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Diffstat (limited to 'plugins/rtp/src/srtp.c')
| -rw-r--r-- | plugins/rtp/src/srtp.c | 836 |
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); -}
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