/*
  * 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;
 }