libavformat/srtp.c - nest-android-app/ffmpeg - Git at Google

 /*
  * SRTP encryption/decryption
  * Copyright (c) 2012 Martin Storsjo
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */

 #include "libavutil/base64.h"
 #include "libavutil/aes.h"
 #include "libavutil/hmac.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/log.h"
 #include "rtp.h"
 #include "rtpdec.h"
 #include "srtp.h"

 void ff_srtp_free(struct SRTPContext *s)
 {
     if (!s)
         return;
     av_freep(&s->aes);
     if (s->hmac)
         av_hmac_free(s->hmac);
     s->hmac = NULL;
 }

 static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf,
                             int outlen)
 {
     int i, j, outpos;
     for (i = 0, outpos = 0; outpos < outlen; i++) {
         uint8_t keystream[16];
         AV_WB16(&iv[14], i);
         av_aes_crypt(aes, keystream, iv, 1, NULL, 0);
         for (j = 0; j < 16 && outpos < outlen; j++, outpos++)
             outbuf[outpos] ^= keystream[j];
     }
 }

 static void derive_key(struct AVAES *aes, const uint8_t *salt, int label,
                        uint8_t *out, int outlen)
 {
     uint8_t input[16] = { 0 };
     memcpy(input, salt, 14);
     // Key derivation rate assumed to be zero
     input[14 - 7] ^= label;
     memset(out, 0, outlen);
     encrypt_counter(aes, input, out, outlen);
 }

 int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite,
                        const char *params)
 {
     uint8_t buf[30];

     ff_srtp_free(s);

     // RFC 4568
     if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") ||
         !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) {
         s->rtp_hmac_size = s->rtcp_hmac_size = 10;
     } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
         s->rtp_hmac_size = s->rtcp_hmac_size = 4;
     } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) {
         // RFC 5764 section 4.1.2
         s->rtp_hmac_size  = 4;
         s->rtcp_hmac_size = 10;
     } else {
         av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n",
                                      suite);
         return AVERROR(EINVAL);
     }
     if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) {
         av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n");
         return AVERROR(EINVAL);
     }
     // MKI and lifetime not handled yet
     s->aes  = av_aes_alloc();
     s->hmac = av_hmac_alloc(AV_HMAC_SHA1);
     if (!s->aes || !s->hmac)
         return AVERROR(ENOMEM);
     memcpy(s->master_key, buf, 16);
     memcpy(s->master_salt, buf + 16, 14);

     // RFC 3711
     av_aes_init(s->aes, s->master_key, 128, 0);

     derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key));
     derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt));
     derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth));

     derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key));
     derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt));
     derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth));
     return 0;
 }

 static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index,
                       uint32_t ssrc)
 {
     uint8_t indexbuf[8];
     int i;
     memset(iv, 0, 16);
     AV_WB32(&iv[4], ssrc);
     AV_WB64(indexbuf, index);
     for (i = 0; i < 8; i++) // index << 16
         iv[6 + i] ^= indexbuf[i];
     for (i = 0; i < 14; i++)
         iv[i] ^= salt[i];
 }

 int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr)
 {
     uint8_t iv[16] = { 0 }, hmac[20];
     int len = *lenptr;
     int av_uninit(seq_largest);
     uint32_t ssrc, av_uninit(roc);
     uint64_t index;
     int rtcp, hmac_size;

     // TODO: Missing replay protection

     if (len < 2)
         return AVERROR_INVALIDDATA;

     rtcp = RTP_PT_IS_RTCP(buf[1]);
     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;

     if (len < hmac_size)
         return AVERROR_INVALIDDATA;

     // Authentication HMAC
     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
     // If MKI is used, this should exclude the MKI as well
     av_hmac_update(s->hmac, buf, len - hmac_size);

     if (!rtcp) {
         int seq = AV_RB16(buf + 2);
         uint32_t v;
         uint8_t rocbuf[4];

         // RFC 3711 section 3.3.1, appendix A
         seq_largest = s->seq_initialized ? s->seq_largest : seq;
         v = roc = s->roc;
         if (seq_largest < 32768) {
             if (seq - seq_largest > 32768)
                 v = roc - 1;
         } else {
             if (seq_largest - 32768 > seq)
                 v = roc + 1;
         }
         if (v == roc) {
             seq_largest = FFMAX(seq_largest, seq);
         } else if (v == roc + 1) {
             seq_largest = seq;
             roc = v;
         }
         index = seq + (((uint64_t)v) << 16);

         AV_WB32(rocbuf, roc);
         av_hmac_update(s->hmac, rocbuf, 4);
     }

     av_hmac_final(s->hmac, hmac, sizeof(hmac));
     if (memcmp(hmac, buf + len - hmac_size, hmac_size)) {
         av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n");
         return AVERROR_INVALIDDATA;
     }

     len -= hmac_size;
     *lenptr = len;

     if (len < 12)
         return AVERROR_INVALIDDATA;

     if (rtcp) {
         uint32_t srtcp_index = AV_RB32(buf + len - 4);
         len -= 4;
         *lenptr = len;

         ssrc = AV_RB32(buf + 4);
         index = srtcp_index & 0x7fffffff;

         buf += 8;
         len -= 8;
         if (!(srtcp_index & 0x80000000))
             return 0;
     } else {
         int ext, csrc;
         s->seq_initialized = 1;
         s->seq_largest     = seq_largest;
         s->roc             = roc;

         csrc = buf[0] & 0x0f;
         ext  = buf[0] & 0x10;
         ssrc = AV_RB32(buf + 8);

         buf += 12;
         len -= 12;

         buf += 4 * csrc;
         len -= 4 * csrc;
         if (len < 0)
             return AVERROR_INVALIDDATA;

         if (ext) {
             if (len < 4)
                 return AVERROR_INVALIDDATA;
             ext = (AV_RB16(buf + 2) + 1) * 4;
             if (len < ext)
                 return AVERROR_INVALIDDATA;
             len -= ext;
             buf += ext;
         }
     }

     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
     encrypt_counter(s->aes, iv, buf, len);

     return 0;
 }

 int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len,
                     uint8_t *out, int outlen)
 {
     uint8_t iv[16] = { 0 }, hmac[20];
     uint64_t index;
     uint32_t ssrc;
     int rtcp, hmac_size, padding;
     uint8_t *buf;

     if (len < 8)
         return AVERROR_INVALIDDATA;

     rtcp = RTP_PT_IS_RTCP(in[1]);
     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
     padding = hmac_size;
     if (rtcp)
         padding += 4; // For the RTCP index

     if (len + padding > outlen)
         return 0;

     memcpy(out, in, len);
     buf = out;

     if (rtcp) {
         ssrc = AV_RB32(buf + 4);
         index = s->rtcp_index++;

         buf += 8;
         len -= 8;
     } else {
         int ext, csrc;
         int seq = AV_RB16(buf + 2);

         if (len < 12)
             return AVERROR_INVALIDDATA;

         ssrc = AV_RB32(buf + 8);

         if (seq < s->seq_largest)
             s->roc++;
         s->seq_largest = seq;
         index = seq + (((uint64_t)s->roc) << 16);

         csrc = buf[0] & 0x0f;
         ext = buf[0] & 0x10;

         buf += 12;
         len -= 12;

         buf += 4 * csrc;
         len -= 4 * csrc;
         if (len < 0)
             return AVERROR_INVALIDDATA;

         if (ext) {
             if (len < 4)
                 return AVERROR_INVALIDDATA;
             ext = (AV_RB16(buf + 2) + 1) * 4;
             if (len < ext)
                 return AVERROR_INVALIDDATA;
             len -= ext;
             buf += ext;
         }
     }

     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
     encrypt_counter(s->aes, iv, buf, len);

     if (rtcp) {
         AV_WB32(buf + len, 0x80000000 | index);
         len += 4;
     }

     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
     av_hmac_update(s->hmac, out, buf + len - out);
     if (!rtcp) {
         uint8_t rocbuf[4];
         AV_WB32(rocbuf, s->roc);
         av_hmac_update(s->hmac, rocbuf, 4);
     }
     av_hmac_final(s->hmac, hmac, sizeof(hmac));

     memcpy(buf + len, hmac, hmac_size);
     len += hmac_size;
     return buf + len - out;
 }

 #ifdef TEST
 #include <stdio.h>

 static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

 static const uint8_t rtp_aes128_80[] = {
     // RTP header
     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0x62, 0x69, 0x76, 0xca, 0xc5,
     // HMAC
     0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99,
 };

 static const uint8_t rtcp_aes128_80[] = {
     // RTCP header
     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda,
     0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35,
     // RTCP index
     0x80, 0x00, 0x00, 0x03,
     // HMAC
     0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde,
 };

 static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

 static const uint8_t rtp_aes128_32[] = {
     // RTP header
     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0x62, 0x69, 0x76, 0xca, 0xc5,
     // HMAC
     0xa1, 0xac, 0x1b, 0xb4,
 };

 static const uint8_t rtcp_aes128_32[] = {
     // RTCP header
     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b,
     0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34,
     // RTCP index
     0x80, 0x00, 0x00, 0x04,
     // HMAC
     0x5b, 0xd2, 0xa9, 0x9d,
 };

 static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

 static const uint8_t rtp_aes128_80_32[] = {
     // RTP header
     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0x62, 0x69, 0x76, 0xca, 0xc5,
     // HMAC
     0xa1, 0xac, 0x1b, 0xb4,
 };

 static const uint8_t rtcp_aes128_80_32[] = {
     // RTCP header
     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
     // encrypted payload
     0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53,
     0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9,
     // RTCP index
     0x80, 0x00, 0x00, 0x05,
     // HMAC
     0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10,
 };

 static void print_data(const uint8_t *buf, int len)
 {
     int i;
     for (i = 0; i < len; i++)
         printf("%02x", buf[i]);
     printf("\n");
 }

 static int test_decrypt(struct SRTPContext *srtp, const uint8_t *in, int len,
                         uint8_t *out)
 {
     memcpy(out, in, len);
     if (!ff_srtp_decrypt(srtp, out, &len)) {
         print_data(out, len);
         return len;
     } else
         return -1;
 }

 static void test_encrypt(const uint8_t *data, int in_len, const char *suite,
                          const char *key)
 {
     struct SRTPContext enc = { 0 }, dec = { 0 };
     int len;
     char buf[RTP_MAX_PACKET_LENGTH];
     ff_srtp_set_crypto(&enc, suite, key);
     ff_srtp_set_crypto(&dec, suite, key);
     len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf));
     if (!ff_srtp_decrypt(&dec, buf, &len)) {
         if (len == in_len && !memcmp(buf, data, len))
             printf("Decrypted content matches input\n");
         else
             printf("Decrypted content doesn't match input\n");
     } else {
         printf("Decryption failed\n");
     }
     ff_srtp_free(&enc);
     ff_srtp_free(&dec);
 }

 int main(void)
 {
     static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80";
     static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32";
     static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32";
     static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD";
     uint8_t buf[RTP_MAX_PACKET_LENGTH];
     struct SRTPContext srtp = { 0 };
     int len;
     ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key);
     len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf);
     test_encrypt(buf, len, aes128_80_suite, test_key);
     test_encrypt(buf, len, aes128_32_suite, test_key);
     test_encrypt(buf, len, aes128_80_32_suite, test_key);
     test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf);
     test_encrypt(buf, len, aes128_80_suite, test_key);
     test_encrypt(buf, len, aes128_32_suite, test_key);
     test_encrypt(buf, len, aes128_80_32_suite, test_key);
     ff_srtp_free(&srtp);

     memset(&srtp, 0, sizeof(srtp)); // Clear the context
     ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key);
     test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf);
     test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf);
     ff_srtp_free(&srtp);

     memset(&srtp, 0, sizeof(srtp)); // Clear the context
     ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key);
     test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf);
     test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf);
     ff_srtp_free(&srtp);
     return 0;
 }
 #endif /* TEST */
	/*
	* SRTP encryption/decryption
	* Copyright (c) 2012 Martin Storsjo
	*
	* This file is part of FFmpeg.
	*
	* FFmpeg is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* FFmpeg is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with FFmpeg; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	#include "libavutil/base64.h"
	#include "libavutil/aes.h"
	#include "libavutil/hmac.h"
	#include "libavutil/intreadwrite.h"
	#include "libavutil/log.h"
	#include "rtp.h"
	#include "rtpdec.h"
	#include "srtp.h"

	void ff_srtp_free(struct SRTPContext *s)
	{
	if (!s)
	return;
	av_freep(&s->aes);
	if (s->hmac)
	av_hmac_free(s->hmac);
	s->hmac = NULL;
	}

	static void encrypt_counter(struct AVAES aes, uint8_t iv, uint8_t *outbuf,
	int outlen)
	{
	int i, j, outpos;
	for (i = 0, outpos = 0; outpos < outlen; i++) {
	uint8_t keystream[16];
	AV_WB16(&iv[14], i);
	av_aes_crypt(aes, keystream, iv, 1, NULL, 0);
	for (j = 0; j < 16 && outpos < outlen; j++, outpos++)
	outbuf[outpos] ^= keystream[j];
	}
	}

	static void derive_key(struct AVAES aes, const uint8_t salt, int label,
	uint8_t *out, int outlen)
	{
	uint8_t input[16] = { 0 };
	memcpy(input, salt, 14);
	// Key derivation rate assumed to be zero
	input[14 - 7] ^= label;
	memset(out, 0, outlen);
	encrypt_counter(aes, input, out, outlen);
	}

	int ff_srtp_set_crypto(struct SRTPContext s, const char suite,
	const char *params)
	{
	uint8_t buf[30];

	ff_srtp_free(s);

	// RFC 4568
	if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") \|\|
	!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) {
	s->rtp_hmac_size = s->rtcp_hmac_size = 10;
	} else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
	s->rtp_hmac_size = s->rtcp_hmac_size = 4;
	} else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) {
	// RFC 5764 section 4.1.2
	s->rtp_hmac_size = 4;
	s->rtcp_hmac_size = 10;
	} else {
	av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n",
	suite);
	return AVERROR(EINVAL);
	}
	if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) {
	av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n");
	return AVERROR(EINVAL);
	}
	// MKI and lifetime not handled yet
	s->aes = av_aes_alloc();
	s->hmac = av_hmac_alloc(AV_HMAC_SHA1);
	if (!s->aes \|\| !s->hmac)
	return AVERROR(ENOMEM);
	memcpy(s->master_key, buf, 16);
	memcpy(s->master_salt, buf + 16, 14);

	// RFC 3711
	av_aes_init(s->aes, s->master_key, 128, 0);

	derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key));
	derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt));
	derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth));

	derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key));
	derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt));
	derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth));
	return 0;
	}

	static void create_iv(uint8_t iv, const uint8_t salt, uint64_t index,
	uint32_t ssrc)
	{
	uint8_t indexbuf[8];
	int i;
	memset(iv, 0, 16);
	AV_WB32(&iv[4], ssrc);
	AV_WB64(indexbuf, index);
	for (i = 0; i < 8; i++) // index << 16
	iv[6 + i] ^= indexbuf[i];
	for (i = 0; i < 14; i++)
	iv[i] ^= salt[i];
	}

	int ff_srtp_decrypt(struct SRTPContext s, uint8_t buf, int *lenptr)
	{
	uint8_t iv[16] = { 0 }, hmac[20];
	int len = *lenptr;
	int av_uninit(seq_largest);
	uint32_t ssrc, av_uninit(roc);
	uint64_t index;
	int rtcp, hmac_size;

	// TODO: Missing replay protection

	if (len < 2)
	return AVERROR_INVALIDDATA;

	rtcp = RTP_PT_IS_RTCP(buf[1]);
	hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;

	if (len < hmac_size)
	return AVERROR_INVALIDDATA;

	// Authentication HMAC
	av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
	// If MKI is used, this should exclude the MKI as well
	av_hmac_update(s->hmac, buf, len - hmac_size);

	if (!rtcp) {
	int seq = AV_RB16(buf + 2);
	uint32_t v;
	uint8_t rocbuf[4];

	// RFC 3711 section 3.3.1, appendix A
	seq_largest = s->seq_initialized ? s->seq_largest : seq;
	v = roc = s->roc;
	if (seq_largest < 32768) {
	if (seq - seq_largest > 32768)
	v = roc - 1;
	} else {
	if (seq_largest - 32768 > seq)
	v = roc + 1;
	}
	if (v == roc) {
	seq_largest = FFMAX(seq_largest, seq);
	} else if (v == roc + 1) {
	seq_largest = seq;
	roc = v;
	}
	index = seq + (((uint64_t)v) << 16);

	AV_WB32(rocbuf, roc);
	av_hmac_update(s->hmac, rocbuf, 4);
	}

	av_hmac_final(s->hmac, hmac, sizeof(hmac));
	if (memcmp(hmac, buf + len - hmac_size, hmac_size)) {
	av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n");
	return AVERROR_INVALIDDATA;
	}

	len -= hmac_size;
	*lenptr = len;

	if (len < 12)
	return AVERROR_INVALIDDATA;

	if (rtcp) {
	uint32_t srtcp_index = AV_RB32(buf + len - 4);
	len -= 4;
	*lenptr = len;

	ssrc = AV_RB32(buf + 4);
	index = srtcp_index & 0x7fffffff;

	buf += 8;
	len -= 8;
	if (!(srtcp_index & 0x80000000))
	return 0;
	} else {
	int ext, csrc;
	s->seq_initialized = 1;
	s->seq_largest = seq_largest;
	s->roc = roc;

	csrc = buf[0] & 0x0f;
	ext = buf[0] & 0x10;
	ssrc = AV_RB32(buf + 8);

	buf += 12;
	len -= 12;

	buf += 4 * csrc;
	len -= 4 * csrc;
	if (len < 0)
	return AVERROR_INVALIDDATA;

	if (ext) {
	if (len < 4)
	return AVERROR_INVALIDDATA;
	ext = (AV_RB16(buf + 2) + 1) * 4;
	if (len < ext)
	return AVERROR_INVALIDDATA;
	len -= ext;
	buf += ext;
	}
	}

	create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
	av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
	encrypt_counter(s->aes, iv, buf, len);

	return 0;
	}

	int ff_srtp_encrypt(struct SRTPContext s, const uint8_t in, int len,
	uint8_t *out, int outlen)
	{
	uint8_t iv[16] = { 0 }, hmac[20];
	uint64_t index;
	uint32_t ssrc;
	int rtcp, hmac_size, padding;
	uint8_t *buf;

	if (len < 8)
	return AVERROR_INVALIDDATA;

	rtcp = RTP_PT_IS_RTCP(in[1]);
	hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
	padding = hmac_size;
	if (rtcp)
	padding += 4; // For the RTCP index

	if (len + padding > outlen)
	return 0;

	memcpy(out, in, len);
	buf = out;

	if (rtcp) {
	ssrc = AV_RB32(buf + 4);
	index = s->rtcp_index++;

	buf += 8;
	len -= 8;
	} else {
	int ext, csrc;
	int seq = AV_RB16(buf + 2);

	if (len < 12)
	return AVERROR_INVALIDDATA;

	ssrc = AV_RB32(buf + 8);

	if (seq < s->seq_largest)
	s->roc++;
	s->seq_largest = seq;
	index = seq + (((uint64_t)s->roc) << 16);

	csrc = buf[0] & 0x0f;
	ext = buf[0] & 0x10;

	buf += 12;
	len -= 12;

	buf += 4 * csrc;
	len -= 4 * csrc;
	if (len < 0)
	return AVERROR_INVALIDDATA;

	if (ext) {
	if (len < 4)
	return AVERROR_INVALIDDATA;
	ext = (AV_RB16(buf + 2) + 1) * 4;
	if (len < ext)
	return AVERROR_INVALIDDATA;
	len -= ext;
	buf += ext;
	}
	}

	create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
	av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
	encrypt_counter(s->aes, iv, buf, len);

	if (rtcp) {
	AV_WB32(buf + len, 0x80000000 \| index);
	len += 4;
	}

	av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
	av_hmac_update(s->hmac, out, buf + len - out);
	if (!rtcp) {
	uint8_t rocbuf[4];
	AV_WB32(rocbuf, s->roc);
	av_hmac_update(s->hmac, rocbuf, 4);
	}
	av_hmac_final(s->hmac, hmac, sizeof(hmac));

	memcpy(buf + len, hmac, hmac_size);
	len += hmac_size;
	return buf + len - out;
	}

	#ifdef TEST
	#include <stdio.h>

	static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

	static const uint8_t rtp_aes128_80[] = {
	// RTP header
	0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0x62, 0x69, 0x76, 0xca, 0xc5,
	// HMAC
	0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99,
	};

	static const uint8_t rtcp_aes128_80[] = {
	// RTCP header
	0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda,
	0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35,
	// RTCP index
	0x80, 0x00, 0x00, 0x03,
	// HMAC
	0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde,
	};

	static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

	static const uint8_t rtp_aes128_32[] = {
	// RTP header
	0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0x62, 0x69, 0x76, 0xca, 0xc5,
	// HMAC
	0xa1, 0xac, 0x1b, 0xb4,
	};

	static const uint8_t rtcp_aes128_32[] = {
	// RTCP header
	0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b,
	0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34,
	// RTCP index
	0x80, 0x00, 0x00, 0x04,
	// HMAC
	0x5b, 0xd2, 0xa9, 0x9d,
	};

	static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

	static const uint8_t rtp_aes128_80_32[] = {
	// RTP header
	0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0x62, 0x69, 0x76, 0xca, 0xc5,
	// HMAC
	0xa1, 0xac, 0x1b, 0xb4,
	};

	static const uint8_t rtcp_aes128_80_32[] = {
	// RTCP header
	0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
	// encrypted payload
	0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53,
	0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9,
	// RTCP index
	0x80, 0x00, 0x00, 0x05,
	// HMAC
	0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10,
	};

	static void print_data(const uint8_t *buf, int len)
	{
	int i;
	for (i = 0; i < len; i++)
	printf("%02x", buf[i]);
	printf("\n");
	}

	static int test_decrypt(struct SRTPContext srtp, const uint8_t in, int len,
	uint8_t *out)
	{
	memcpy(out, in, len);
	if (!ff_srtp_decrypt(srtp, out, &len)) {
	print_data(out, len);
	return len;
	} else
	return -1;
	}

	static void test_encrypt(const uint8_t data, int in_len, const char suite,
	const char *key)
	{
	struct SRTPContext enc = { 0 }, dec = { 0 };
	int len;
	char buf[RTP_MAX_PACKET_LENGTH];
	ff_srtp_set_crypto(&enc, suite, key);
	ff_srtp_set_crypto(&dec, suite, key);
	len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf));
	if (!ff_srtp_decrypt(&dec, buf, &len)) {
	if (len == in_len && !memcmp(buf, data, len))
	printf("Decrypted content matches input\n");
	else
	printf("Decrypted content doesn't match input\n");
	} else {
	printf("Decryption failed\n");
	}
	ff_srtp_free(&enc);
	ff_srtp_free(&dec);
	}

	int main(void)
	{
	static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80";
	static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32";
	static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32";
	static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD";
	uint8_t buf[RTP_MAX_PACKET_LENGTH];
	struct SRTPContext srtp = { 0 };
	int len;
	ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key);
	len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf);
	test_encrypt(buf, len, aes128_80_suite, test_key);
	test_encrypt(buf, len, aes128_32_suite, test_key);
	test_encrypt(buf, len, aes128_80_32_suite, test_key);
	test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf);
	test_encrypt(buf, len, aes128_80_suite, test_key);
	test_encrypt(buf, len, aes128_32_suite, test_key);
	test_encrypt(buf, len, aes128_80_32_suite, test_key);
	ff_srtp_free(&srtp);

	memset(&srtp, 0, sizeof(srtp)); // Clear the context
	ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key);
	test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf);
	test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf);
	ff_srtp_free(&srtp);

	memset(&srtp, 0, sizeof(srtp)); // Clear the context
	ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key);
	test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf);
	test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf);
	ff_srtp_free(&srtp);
	return 0;
	}
	#endif /* TEST */