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/*

 * 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 

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 */