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
31void 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
41static 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
54static 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
65int 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
112static 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
126int 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
238int 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
327#ifdef TEST
328#include <stdio.h>
329
330static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
331
332static const uint8_t rtp_aes128_80[] = {
333    // RTP header
334    0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
335    // encrypted payload
336    0x62, 0x69, 0x76, 0xca, 0xc5,
337    // HMAC
338    0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99,
339};
340
341static const uint8_t rtcp_aes128_80[] = {
342    // RTCP header
343    0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
344    // encrypted payload
345    0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda,
346    0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35,
347    // RTCP index
348    0x80, 0x00, 0x00, 0x03,
349    // HMAC
350    0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde,
351};
352
353static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
354
355static const uint8_t rtp_aes128_32[] = {
356    // RTP header
357    0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
358    // encrypted payload
359    0x62, 0x69, 0x76, 0xca, 0xc5,
360    // HMAC
361    0xa1, 0xac, 0x1b, 0xb4,
362};
363
364static const uint8_t rtcp_aes128_32[] = {
365    // RTCP header
366    0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
367    // encrypted payload
368    0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b,
369    0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34,
370    // RTCP index
371    0x80, 0x00, 0x00, 0x04,
372    // HMAC
373    0x5b, 0xd2, 0xa9, 0x9d,
374};
375
376static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
377
378static const uint8_t rtp_aes128_80_32[] = {
379    // RTP header
380    0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
381    // encrypted payload
382    0x62, 0x69, 0x76, 0xca, 0xc5,
383    // HMAC
384    0xa1, 0xac, 0x1b, 0xb4,
385};
386
387static const uint8_t rtcp_aes128_80_32[] = {
388    // RTCP header
389    0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
390    // encrypted payload
391    0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53,
392    0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9,
393    // RTCP index
394    0x80, 0x00, 0x00, 0x05,
395    // HMAC
396    0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10,
397};
398
399static void print_data(const uint8_t *buf, int len)
400{
401    int i;
402    for (i = 0; i < len; i++)
403        printf("%02x", buf[i]);
404    printf("\n");
405}
406
407static int test_decrypt(struct SRTPContext *srtp, const uint8_t *in, int len,
408                        uint8_t *out)
409{
410    memcpy(out, in, len);
411    if (!ff_srtp_decrypt(srtp, out, &len)) {
412        print_data(out, len);
413        return len;
414    } else
415        return -1;
416}
417
418static void test_encrypt(const uint8_t *data, int in_len, const char *suite,
419                         const char *key)
420{
421    struct SRTPContext enc = { 0 }, dec = { 0 };
422    int len;
423    char buf[RTP_MAX_PACKET_LENGTH];
424    ff_srtp_set_crypto(&enc, suite, key);
425    ff_srtp_set_crypto(&dec, suite, key);
426    len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf));
427    if (!ff_srtp_decrypt(&dec, buf, &len)) {
428        if (len == in_len && !memcmp(buf, data, len))
429            printf("Decrypted content matches input\n");
430        else
431            printf("Decrypted content doesn't match input\n");
432    } else {
433        printf("Decryption failed\n");
434    }
435    ff_srtp_free(&enc);
436    ff_srtp_free(&dec);
437}
438
439int main(void)
440{
441    static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80";
442    static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32";
443    static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32";
444    static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD";
445    uint8_t buf[RTP_MAX_PACKET_LENGTH];
446    struct SRTPContext srtp = { 0 };
447    int len;
448    ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key);
449    len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf);
450    test_encrypt(buf, len, aes128_80_suite, test_key);
451    test_encrypt(buf, len, aes128_32_suite, test_key);
452    test_encrypt(buf, len, aes128_80_32_suite, test_key);
453    test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf);
454    test_encrypt(buf, len, aes128_80_suite, test_key);
455    test_encrypt(buf, len, aes128_32_suite, test_key);
456    test_encrypt(buf, len, aes128_80_32_suite, test_key);
457    ff_srtp_free(&srtp);
458
459    memset(&srtp, 0, sizeof(srtp)); // Clear the context
460    ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key);
461    test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf);
462    test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf);
463    ff_srtp_free(&srtp);
464
465    memset(&srtp, 0, sizeof(srtp)); // Clear the context
466    ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key);
467    test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf);
468    test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf);
469    ff_srtp_free(&srtp);
470    return 0;
471}
472#endif /* TEST */
473