Move SRTP implementation into crypto library for reuse

1 files changed, 0 insertions, 836 deletions

diff --git a/plugins/rtp/src/srtp.c b/plugins/rtp/src/srtp.c
deleted file mode 100644
index 708244d9..00000000
--- a/plugins/rtp/src/srtp.c
+++ /dev/null
@@ -1,836 +0,0 @@
-/*
- * Secure RTP with libgcrypt
- * Copyright (C) 2007  Rémi Denis-Courmont
- *
- * This library 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.
- *
- * This library 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 this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
- */
-
-/* TODO:
- * Useless stuff (because nothing depends on it):
- * - non-nul key derivation rate
- * - MKI payload
- */
-
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
-#include <stdint.h>
-#include <stddef.h>
-
-#include "srtp.h"
-
-#include <stdbool.h>
-#include <stdlib.h>
-#include <assert.h>
-#include <errno.h>
-
-#include <gcrypt.h>
-
-#ifdef _WIN32
-# include <winsock2.h>
-#else
-# include <netinet/in.h>
-#endif
-
-#define debug( ... ) (void)0
-
-typedef struct srtp_proto_t
-{
-    gcry_cipher_hd_t cipher;
-    gcry_md_hd_t     mac;
-    uint64_t         window;
-    uint32_t         salt[4];
-} srtp_proto_t;
-
-struct srtp_session_t
-{
-    srtp_proto_t rtp;
-    srtp_proto_t rtcp;
-    unsigned flags;
-    unsigned kdr;
-    uint32_t rtcp_index;
-    uint32_t rtp_roc;
-    uint16_t rtp_seq;
-    uint16_t rtp_rcc;
-    uint8_t  tag_len;
-};
-
-enum
-{
-    SRTP_CRYPT,
-    SRTP_AUTH,
-    SRTP_SALT,
-    SRTCP_CRYPT,
-    SRTCP_AUTH,
-    SRTCP_SALT
-};
-
-
-static inline unsigned rcc_mode (const srtp_session_t *s)
-{
-    return (s->flags >> 4) & 3;
-}
-
-
-static void proto_destroy (srtp_proto_t *p)
-{
-    gcry_md_close (p->mac);
-    gcry_cipher_close (p->cipher);
-}
-
-
-/**
- * Releases all resources associated with a Secure RTP session.
- */
-void srtp_destroy (srtp_session_t *s)
-{
-    assert (s != NULL);
-
-    proto_destroy (&s->rtcp);
-    proto_destroy (&s->rtp);
-    free (s);
-}
-
-
-static int proto_create (srtp_proto_t *p, int gcipher, int gmd)
-{
-    if (gcry_cipher_open (&p->cipher, gcipher, GCRY_CIPHER_MODE_CTR, 0) == 0)
-    {
-        if (gcry_md_open (&p->mac, gmd, GCRY_MD_FLAG_HMAC) == 0)
-            return 0;
-        gcry_cipher_close (p->cipher);
-    }
-    return -1;
-}
-
-
-/**
- * Allocates a Secure RTP one-way session.
- * The same session cannot be used both ways because this would confuse
- * internal cryptographic counters; it is however of course feasible to open
- * multiple simultaneous sessions with the same master key.
- *
- * @param encr encryption algorithm number
- * @param auth authentication algortihm number
- * @param tag_len authentication tag byte length (NOT including RCC)
- * @param flags OR'ed optional flags.
- *
- * @return NULL in case of error
- */
-srtp_session_t *
-srtp_create (int encr, int auth, unsigned tag_len, int prf, unsigned flags)
-{
-    if ((flags & ~SRTP_FLAGS_MASK))
-        return NULL;
-
-    int cipher, md;
-    switch (encr)
-    {
-        case SRTP_ENCR_NULL:
-            cipher = GCRY_CIPHER_NONE;
-            break;
-
-        case SRTP_ENCR_AES_CM:
-            cipher = GCRY_CIPHER_AES;
-            break;
-
-        default:
-            return NULL;
-    }
-
-    switch (auth)
-    {
-        case SRTP_AUTH_NULL:
-            md = GCRY_MD_NONE;
-            break;
-
-        case SRTP_AUTH_HMAC_SHA1:
-            md = GCRY_MD_SHA1;
-            break;
-
-        default:
-            return NULL;
-    }
-
-    if (tag_len > gcry_md_get_algo_dlen (md))
-        return NULL;
-
-    if (prf != SRTP_PRF_AES_CM)
-        return NULL;
-
-    srtp_session_t *s = malloc (sizeof (*s));
-    if (s == NULL)
-        return NULL;
-
-    memset (s, 0, sizeof (*s));
-    s->flags = flags;
-    s->tag_len = tag_len;
-    s->rtp_rcc = 1; /* Default RCC rate */
-    if (rcc_mode (s))
-    {
-        if (tag_len < 4)
-            goto error;
-    }
-
-    if (proto_create (&s->rtp, cipher, md) == 0)
-    {
-        if (proto_create (&s->rtcp, cipher, md) == 0)
-            return s;
-        proto_destroy (&s->rtp);
-    }
-
-    error:
-    free (s);
-    return NULL;
-}
-
-
-/**
- * Counter Mode encryption/decryption (ctr length = 16 bytes)
- * with non-padded (truncated) text
- */
-static int
-do_ctr_crypt (gcry_cipher_hd_t hd, const void *ctr, uint8_t *data, size_t len)
-{
-    const size_t ctrlen = 16;
-    div_t d = div (len, ctrlen);
-
-    if (gcry_cipher_setctr (hd, ctr, ctrlen)
-        || gcry_cipher_encrypt (hd, data, d.quot * ctrlen, NULL, 0))
-        return -1;
-
-    if (d.rem)
-    {
-        /* Truncated last block */
-        uint8_t dummy[ctrlen];
-        data += d.quot * ctrlen;
-        memcpy (dummy, data, d.rem);
-        memset (dummy + d.rem, 0, ctrlen - d.rem);
-
-        if (gcry_cipher_encrypt (hd, dummy, ctrlen, data, ctrlen))
-            return -1;
-        memcpy (data, dummy, d.rem);
-    }
-
-    return 0;
-}
-
-
-/**
- * AES-CM key derivation (saltlen = 14 bytes)
- */
-static int
-do_derive (gcry_cipher_hd_t prf, const void *salt,
-           const uint8_t *r, size_t rlen, uint8_t label,
-           void *out, size_t outlen)
-{
-    uint8_t iv[16];
-
-    memcpy (iv, salt, 14);
-    iv[14] = iv[15] = 0;
-
-    assert (rlen < 14);
-    iv[13 - rlen] ^= label;
-    for (size_t i = 0; i < rlen; i++)
-        iv[sizeof (iv) - rlen + i] ^= r[i];
-
-    memset (out, 0, outlen);
-    return do_ctr_crypt (prf, iv, out, outlen);
-}
-
-
-/**
- * Sets (or resets) the master key and master salt for a SRTP session.
- * This must be done at least once before using srtp_send(), srtp_recv(),
- * srtcp_send() or srtcp_recv(). Also, rekeying is required every
- * 2^48 RTP packets or 2^31 RTCP packets (whichever comes first),
- * otherwise the protocol security might be broken.
- *
- * @return 0 on success, in case of error:
- *  EINVAL  invalid or unsupported key/salt sizes combination
- */
-int
-srtp_setkey (srtp_session_t *s, const void *key, size_t keylen,
-             const void *salt, size_t saltlen)
-{
-    /* SRTP/SRTCP cipher/salt/MAC keys derivation */
-    gcry_cipher_hd_t prf;
-    uint8_t r[6], keybuf[20];
-
-    if (saltlen != 14)
-        return EINVAL;
-
-    if (gcry_cipher_open (&prf, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CTR, 0)
-        || gcry_cipher_setkey (prf, key, keylen))
-        return EINVAL;
-
-    /* SRTP key derivation */
-#if 0
-    if (s->kdr != 0)
-    {
-        uint64_t index = (((uint64_t)s->rtp_roc) << 16) | s->rtp_seq;
-        index /= s->kdr;
-
-        for (int i = sizeof (r) - 1; i >= 0; i--)
-        {
-            r[i] = index & 0xff;
-            index = index >> 8;
-        }
-    }
-    else
-#endif
-    memset (r, 0, sizeof (r));
-    if (do_derive (prf, salt, r, 6, SRTP_CRYPT, keybuf, 16)
-        || gcry_cipher_setkey (s->rtp.cipher, keybuf, 16)
-        || do_derive (prf, salt, r, 6, SRTP_AUTH, keybuf, 20)
-        || gcry_md_setkey (s->rtp.mac, keybuf, 20)
-        || do_derive (prf, salt, r, 6, SRTP_SALT, s->rtp.salt, 14))
-        return -1;
-
-    /* SRTCP key derivation */
-    memcpy (r, &(uint32_t){ htonl (s->rtcp_index) }, 4);
-    if (do_derive (prf, salt, r, 4, SRTCP_CRYPT, keybuf, 16)
-        || gcry_cipher_setkey (s->rtcp.cipher, keybuf, 16)
-        || do_derive (prf, salt, r, 4, SRTCP_AUTH, keybuf, 20)
-        || gcry_md_setkey (s->rtcp.mac, keybuf, 20)
-        || do_derive (prf, salt, r, 4, SRTCP_SALT, s->rtcp.salt, 14))
-        return -1;
-
-    (void)gcry_cipher_close (prf);
-    return 0;
-}
-
-static int hexdigit (char c)
-{
-    if ((c >= '0') && (c <= '9'))
-        return c - '0';
-    if ((c >= 'A') && (c <= 'F'))
-        return c - 'A' + 0xA;
-    if ((c >= 'a') && (c <= 'f'))
-        return c - 'a' + 0xa;
-    return -1;
-}
-
-static ssize_t hexstring (const char *in, uint8_t *out, size_t outlen)
-{
-    size_t inlen = strlen (in);
-
-    if ((inlen > (2 * outlen)) || (inlen & 1))
-        return -1;
-
-    for (size_t i = 0; i < inlen; i += 2)
-    {
-        int a = hexdigit (in[i]), b = hexdigit (in[i + 1]);
-        if ((a == -1) || (b == -1))
-            return -1;
-        out[i / 2] = (a << 4) | b;
-    }
-    return inlen / 2;
-}
-
-/**
- * Sets (or resets) the master key and master salt for a SRTP session
- * from hexadecimal strings. See also srtp_setkey().
- *
- * @return 0 on success, in case of error:
- *  EINVAL  invalid or unsupported key/salt sizes combination
- */
-int
-srtp_setkeystring (srtp_session_t *s, const char *key, const char *salt)
-{
-    uint8_t bkey[16]; /* TODO/NOTE: hard-coded for AES */
-    uint8_t bsalt[14]; /* TODO/NOTE: hard-coded for the PRF-AES-CM */
-    ssize_t bkeylen = hexstring (key, bkey, sizeof (bkey));
-    ssize_t bsaltlen = hexstring (salt, bsalt, sizeof (bsalt));
-
-    if ((bkeylen == -1) || (bsaltlen == -1))
-        return EINVAL;
-    return srtp_setkey (s, bkey, bkeylen, bsalt, bsaltlen) ? EINVAL : 0;
-}
-
-/**
- * Sets Roll-over-Counter Carry (RCC) rate for the SRTP session. If not
- * specified (through this function), the default rate of ONE is assumed
- * (i.e. every RTP packets will carry the RoC). RCC rate is ignored if none
- * of the RCC mode has been selected.
- *
- * The RCC mode is selected through one of these flags for srtp_create():
- *  SRTP_RCC_MODE1: integrity protection only for RoC carrying packets
- *  SRTP_RCC_MODE2: integrity protection for all packets
- *  SRTP_RCC_MODE3: no integrity protection
- *
- * RCC mode 3 is insecure. Compared to plain RTP, it provides confidentiality
- * (through encryption) but is much more prone to DoS. It can only be used if
- * anti-spoofing protection is provided by lower network layers (e.g. IPsec,
- * or trusted routers and proper source address filtering).
- *
- * If RCC rate is 1, RCC mode 1 and 2 are functionally identical.
- *
- * @param rate RoC Carry rate (MUST NOT be zero)
- */
-void srtp_setrcc_rate (srtp_session_t *s, uint16_t rate)
-{
-    assert (rate != 0);
-    s->rtp_rcc = rate;
-}
-
-
-/** AES-CM for RTP (salt = 14 bytes + 2 nul bytes) */
-static int
-rtp_crypt (gcry_cipher_hd_t hd, uint32_t ssrc, uint32_t roc, uint16_t seq,
-           const uint32_t *salt, uint8_t *data, size_t len)
-{
-    /* Determines cryptographic counter (IV) */
-    uint32_t counter[4];
-    counter[0] = salt[0];
-    counter[1] = salt[1] ^ ssrc;
-    counter[2] = salt[2] ^ htonl (roc);
-    counter[3] = salt[3] ^ htonl (seq << 16);
-
-    /* Encryption */
-    return do_ctr_crypt (hd, counter, data, len);
-}
-
-
-/** Determines SRTP Roll-Over-Counter (in host-byte order) */
-static uint32_t
-srtp_compute_roc (const srtp_session_t *s, uint16_t seq)
-{
-    uint32_t roc = s->rtp_roc;
-
-    if (((seq - s->rtp_seq) & 0xffff) < 0x8000)
-    {
-        /* Sequence is ahead, good */
-        if (seq < s->rtp_seq)
-            roc++; /* Sequence number wrap */
-    }
-    else
-    {
-        /* Sequence is late, bad */
-        if (seq > s->rtp_seq)
-            roc--; /* Wrap back */
-    }
-    return roc;
-}
-
-
-/** Returns RTP sequence (in host-byte order) */
-static inline uint16_t rtp_seq (const uint8_t *buf)
-{
-    return (buf[2] << 8) | buf[3];
-}
-
-
-/** Message Authentication and Integrity for RTP */
-static const uint8_t *
-rtp_digest (gcry_md_hd_t md, const uint8_t *data, size_t len,
-            uint32_t roc)
-{
-    gcry_md_reset (md);
-    gcry_md_write (md, data, len);
-    gcry_md_write (md, &(uint32_t){ htonl (roc) }, 4);
-    return gcry_md_read (md, 0);
-}
-
-
-/**
- * Encrypts/decrypts a RTP packet and updates SRTP context
- * (CTR block cypher mode of operation has identical encryption and
- * decryption function).
- *
- * @param buf RTP packet to be en-/decrypted
- * @param len RTP packet length
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted RTP packet
- *  EACCES  replayed packet or out-of-window or sync lost
- */
-static int srtp_crypt (srtp_session_t *s, uint8_t *buf, size_t len)
-{
-    assert (s != NULL);
-    assert (len >= 12u);
-
-    if ((buf[0] >> 6) != 2)
-        return EINVAL;
-
-    /* Computes encryption offset */
-    uint16_t offset = 12;
-    offset += (buf[0] & 0xf) * 4; // skips CSRC
-
-    if (buf[0] & 0x10)
-    {
-        uint16_t extlen;
-
-        offset += 4;
-        if (len < offset)
-            return EINVAL;
-
-        memcpy (&extlen, buf + offset - 2, 2);
-        offset += htons (extlen); // skips RTP extension header
-    }
-
-    if (len < offset)
-        return EINVAL;
-
-    /* Determines RTP 48-bits counter and SSRC */
-    uint16_t seq = rtp_seq (buf);
-    uint32_t roc = srtp_compute_roc (s, seq), ssrc;
-    memcpy (&ssrc, buf + 8, 4);
-
-    /* Updates ROC and sequence (it's safe now) */
-    int16_t diff = seq - s->rtp_seq;
-    if (diff > 0)
-    {
-        /* Sequence in the future, good */
-        s->rtp.window = s->rtp.window << diff;
-        s->rtp.window |= UINT64_C(1);
-        s->rtp_seq = seq, s->rtp_roc = roc;
-    }
-    else
-    {
-        /* Sequence in the past/present, bad */
-        diff = -diff;
-        if ((diff >= 64) || ((s->rtp.window >> diff) & 1))
-            return EACCES; /* Replay attack */
-        s->rtp.window |= UINT64_C(1) << diff;
-    }
-
-    /* Encrypt/Decrypt */
-    if (s->flags & SRTP_UNENCRYPTED)
-        return 0;
-
-    if (rtp_crypt (s->rtp.cipher, ssrc, roc, seq, s->rtp.salt,
-                   buf + offset, len - offset))
-        return EINVAL;
-
-    return 0;
-}
-
-
-/**
- * Turns a RTP packet into a SRTP packet: encrypt it, then computes
- * the authentication tag and appends it.
- * Note that you can encrypt packet in disorder.
- *
- * @param buf RTP packet to be encrypted/digested
- * @param lenp pointer to the RTP packet length on entry,
- *             set to the SRTP length on exit (undefined on non-ENOSPC error)
- * @param bufsize size (bytes) of the packet buffer
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted RTP packet or internal error
- *  ENOSPC  bufsize is too small to add authentication tag
- *          (<lenp> will hold the required byte size)
- *  EACCES  packet would trigger a replay error on receiver
- */
-int
-srtp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t bufsize)
-{
-    size_t len = *lenp;
-    size_t tag_len;
-    size_t roc_len = 0;
-
-    /* Compute required buffer size */
-    if (len < 12u)
-        return EINVAL;
-
-    if (!(s->flags & SRTP_UNAUTHENTICATED))
-    {
-        tag_len = s->tag_len;
-
-        if (rcc_mode (s))
-        {
-            assert (tag_len >= 4);
-            assert (s->rtp_rcc != 0);
-            if ((rtp_seq (buf) % s->rtp_rcc) == 0)
-            {
-                roc_len = 4;
-                if (rcc_mode (s) == 3)
-                    tag_len = 0; /* RCC mode 3 -> no auth*/
-                else
-                    tag_len -= 4; /* RCC mode 1 or 2 -> auth*/
-            }
-            else
-            {
-                if (rcc_mode (s) & 1)
-                    tag_len = 0; /* RCC mode 1 or 3 -> no auth */
-            }
-        }
-
-        *lenp = len + roc_len + tag_len;
-    }
-    else
-        tag_len = 0;
-
-    if (bufsize < *lenp)
-        return ENOSPC;
-
-    /* Encrypt payload */
-    int val = srtp_crypt (s, buf, len);
-    if (val)
-        return val;
-
-    /* Authenticate payload */
-    if (!(s->flags & SRTP_UNAUTHENTICATED))
-    {
-        uint32_t roc = srtp_compute_roc (s, rtp_seq (buf));
-        const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, roc);
-
-        if (roc_len)
-        {
-            memcpy (buf + len, &(uint32_t){ htonl (s->rtp_roc) }, 4);
-            len += 4;
-        }
-        memcpy (buf + len, tag, tag_len);
-#if 0
-        printf ("Sent    : 0x");
-        for (unsigned i = 0; i < tag_len; i++)
-            printf ("%02x", tag[i]);
-        puts ("");
-#endif
-    }
-
-    return 0;
-}
-
-
-/**
- * Turns a SRTP packet into a RTP packet: authenticates the packet,
- * then decrypts it.
- *
- * @param buf RTP packet to be digested/decrypted
- * @param lenp pointer to the SRTP packet length on entry,
- *             set to the RTP length on exit (undefined in case of error)
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted SRTP packet
- *  EACCES  authentication failed (spoofed packet or out-of-sync)
- */
-int
-srtp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp)
-{
-    size_t len = *lenp;
-    if (len < 12u)
-        return EINVAL;
-
-    if (!(s->flags & SRTP_UNAUTHENTICATED))
-    {
-        size_t tag_len = s->tag_len, roc_len = 0;
-        if (rcc_mode (s))
-        {
-            if ((rtp_seq (buf) % s->rtp_rcc) == 0)
-            {
-                roc_len = 4;
-                if (rcc_mode (s) == 3)
-                    tag_len = 0;
-                else
-                    tag_len -= 4;
-            }
-            else
-            {
-                if (rcc_mode (s) & 1)
-                    tag_len = 0; // RCC mode 1 or 3: no auth
-            }
-        }
-
-        if (len < (12u + roc_len + tag_len))
-            return EINVAL;
-        len -= roc_len + tag_len;
-
-        uint32_t roc = srtp_compute_roc (s, rtp_seq (buf)), rcc;
-        if (roc_len)
-        {
-            assert (roc_len == 4);
-            memcpy (&rcc, buf + len, 4);
-            rcc = ntohl (rcc);
-        }
-        else
-            rcc = roc;
-
-        const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, rcc);
-#if 0
-        printf ("Computed: 0x");
-        for (unsigned i = 0; i < tag_len; i++)
-            printf ("%02x", tag[i]);
-        printf ("\nReceived: 0x");
-        for (unsigned i = 0; i < tag_len; i++)
-            printf ("%02x", buf[len + roc_len + i]);
-        puts ("");
-#endif
-        if (memcmp (buf + len + roc_len, tag, tag_len))
-            return EACCES;
-
-        if (roc_len)
-        {
-            /* Authenticated packet carried a Roll-Over-Counter */
-            s->rtp_roc += rcc - roc;
-            assert (srtp_compute_roc (s, rtp_seq (buf)) == rcc);
-        }
-        *lenp = len;
-    }
-
-    return srtp_crypt (s, buf, len);
-}
-
-
-/** AES-CM for RTCP (salt = 14 bytes + 2 nul bytes) */
-static int
-rtcp_crypt (gcry_cipher_hd_t hd, uint32_t ssrc, uint32_t index,
-            const uint32_t *salt, uint8_t *data, size_t len)
-{
-    return rtp_crypt (hd, ssrc, index >> 16, index & 0xffff, salt, data, len);
-}
-
-
-/** Message Authentication and Integrity for RTCP */
-static const uint8_t *
-rtcp_digest (gcry_md_hd_t md, const void *data, size_t len)
-{
-    gcry_md_reset (md);
-    gcry_md_write (md, data, len);
-    return gcry_md_read (md, 0);
-}
-
-
-/**
- * Encrypts/decrypts a RTCP packet and updates SRTCP context
- * (CTR block cypher mode of operation has identical encryption and
- * decryption function).
- *
- * @param buf RTCP packet to be en-/decrypted
- * @param len RTCP packet length
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted RTCP packet
- */
-static int srtcp_crypt (srtp_session_t *s, uint8_t *buf, size_t len)
-{
-    assert (s != NULL);
-
-    /* 8-bytes unencrypted header, and 4-bytes unencrypted footer */
-    if ((len < 12) || ((buf[0] >> 6) != 2))
-        return EINVAL;
-
-    uint32_t index;
-    memcpy (&index, buf + len, 4);
-    index = ntohl (index);
-    if (((index >> 31) != 0) != ((s->flags & SRTCP_UNENCRYPTED) == 0))
-        return EINVAL; // E-bit mismatch
-
-    index &= ~(1 << 31); // clear E-bit for counter
-
-    /* Updates SRTCP index (safe here) */
-    int32_t diff = index - s->rtcp_index;
-    if (diff > 0)
-    {
-        /* Packet in the future, good */
-        s->rtcp.window = s->rtcp.window << diff;
-        s->rtcp.window |= UINT64_C(1);
-        s->rtcp_index = index;
-    }
-    else
-    {
-        /* Packet in the past/present, bad */
-        diff = -diff;
-        if ((diff >= 64) || ((s->rtcp.window >> diff) & 1))
-            return EACCES; // replay attack!
-        s->rtp.window |= UINT64_C(1) << diff;
-    }
-
-    /* Crypts SRTCP */
-    if (s->flags & SRTCP_UNENCRYPTED)
-        return 0;
-
-    uint32_t ssrc;
-    memcpy (&ssrc, buf + 4, 4);
-
-    if (rtcp_crypt (s->rtcp.cipher, ssrc, index, s->rtp.salt,
-                    buf + 8, len - 8))
-        return EINVAL;
-    return 0;
-}
-
-
-/**
- * Turns a RTCP packet into a SRTCP packet: encrypt it, then computes
- * the authentication tag and appends it.
- *
- * @param buf RTCP packet to be encrypted/digested
- * @param lenp pointer to the RTCP packet length on entry,
- *             set to the SRTCP length on exit (undefined in case of error)
- * @param bufsize size (bytes) of the packet buffer
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted RTCP packet or internal error
- *  ENOSPC  bufsize is too small (to add index and authentication tag)
- */
-int
-srtcp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t bufsize)
-{
-    size_t len = *lenp;
-    if (bufsize < (len + 4 + s->tag_len))
-        return ENOSPC;
-
-    uint32_t index = ++s->rtcp_index;
-    if (index >> 31)
-        s->rtcp_index = index = 0; /* 31-bit wrap */
-
-    if ((s->flags & SRTCP_UNENCRYPTED) == 0)
-        index |= 0x80000000; /* Set Encrypted bit */
-    memcpy (buf + len, &(uint32_t){ htonl (index) }, 4);
-
-    int val = srtcp_crypt (s, buf, len);
-    if (val)
-        return val;
-
-    len += 4; /* Digests SRTCP index too */
-
-    const uint8_t *tag = rtcp_digest (s->rtcp.mac, buf, len);
-    memcpy (buf + len, tag, s->tag_len);
-    *lenp = len + s->tag_len;
-    return 0;
-}
-
-
-/**
- * Turns a SRTCP packet into a RTCP packet: authenticates the packet,
- * then decrypts it.
- *
- * @param buf RTCP packet to be digested/decrypted
- * @param lenp pointer to the SRTCP packet length on entry,
- *             set to the RTCP length on exit (undefined in case of error)
- *
- * @return 0 on success, in case of error:
- *  EINVAL  malformatted SRTCP packet
- *  EACCES  authentication failed (spoofed packet or out-of-sync)
- */
-int
-srtcp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp)
-{
-    size_t len = *lenp;
-
-    if (len < (4u + s->tag_len))
-        return EINVAL;
-    len -= s->tag_len;
-
-    const uint8_t *tag = rtcp_digest (s->rtcp.mac, buf, len);
-    if (memcmp (buf + len, tag, s->tag_len))
-        return EACCES;
-
-    len -= 4; /* Remove SRTCP index before decryption */
-    *lenp = len;
-    return srtcp_crypt (s, buf, len);
-}
\ No newline at end of file