hmac, hmac, sizeof(hmac)); |
321 | |
322 | memcpy(buf + len, hmac, hmac_size); |
323 | len += hmac_size; |
324 | return buf + len - out; |
325 | } |
326 |