Line data    Source code

       1             : /*
       2             :  * SRTP encryption/decryption
       3             :  * Copyright (c) 2012 Martin Storsjo
       4             :  *
       5             :  * This file is part of Libav.
       6             :  *
       7             :  * Libav 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             :  * Libav 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 Libav; if not, write to the Free Software
      19             :  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
      20             :  */
      21             : 
      22             : #include <stdlib.h>
      23             : #include <assert.h>
      24             : #include <libavutil/common.h>
      25             : #include <libavutil/base64.h>
      26             : #include <libavutil/aes.h>
      27             : #include <libavutil/hmac.h>
      28             : #include <libavutil/intreadwrite.h>
      29             : #include <libavutil/log.h>
      30             : #include "srtp.h"
      31             : 
      32             : #include "connectivity/security/memory.h"
      33             : 
      34        1695 : void ff_srtp_free(struct SRTPContext *s)
      35             : {
      36        1695 :     uint8_t zero_buffer[32] = {0}; // WARNING: must be long enough to handle any key length
      37             :     assert(sizeof(zero_buffer) >= sizeof(s->master_key));
      38             :     assert(sizeof(zero_buffer) >= sizeof(s->rtp_key));
      39             :     assert(sizeof(zero_buffer) >= sizeof(s->rtp_auth));
      40             : 
      41        1695 :     if (!s)
      42           0 :         return;
      43             :     // aes and hmac have an opaque pointer type.
      44             :     // No API to safely erase them, so just re-init with "dummy keys" to sanitize them
      45        1695 :     if (s->aes) {
      46         680 :         av_aes_init(s->aes, zero_buffer, 128, 0);
      47         680 :         av_freep(&s->aes);
      48             :     }
      49        1695 :     if (s->hmac) {
      50         680 :         av_hmac_init(s->hmac, zero_buffer, sizeof(s->rtp_auth));
      51         680 :         av_hmac_free(s->hmac);
      52             :     }
      53        1695 :     ring_secure_memzero(s, sizeof(*s));
      54             : }
      55             : 
      56       15801 : static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf,
      57             :                             int outlen)
      58             : {
      59             :     int i, j, outpos;
      60      171161 :     for (i = 0, outpos = 0; outpos < outlen; i++) {
      61             :         uint8_t keystream[16];
      62      155360 :         AV_WB16(&iv[14], i);
      63      155360 :         av_aes_crypt(aes, keystream, iv, 1, NULL, 0);
      64     2548711 :         for (j = 0; j < 16 && outpos < outlen; j++, outpos++)
      65     2393351 :             outbuf[outpos] ^= keystream[j];
      66             :     }
      67       15801 : }
      68             : 
      69        4080 : static void derive_key(struct AVAES *aes, const uint8_t *salt, int label,
      70             :                        uint8_t *out, int outlen)
      71             : {
      72        4080 :     uint8_t input[16] = { 0 };
      73        4080 :     memcpy(input, salt, 14);
      74             :     // Key derivation rate assumed to be zero
      75        4080 :     input[14 - 7] ^= label;
      76        4080 :     memset(out, 0, outlen);
      77        4080 :     encrypt_counter(aes, input, out, outlen);
      78        4080 : }
      79             : 
      80         680 : int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite,
      81             :                        const char *params)
      82             : {
      83             :     uint8_t buf[30];
      84             : 
      85         680 :     ff_srtp_free(s);
      86             : 
      87             :     // RFC 4568
      88         680 :     if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") ||
      89           0 :         !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) {
      90         680 :         s->rtp_hmac_size = s->rtcp_hmac_size = 10;
      91           0 :     } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
      92           0 :         s->rtp_hmac_size = s->rtcp_hmac_size = 4;
      93           0 :     } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) {
      94             :         // RFC 5764 section 4.1.2
      95           0 :         s->rtp_hmac_size  = 4;
      96           0 :         s->rtcp_hmac_size = 10;
      97             :     } else {
      98           0 :         av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n",
      99             :                                      suite);
     100           0 :         return AVERROR(EINVAL);
     101             :     }
     102         680 :     if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) {
     103           0 :         av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n");
     104           0 :         ring_secure_memzero(buf, sizeof(buf));
     105           0 :         return AVERROR(EINVAL);
     106             :     }
     107             :     // MKI and lifetime not handled yet
     108         680 :     s->aes  = av_aes_alloc();
     109         680 :     s->hmac = av_hmac_alloc(AV_HMAC_SHA1);
     110         680 :     if (!s->aes || !s->hmac)
     111           0 :         return AVERROR(ENOMEM);
     112         680 :     memcpy(s->master_key, buf, 16);
     113         680 :     memcpy(s->master_salt, buf + 16, 14);
     114         680 :     ring_secure_memzero(buf, sizeof(buf));
     115             : 
     116             :     // RFC 3711
     117         680 :     av_aes_init(s->aes, s->master_key, 128, 0);
     118             : 
     119         680 :     derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key));
     120         680 :     derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt));
     121         680 :     derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth));
     122             : 
     123         680 :     derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key));
     124         680 :     derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt));
     125         680 :     derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth));
     126         680 :     return 0;
     127             : }
     128             : 
     129       11721 : static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index,
     130             :                       uint32_t ssrc)
     131             : {
     132             :     uint8_t indexbuf[8];
     133             :     int i;
     134       11721 :     memset(iv, 0, 16);
     135       11721 :     AV_WB32(&iv[4], ssrc);
     136       11721 :     AV_WB64(indexbuf, index);
     137      105489 :     for (i = 0; i < 8; i++) // index << 16
     138       93768 :         iv[6 + i] ^= indexbuf[i];
     139      175815 :     for (i = 0; i < 14; i++)
     140      164094 :         iv[i] ^= salt[i];
     141       11721 :     ring_secure_memzero(indexbuf, sizeof(indexbuf));
     142       11721 : }
     143             : 
     144        5856 : int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr)
     145             : {
     146        5856 :     uint8_t iv[16] = { 0 }, hmac[20];
     147        5856 :     int len = *lenptr;
     148             : #ifdef _MSC_VER
     149             : #pragma message (__FILE__ "(" STR2(__LINE__) ") : -NOTE- " seq_largest and roc may be unitialized)
     150             : #else
     151             : #warning seq_largest and roc may be unitialized
     152             : #endif
     153        5856 :     int av_uninit(seq_largest);
     154        5856 :     uint32_t ssrc, av_uninit(roc);
     155             :     uint64_t index;
     156             :     int rtcp, hmac_size;
     157             : 
     158             :     // TODO: Missing replay protection
     159             : 
     160        5856 :     if (len < 2)
     161           0 :         return AVERROR_INVALIDDATA;
     162             : 
     163        5856 :     rtcp = RTP_PT_IS_RTCP(buf[1]);
     164        5856 :     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
     165             : 
     166        5856 :     if (len < hmac_size)
     167           0 :         return AVERROR_INVALIDDATA;
     168             : 
     169             :     // Authentication HMAC
     170        5856 :     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
     171             :     // If MKI is used, this should exclude the MKI as well
     172        5856 :     av_hmac_update(s->hmac, buf, len - hmac_size);
     173             : 
     174        5856 :     if (!rtcp) {
     175        5856 :         int seq = AV_RB16(buf + 2);
     176             :         uint32_t v;
     177             :         uint8_t rocbuf[4];
     178             : 
     179             :         // RFC 3711 section 3.3.1, appendix A
     180        5856 :         seq_largest = s->seq_initialized ? s->seq_largest : seq;
     181        5856 :         v = roc = s->roc;
     182        5856 :         if (seq_largest < 32768) {
     183        5856 :             if (seq - seq_largest > 32768)
     184           0 :                 v = roc - 1;
     185             :         } else {
     186           0 :             if (seq_largest - 32768 > seq)
     187           0 :                 v = roc + 1;
     188             :         }
     189        5856 :         if (v == roc) {
     190        5856 :             seq_largest = FFMAX(seq_largest, seq);
     191           0 :         } else if (v == roc + 1) {
     192           0 :             seq_largest = seq;
     193           0 :             roc = v;
     194             :         }
     195        5856 :         index = seq + (((uint64_t)v) << 16);
     196             : 
     197        5856 :         AV_WB32(rocbuf, roc);
     198        5856 :         av_hmac_update(s->hmac, rocbuf, 4);
     199             :     }
     200             : 
     201        5856 :     av_hmac_final(s->hmac, hmac, sizeof(hmac));
     202        5856 :     if (memcmp(hmac, buf + len - hmac_size, hmac_size)) {
     203           0 :         av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n");
     204           0 :         return AVERROR_INVALIDDATA;
     205             :     }
     206             : 
     207        5856 :     len -= hmac_size;
     208        5856 :     *lenptr = len;
     209             : 
     210        5856 :     if (len < 12)
     211           0 :         return AVERROR_INVALIDDATA;
     212             : 
     213        5856 :     if (rtcp) {
     214           0 :         uint32_t srtcp_index = AV_RB32(buf + len - 4);
     215           0 :         len -= 4;
     216           0 :         *lenptr = len;
     217             : 
     218           0 :         ssrc = AV_RB32(buf + 4);
     219           0 :         index = srtcp_index & 0x7fffffff;
     220             : 
     221           0 :         buf += 8;
     222           0 :         len -= 8;
     223           0 :         if (!(srtcp_index & 0x80000000))
     224           0 :             return 0;
     225             :     } else {
     226             :         int ext, csrc;
     227        5856 :         s->seq_initialized = 1;
     228        5856 :         s->seq_largest     = seq_largest;
     229        5856 :         s->roc             = roc;
     230             : 
     231        5856 :         csrc = buf[0] & 0x0f;
     232        5856 :         ext  = buf[0] & 0x10;
     233        5856 :         ssrc = AV_RB32(buf + 8);
     234             : 
     235        5856 :         buf += 12;
     236        5856 :         len -= 12;
     237             : 
     238        5856 :         buf += 4 * csrc;
     239        5856 :         len -= 4 * csrc;
     240        5856 :         if (len < 0)
     241           0 :             return AVERROR_INVALIDDATA;
     242             : 
     243        5856 :         if (ext) {
     244        5856 :             if (len < 4)
     245           0 :                 return AVERROR_INVALIDDATA;
     246        5856 :             ext = (AV_RB16(buf + 2) + 1) * 4;
     247        5856 :             if (len < ext)
     248           0 :                 return AVERROR_INVALIDDATA;
     249        5856 :             len -= ext;
     250        5856 :             buf += ext;
     251             :         }
     252             :     }
     253             : 
     254        5856 :     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
     255        5856 :     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
     256        5856 :     encrypt_counter(s->aes, iv, buf, len);
     257             : 
     258        5856 :     return 0;
     259             : }
     260             : 
     261        5865 : int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len,
     262             :                     uint8_t *out, int outlen)
     263             : {
     264        5865 :     uint8_t iv[16] = { 0 }, hmac[20];
     265             :     uint64_t index;
     266             :     uint32_t ssrc;
     267             :     int rtcp, hmac_size, padding;
     268             :     uint8_t *buf;
     269             : 
     270        5865 :     if (len < 8)
     271           0 :         return AVERROR_INVALIDDATA;
     272             : 
     273        5865 :     rtcp = RTP_PT_IS_RTCP(in[1]);
     274        5865 :     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
     275        5865 :     padding = hmac_size;
     276        5865 :     if (rtcp)
     277           0 :         padding += 4; // For the RTCP index
     278             : 
     279        5865 :     if (len + padding > outlen)
     280           0 :         return 0;
     281             : 
     282        5865 :     memcpy(out, in, len);
     283        5865 :     buf = out;
     284             : 
     285        5865 :     if (rtcp) {
     286           0 :         ssrc = AV_RB32(buf + 4);
     287           0 :         index = s->rtcp_index++;
     288             : 
     289           0 :         buf += 8;
     290           0 :         len -= 8;
     291             :     } else {
     292             :         int ext, csrc;
     293        5865 :         int seq = AV_RB16(buf + 2);
     294             : 
     295        5865 :         if (len < 12)
     296           0 :             return AVERROR_INVALIDDATA;
     297             : 
     298        5865 :         ssrc = AV_RB32(buf + 8);
     299             : 
     300        5865 :         if (seq < s->seq_largest)
     301           0 :             s->roc++;
     302        5865 :         s->seq_largest = seq;
     303        5865 :         index = seq + (((uint64_t)s->roc) << 16);
     304             : 
     305        5865 :         csrc = buf[0] & 0x0f;
     306        5865 :         ext = buf[0] & 0x10;
     307             : 
     308        5865 :         buf += 12;
     309        5865 :         len -= 12;
     310             : 
     311        5865 :         buf += 4 * csrc;
     312        5865 :         len -= 4 * csrc;
     313        5865 :         if (len < 0)
     314           0 :             return AVERROR_INVALIDDATA;
     315             : 
     316        5865 :         if (ext) {
     317        5865 :             if (len < 4)
     318           0 :                 return AVERROR_INVALIDDATA;
     319        5865 :             ext = (AV_RB16(buf + 2) + 1) * 4;
     320        5865 :             if (len < ext)
     321           0 :                 return AVERROR_INVALIDDATA;
     322        5865 :             len -= ext;
     323        5865 :             buf += ext;
     324             :         }
     325             :     }
     326             : 
     327        5865 :     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
     328        5865 :     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
     329        5865 :     encrypt_counter(s->aes, iv, buf, len);
     330             : 
     331        5865 :     if (rtcp) {
     332           0 :         AV_WB32(buf + len, 0x80000000 | index);
     333           0 :         len += 4;
     334             :     }
     335             : 
     336        5865 :     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
     337        5865 :     av_hmac_update(s->hmac, out, buf + len - out);
     338        5865 :     if (!rtcp) {
     339             :         uint8_t rocbuf[4];
     340        5865 :         AV_WB32(rocbuf, s->roc);
     341        5865 :         av_hmac_update(s->hmac, rocbuf, 4);
     342             :     }
     343        5865 :     av_hmac_final(s->hmac, hmac, sizeof(hmac));
     344             : 
     345        5865 :     memcpy(buf + len, hmac, hmac_size);
     346        5865 :     len += hmac_size;
     347        5865 :     return buf + len - out;
     348             : }