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freeswitch/libs/srtp/srtp/srtp.c

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/*
* srtp.c
*
* the secure real-time transport protocol
*
* David A. McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright (c) 2001-2005, Cisco Systems, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* Neither the name of the Cisco Systems, Inc. nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#include "srtp.h"
#include "aes_icm.h" /* aes_icm is used in the KDF */
#include "alloc.h" /* for crypto_alloc() */
#ifndef SRTP_KERNEL
# include <limits.h>
# ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
# elif defined(HAVE_WINSOCK2_H)
# include <winsock2.h>
# endif
#endif /* ! SRTP_KERNEL */
extern cipher_type_t aes_icm;
extern auth_type_t tmmhv2;
/* the debug module for srtp */
debug_module_t mod_srtp = {
0, /* debugging is off by default */
"srtp" /* printable name for module */
};
#define octets_in_rtp_header 12
#define uint32s_in_rtp_header 3
#define octets_in_rtcp_header 8
#define uint32s_in_rtcp_header 2
err_status_t
srtp_stream_alloc(srtp_stream_ctx_t **str_ptr,
const srtp_policy_t *p) {
srtp_stream_ctx_t *str;
err_status_t stat;
/*
* This function allocates the stream context, rtp and rtcp ciphers
* and auth functions, and key limit structure. If there is a
* failure during allocation, we free all previously allocated
* memory and return a failure code. The code could probably
* be improved, but it works and should be clear.
*/
/* allocate srtp stream and set str_ptr */
str = (srtp_stream_ctx_t *) crypto_alloc(sizeof(srtp_stream_ctx_t));
if (str == NULL)
return err_status_alloc_fail;
*str_ptr = str;
/* allocate cipher */
stat = crypto_kernel_alloc_cipher(p->rtp.cipher_type,
&str->rtp_cipher,
p->rtp.cipher_key_len);
if (stat) {
crypto_free(str);
return stat;
}
/* allocate auth function */
stat = crypto_kernel_alloc_auth(p->rtp.auth_type,
&str->rtp_auth,
p->rtp.auth_key_len,
p->rtp.auth_tag_len);
if (stat) {
cipher_dealloc(str->rtp_cipher);
crypto_free(str);
return stat;
}
/* allocate key limit structure */
str->limit = crypto_alloc(sizeof(key_limit_ctx_t));
if (str->limit == NULL) {
auth_dealloc(str->rtp_auth);
cipher_dealloc(str->rtp_cipher);
crypto_free(str);
return err_status_alloc_fail;
}
/*
* ...and now the RTCP-specific initialization - first, allocate
* the cipher
*/
stat = crypto_kernel_alloc_cipher(p->rtcp.cipher_type,
&str->rtcp_cipher,
p->rtcp.cipher_key_len);
if (stat) {
auth_dealloc(str->rtp_auth);
cipher_dealloc(str->rtp_cipher);
crypto_free(str->limit);
crypto_free(str);
return stat;
}
/* allocate auth function */
stat = crypto_kernel_alloc_auth(p->rtcp.auth_type,
&str->rtcp_auth,
p->rtcp.auth_key_len,
p->rtcp.auth_tag_len);
if (stat) {
cipher_dealloc(str->rtcp_cipher);
auth_dealloc(str->rtp_auth);
cipher_dealloc(str->rtp_cipher);
crypto_free(str->limit);
crypto_free(str);
return stat;
}
return err_status_ok;
}
err_status_t
srtp_stream_dealloc(srtp_t session, srtp_stream_ctx_t *stream) {
err_status_t status;
/*
* we use a conservative deallocation strategy - if any deallocation
* fails, then we report that fact without trying to deallocate
* anything else
*/
/* deallocate cipher, if it is not the same as that in template */
if (session->stream_template
&& stream->rtp_cipher == session->stream_template->rtp_cipher) {
/* do nothing */
} else {
status = cipher_dealloc(stream->rtp_cipher);
if (status)
return status;
}
/* deallocate auth function, if it is not the same as that in template */
if (session->stream_template
&& stream->rtp_auth == session->stream_template->rtp_auth) {
/* do nothing */
} else {
status = auth_dealloc(stream->rtp_auth);
if (status)
return status;
}
/* deallocate key usage limit, if it is not the same as that in template */
if (session->stream_template
&& stream->limit == session->stream_template->limit) {
/* do nothing */
} else {
crypto_free(stream->limit);
}
/*
* deallocate rtcp cipher, if it is not the same as that in
* template
*/
if (session->stream_template
&& stream->rtcp_cipher == session->stream_template->rtcp_cipher) {
/* do nothing */
} else {
status = cipher_dealloc(stream->rtcp_cipher);
if (status)
return status;
}
/*
* deallocate rtcp auth function, if it is not the same as that in
* template
*/
if (session->stream_template
&& stream->rtcp_auth == session->stream_template->rtcp_auth) {
/* do nothing */
} else {
status = auth_dealloc(stream->rtcp_auth);
if (status)
return status;
}
/* deallocate srtp stream context */
crypto_free(stream);
return err_status_ok;
}
/*
* srtp_stream_clone(stream_template, new) allocates a new stream and
* initializes it using the cipher and auth of the stream_template
*
* the only unique data in a cloned stream is the replay database and
* the SSRC
*/
err_status_t
srtp_stream_clone(const srtp_stream_ctx_t *stream_template,
uint32_t ssrc,
srtp_stream_ctx_t **str_ptr) {
err_status_t status;
srtp_stream_ctx_t *str;
debug_print(mod_srtp, "cloning stream (SSRC: 0x%08x)", ssrc);
/* allocate srtp stream and set str_ptr */
str = (srtp_stream_ctx_t *) crypto_alloc(sizeof(srtp_stream_ctx_t));
if (str == NULL)
return err_status_alloc_fail;
*str_ptr = str;
/* set cipher and auth pointers to those of the template */
str->rtp_cipher = stream_template->rtp_cipher;
str->rtp_auth = stream_template->rtp_auth;
str->rtcp_cipher = stream_template->rtcp_cipher;
str->rtcp_auth = stream_template->rtcp_auth;
/* set key limit to point to that of the template */
status = key_limit_clone(stream_template->limit, &str->limit);
if (status)
return status;
/* initialize replay databases */
rdbx_init(&str->rtp_rdbx);
rdb_init(&str->rtcp_rdb);
/* set ssrc to that provided */
str->ssrc = ssrc;
/* set direction and security services */
str->direction = stream_template->direction;
str->rtp_services = stream_template->rtp_services;
str->rtcp_services = stream_template->rtcp_services;
/* defensive coding */
str->next = NULL;
return err_status_ok;
}
/*
* key derivation functions, internal to libSRTP
*
* srtp_kdf_t is a key derivation context
*
* srtp_kdf_init(&kdf, k) initializes kdf with the key k
*
* srtp_kdf_generate(&kdf, l, kl, keylen) derives the key
* corresponding to label l and puts it into kl; the length
* of the key in octets is provided as keylen. this function
* should be called once for each subkey that is derived.
*
* srtp_kdf_clear(&kdf) zeroizes the kdf state
*/
typedef enum {
label_rtp_encryption = 0x00,
label_rtp_msg_auth = 0x01,
label_rtp_salt = 0x02,
label_rtcp_encryption = 0x03,
label_rtcp_msg_auth = 0x04,
label_rtcp_salt = 0x05
} srtp_prf_label;
/*
* srtp_kdf_t represents a key derivation function. The SRTP
* default KDF is the only one implemented at present.
*/
typedef struct {
aes_icm_ctx_t c; /* cipher used for key derivation */
} srtp_kdf_t;
err_status_t
srtp_kdf_init(srtp_kdf_t *kdf, const uint8_t key[30]) {
aes_icm_context_init(&kdf->c, key);
return err_status_ok;
}
err_status_t
srtp_kdf_generate(srtp_kdf_t *kdf, srtp_prf_label label,
uint8_t *key, int length) {
v128_t nonce;
/* set eigth octet of nonce to <label>, set the rest of it to zero */
v128_set_to_zero(&nonce);
nonce.v8[7] = label;
aes_icm_set_iv(&kdf->c, &nonce);
/* generate keystream output */
aes_icm_output(&kdf->c, key, length);
return err_status_ok;
}
err_status_t
srtp_kdf_clear(srtp_kdf_t *kdf) {
/* zeroize aes context */
octet_string_set_to_zero((uint8_t *)kdf, sizeof(srtp_kdf_t));
return err_status_ok;
}
/*
* end of key derivation functions
*/
#define MAX_SRTP_KEY_LEN 256
err_status_t
srtp_stream_init(srtp_stream_ctx_t *srtp,
const srtp_policy_t *p) {
err_status_t stat;
srtp_kdf_t kdf;
uint8_t tmp_key[MAX_SRTP_KEY_LEN];
uint8_t *key = p->key;
debug_print(mod_srtp, "initializing stream (SSRC: 0x%08x)",
p->ssrc.value);
/* initialize replay database */
rdbx_init(&srtp->rtp_rdbx);
/* initialize key limit to maximum value */
#ifdef NO_64BIT_MATH
{
uint64_t temp;
temp = make64(UINT_MAX,UINT_MAX);
key_limit_set(srtp->limit, temp);
}
#else
key_limit_set(srtp->limit, 0xffffffffffffLL);
#endif
/* set the SSRC value */
srtp->ssrc = htonl(p->ssrc.value);
/* set the security service flags */
srtp->rtp_services = p->rtp.sec_serv;
srtp->rtcp_services = p->rtcp.sec_serv;
/*
* set direction to unknown - this flag gets checked in srtp_protect(),
* srtp_unprotect(), srtp_protect_rtcp(), and srtp_unprotect_rtcp(), and
* gets set appropriately if it is set to unknown.
*/
srtp->direction = dir_unknown;
/* initialize KDF state */
srtp_kdf_init(&kdf, key);
/* generate encryption key */
srtp_kdf_generate(&kdf, label_rtp_encryption,
tmp_key, cipher_get_key_length(srtp->rtp_cipher));
/*
* if the cipher in the srtp context is aes_icm, then we need
* to generate the salt value
*/
if (srtp->rtp_cipher->type == &aes_icm) {
/* FIX!!! this is really the cipher key length; rest is salt */
int base_key_len = 16;
int salt_len = cipher_get_key_length(srtp->rtp_cipher) - base_key_len;
debug_print(mod_srtp, "found aes_icm, generating salt", NULL);
/* generate encryption salt, put after encryption key */
srtp_kdf_generate(&kdf, label_rtp_salt,
tmp_key + base_key_len, salt_len);
}
debug_print(mod_srtp, "cipher key: %s",
octet_string_hex_string(tmp_key,
cipher_get_key_length(srtp->rtp_cipher)));
/* initialize cipher */
stat = cipher_init(srtp->rtp_cipher, tmp_key, direction_any);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return err_status_init_fail;
}
/* generate authentication key */
srtp_kdf_generate(&kdf, label_rtp_msg_auth,
tmp_key, auth_get_key_length(srtp->rtp_auth));
debug_print(mod_srtp, "auth key: %s",
octet_string_hex_string(tmp_key,
auth_get_key_length(srtp->rtp_auth)));
/* initialize auth function */
stat = auth_init(srtp->rtp_auth, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return err_status_init_fail;
}
/*
* ...now initialize RTCP-specific structures
*/
/* initialize replay database */
rdb_init(&srtp->rtcp_rdb);
/* DAM - no RTCP key limit at present */
/* generate encryption key */
srtp_kdf_generate(&kdf, label_rtcp_encryption,
tmp_key, cipher_get_key_length(srtp->rtcp_cipher));
/*
* if the cipher in the srtp context is aes_icm, then we need
* to generate the salt value
*/
if (srtp->rtcp_cipher->type == &aes_icm) {
/* FIX!!! this is really the cipher key length; rest is salt */
int base_key_len = 16;
int salt_len = cipher_get_key_length(srtp->rtcp_cipher) - base_key_len;
debug_print(mod_srtp, "found aes_icm, generating rtcp salt", NULL);
/* generate encryption salt, put after encryption key */
srtp_kdf_generate(&kdf, label_rtcp_salt,
tmp_key + base_key_len, salt_len);
}
debug_print(mod_srtp, "rtcp cipher key: %s",
octet_string_hex_string(tmp_key,
cipher_get_key_length(srtp->rtcp_cipher)));
/* initialize cipher */
stat = cipher_init(srtp->rtcp_cipher, tmp_key, direction_any);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return err_status_init_fail;
}
/* generate authentication key */
srtp_kdf_generate(&kdf, label_rtcp_msg_auth,
tmp_key, auth_get_key_length(srtp->rtcp_auth));
debug_print(mod_srtp, "rtcp auth key: %s",
octet_string_hex_string(tmp_key,
auth_get_key_length(srtp->rtcp_auth)));
/* initialize auth function */
stat = auth_init(srtp->rtcp_auth, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return err_status_init_fail;
}
/* clear memory then return */
srtp_kdf_clear(&kdf);
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return err_status_ok;
}
/*
* srtp_event_reporter is an event handler function that merely
* reports the events that are reported by the callbacks
*/
void
srtp_event_reporter(srtp_event_data_t *data) {
err_report(err_level_warning, "srtp: in stream 0x%x: ",
data->stream->ssrc);
switch(data->event) {
case event_ssrc_collision:
err_report(err_level_warning, "\tSSRC collision\n");
break;
case event_key_soft_limit:
err_report(err_level_warning, "\tkey usage soft limit reached\n");
break;
case event_key_hard_limit:
err_report(err_level_warning, "\tkey usage hard limit reached\n");
break;
case event_packet_index_limit:
err_report(err_level_warning, "\tpacket index limit reached\n");
break;
default:
err_report(err_level_warning, "\tunknown event reported to handler\n");
}
}
/*
* srtp_event_handler is a global variable holding a pointer to the
* event handler function; this function is called for any unexpected
* event that needs to be handled out of the SRTP data path. see
* srtp_event_t in srtp.h for more info
*
* it is okay to set srtp_event_handler to NULL, but we set
* it to the srtp_event_reporter.
*/
static srtp_event_handler_func_t *srtp_event_handler = srtp_event_reporter;
err_status_t
srtp_install_event_handler(srtp_event_handler_func_t func) {
/*
* note that we accept NULL arguments intentionally - calling this
* function with a NULL arguments removes an event handler that's
* been previously installed
*/
/* set global event handling function */
srtp_event_handler = func;
return err_status_ok;
}
err_status_t
srtp_protect(srtp_ctx_t *ctx, void *rtp_hdr, int *pkt_octet_len) {
srtp_hdr_t *hdr = rtp_hdr;
uint32_t *enc_start; /* pointer to start of encrypted portion */
uint32_t *auth_start; /* pointer to start of auth. portion */
unsigned enc_octet_len = 0; /* number of octets in encrypted portion */
xtd_seq_num_t est; /* estimated xtd_seq_num_t of *hdr */
int delta; /* delta of local pkt idx and that in hdr */
uint8_t *auth_tag = NULL; /* location of auth_tag within packet */
err_status_t status;
int tag_len;
srtp_stream_ctx_t *stream;
int prefix_len;
debug_print(mod_srtp, "function srtp_protect", NULL);
/* we assume the hdr is 32-bit aligned to start */
/* check the packet length - it must at least contain a full header */
if (*pkt_octet_len < octets_in_rtp_header)
return err_status_bad_param;
/*
* look up ssrc in srtp_stream list, and process the packet with
* the appropriate stream. if we haven't seen this stream before,
* there's a template key for this srtp_session, and the cipher
* supports key-sharing, then we assume that a new stream using
* that key has just started up
*/
stream = srtp_get_stream(ctx, hdr->ssrc);
if (stream == NULL) {
if (ctx->stream_template != NULL) {
srtp_stream_ctx_t *new_stream;
/* allocate and initialize a new stream */
status = srtp_stream_clone(ctx->stream_template,
hdr->ssrc, &new_stream);
if (status)
return status;
/* add new stream to the head of the stream_list */
new_stream->next = ctx->stream_list;
ctx->stream_list = new_stream;
/* set direction to outbound */
new_stream->direction = dir_srtp_sender;
/* set stream (the pointer used in this function) */
stream = new_stream;
} else {
/* no template stream, so we return an error */
return err_status_no_ctx;
}
}
/*
* verify that stream is for sending traffic - this check will
* detect SSRC collisions, since a stream that appears in both
* srtp_protect() and srtp_unprotect() will fail this test in one of
* those functions.
*/
if (stream->direction != dir_srtp_sender) {
if (stream->direction == dir_unknown) {
stream->direction = dir_srtp_sender;
} else {
srtp_handle_event(ctx, stream, event_ssrc_collision);
}
}
/*
* update the key usage limit, and check it to make sure that we
* didn't just hit either the soft limit or the hard limit, and call
* the event handler if we hit either.
*/
switch(key_limit_update(stream->limit)) {
case key_event_normal:
break;
case key_event_soft_limit:
srtp_handle_event(ctx, stream, event_key_soft_limit);
break;
case key_event_hard_limit:
srtp_handle_event(ctx, stream, event_key_hard_limit);
return err_status_key_expired;
default:
break;
}
/* get tag length from stream */
tag_len = auth_get_tag_length(stream->rtp_auth);
/*
* find starting point for encryption and length of data to be
* encrypted - the encrypted portion starts after the rtp header
* extension, if present; otherwise, it starts after the last csrc,
* if any are present
*
* if we're not providing confidentiality, set enc_start to NULL
*/
if (stream->rtp_services & sec_serv_conf) {
enc_start = (uint32_t *)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
srtp_hdr_xtnd_t *xtn_hdr = (srtp_hdr_xtnd_t *)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
enc_octet_len = (unsigned int)(*pkt_octet_len - ((enc_start - (uint32_t *)hdr) << 2));
} else {
enc_start = NULL;
}
/*
* if we're providing authentication, set the auth_start and auth_tag
* pointers to the proper locations; otherwise, set auth_start to NULL
* to indicate that no authentication is needed
*/
if (stream->rtp_services & sec_serv_auth) {
auth_start = (uint32_t *)hdr;
auth_tag = (uint8_t *)hdr + *pkt_octet_len;
} else {
auth_start = NULL;
auth_tag = NULL;
}
/*
* estimate the packet index using the start of the replay window
* and the sequence number from the header
*/
delta = rdbx_estimate_index(&stream->rtp_rdbx, &est, ntohs(hdr->seq));
status = rdbx_check(&stream->rtp_rdbx, delta);
if (status)
return status; /* we've been asked to reuse an index */
rdbx_add_index(&stream->rtp_rdbx, delta);
#ifdef NO_64BIT_MATH
debug_print2(mod_srtp, "estimated packet index: %08x%08x",
high32(est),low32(est));
#else
debug_print(mod_srtp, "estimated packet index: %016llx", est);
#endif
/*
* if we're using rindael counter mode, set nonce and seq
*/
if (stream->rtp_cipher->type == &aes_icm) {
v128_t iv;
iv.v32[0] = 0;
iv.v32[1] = hdr->ssrc;
#ifdef NO_64BIT_MATH
iv.v64[1] = be64_to_cpu(make64((high32(est) << 16) | (low32(est) >> 16),
low32(est) << 16));
#else
iv.v64[1] = be64_to_cpu(est << 16);
#endif
status = cipher_set_iv(stream->rtp_cipher, &iv);
} else {
v128_t iv;
/* otherwise, set the index to est */
#ifdef NO_64BIT_MATH
iv.v32[0] = 0;
iv.v32[1] = 0;
#else
iv.v64[0] = 0;
#endif
iv.v64[1] = be64_to_cpu(est);
status = cipher_set_iv(stream->rtp_cipher, &iv);
}
if (status)
return err_status_cipher_fail;
/* shift est, put into network byte order */
#ifdef NO_64BIT_MATH
est = be64_to_cpu(make64((high32(est) << 16) |
(low32(est) >> 16),
low32(est) << 16));
#else
est = be64_to_cpu(est << 16);
#endif
/*
* if we're authenticating using a universal hash, put the keystream
* prefix into the authentication tag
*/
if (auth_start) {
prefix_len = auth_get_prefix_length(stream->rtp_auth);
if (prefix_len) {
status = cipher_output(stream->rtp_cipher, auth_tag, prefix_len);
if (status)
return err_status_cipher_fail;
debug_print(mod_srtp, "keystream prefix: %s",
octet_string_hex_string(auth_tag, prefix_len));
}
}
/* if we're encrypting, exor keystream into the message */
if (enc_start) {
status = cipher_encrypt(stream->rtp_cipher,
(uint8_t *)enc_start, &enc_octet_len);
if (status)
return err_status_cipher_fail;
}
/*
* if we're authenticating, run authentication function and put result
* into the auth_tag
*/
if (auth_start) {
/* initialize auth func context */
status = auth_start(stream->rtp_auth);
if (status) return status;
/* run auth func over packet */
status = auth_update(stream->rtp_auth,
(uint8_t *)auth_start, *pkt_octet_len);
if (status) return status;
/* run auth func over ROC, put result into auth_tag */
debug_print(mod_srtp, "estimated packet index: %016llx", est);
status = auth_compute(stream->rtp_auth, (uint8_t *)&est, 4, auth_tag);
debug_print(mod_srtp, "srtp auth tag: %s",
octet_string_hex_string(auth_tag, tag_len));
if (status)
return err_status_auth_fail;
}
if (auth_tag) {
/* increase the packet length by the length of the auth tag */
*pkt_octet_len += tag_len;
}
return err_status_ok;
}
err_status_t
srtp_unprotect(srtp_ctx_t *ctx, void *srtp_hdr, int *pkt_octet_len) {
srtp_hdr_t *hdr = srtp_hdr;
uint32_t *enc_start; /* pointer to start of encrypted portion */
uint32_t *auth_start; /* pointer to start of auth. portion */
uint32_t enc_octet_len = 0;/* number of octets in encrypted portion */
uint8_t *auth_tag = NULL; /* location of auth_tag within packet */
xtd_seq_num_t est; /* estimated xtd_seq_num_t of *hdr */
int delta; /* delta of local pkt idx and that in hdr */
v128_t iv;
err_status_t status;
srtp_stream_ctx_t *stream;
uint8_t tmp_tag[SRTP_MAX_TAG_LEN];
int tag_len, prefix_len;
debug_print(mod_srtp, "function srtp_unprotect", NULL);
/* we assume the hdr is 32-bit aligned to start */
/* check the packet length - it must at least contain a full header */
if (*pkt_octet_len < octets_in_rtp_header)
return err_status_bad_param;
/*
* look up ssrc in srtp_stream list, and process the packet with
* the appropriate stream. if we haven't seen this stream before,
* there's only one key for this srtp_session, and the cipher
* supports key-sharing, then we assume that a new stream using
* that key has just started up
*/
stream = srtp_get_stream(ctx, hdr->ssrc);
if (stream == NULL) {
if (ctx->stream_template != NULL) {
stream = ctx->stream_template;
debug_print(mod_srtp, "using provisional stream (SSRC: 0x%08x)",
hdr->ssrc);
/*
* set estimated packet index to sequence number from header,
* and set delta equal to the same value
*/
#ifdef NO_64BIT_MATH
est = (xtd_seq_num_t) make64(0,ntohs(hdr->seq));
delta = low32(est);
#else
est = (xtd_seq_num_t) ntohs(hdr->seq);
delta = (int)est;
#endif
} else {
/*
* no stream corresponding to SSRC found, and we don't do
* key-sharing, so return an error
*/
return err_status_no_ctx;
}
} else {
/* estimate packet index from seq. num. in header */
delta = rdbx_estimate_index(&stream->rtp_rdbx, &est, ntohs(hdr->seq));
/* check replay database */
status = rdbx_check(&stream->rtp_rdbx, delta);
if (status)
return status;
}
#ifdef NO_64BIT_MATH
debug_print2(mod_srtp, "estimated u_packet index: %08x%08x", high32(est),low32(est));
#else
debug_print(mod_srtp, "estimated u_packet index: %016llx", est);
#endif
/* get tag length from stream */
tag_len = auth_get_tag_length(stream->rtp_auth);
/*
* set the cipher's IV properly, depending on whatever cipher we
* happen to be using
*/
if (stream->rtp_cipher->type == &aes_icm) {
/* aes counter mode */
iv.v32[0] = 0;
iv.v32[1] = hdr->ssrc; /* still in network order */
#ifdef NO_64BIT_MATH
iv.v64[1] = be64_to_cpu(make64((high32(est) << 16) | (low32(est) >> 16),
low32(est) << 16));
#else
iv.v64[1] = be64_to_cpu(est << 16);
#endif
status = aes_icm_set_iv(stream->rtp_cipher->state, &iv);
} else {
/* no particular format - set the iv to the pakcet index */
#ifdef NO_64BIT_MATH
iv.v32[0] = 0;
iv.v32[1] = 0;
#else
iv.v64[0] = 0;
#endif
iv.v64[1] = be64_to_cpu(est);
status = cipher_set_iv(stream->rtp_cipher, &iv);
}
if (status)
return err_status_cipher_fail;
/* shift est, put into network byte order */
#ifdef NO_64BIT_MATH
est = be64_to_cpu(make64((high32(est) << 16) |
(low32(est) >> 16),
low32(est) << 16));
#else
est = be64_to_cpu(est << 16);
#endif
/*
* find starting point for decryption and length of data to be
* decrypted - the encrypted portion starts after the rtp header
* extension, if present; otherwise, it starts after the last csrc,
* if any are present
*
* if we're not providing confidentiality, set enc_start to NULL
*/
if (stream->rtp_services & sec_serv_conf) {
enc_start = (uint32_t *)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
srtp_hdr_xtnd_t *xtn_hdr = (srtp_hdr_xtnd_t *)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
enc_octet_len = (uint32_t)(*pkt_octet_len - tag_len - ((enc_start - (uint32_t *)hdr) << 2));
} else {
enc_start = NULL;
}
/*
* if we're providing authentication, set the auth_start and auth_tag
* pointers to the proper locations; otherwise, set auth_start to NULL
* to indicate that no authentication is needed
*/
if (stream->rtp_services & sec_serv_auth) {
auth_start = (uint32_t *)hdr;
auth_tag = (uint8_t *)hdr + *pkt_octet_len - tag_len;
} else {
auth_start = NULL;
auth_tag = NULL;
}
/*
* if we expect message authentication, run the authentication
* function and compare the result with the value of the auth_tag
*/
if (auth_start) {
/*
* if we're using a universal hash, then we need to compute the
* keystream prefix for encrypting the universal hash output
*
* if the keystream prefix length is zero, then we know that
* the authenticator isn't using a universal hash function
*/
if (stream->rtp_auth->prefix_len != 0) {
prefix_len = auth_get_prefix_length(stream->rtp_auth);
status = cipher_output(stream->rtp_cipher, tmp_tag, prefix_len);
debug_print(mod_srtp, "keystream prefix: %s",
octet_string_hex_string(tmp_tag, prefix_len));
if (status)
return err_status_cipher_fail;
}
/* initialize auth func context */
status = auth_start(stream->rtp_auth);
if (status) return status;
/* now compute auth function over packet */
status = auth_update(stream->rtp_auth, (uint8_t *)auth_start,
*pkt_octet_len - tag_len);
/* run auth func over ROC, then write tmp tag */
status = auth_compute(stream->rtp_auth, (uint8_t *)&est, 4, tmp_tag);
debug_print(mod_srtp, "computed auth tag: %s",
octet_string_hex_string(tmp_tag, tag_len));
debug_print(mod_srtp, "packet auth tag: %s",
octet_string_hex_string(auth_tag, tag_len));
if (status)
return err_status_auth_fail;
if (octet_string_is_eq(tmp_tag, auth_tag, tag_len))
return err_status_auth_fail;
}
/*
* update the key usage limit, and check it to make sure that we
* didn't just hit either the soft limit or the hard limit, and call
* the event handler if we hit either.
*/
switch(key_limit_update(stream->limit)) {
case key_event_normal:
break;
case key_event_soft_limit:
srtp_handle_event(ctx, stream, event_key_soft_limit);
break;
case key_event_hard_limit:
srtp_handle_event(ctx, stream, event_key_hard_limit);
return err_status_key_expired;
default:
break;
}
/* if we're encrypting, add keystream into ciphertext */
if (enc_start) {
status = cipher_encrypt(stream->rtp_cipher,
(uint8_t *)enc_start, &enc_octet_len);
if (status)
return err_status_cipher_fail;
}
/*
* verify that stream is for received traffic - this check will
* detect SSRC collisions, since a stream that appears in both
* srtp_protect() and srtp_unprotect() will fail this test in one of
* those functions.
*
* we do this check *after* the authentication check, so that the
* latter check will catch any attempts to fool us into thinking
* that we've got a collision
*/
if (stream->direction != dir_srtp_receiver) {
if (stream->direction == dir_unknown) {
stream->direction = dir_srtp_receiver;
} else {
srtp_handle_event(ctx, stream, event_ssrc_collision);
}
}
/*
* if the stream is a 'provisional' one, in which the template context
* is used, then we need to allocate a new stream at this point, since
* the authentication passed
*/
if (stream == ctx->stream_template) {
srtp_stream_ctx_t *new_stream;
/*
* allocate and initialize a new stream
*
* note that we indicate failure if we can't allocate the new
* stream, and some implementations will want to not return
* failure here
*/
status = srtp_stream_clone(ctx->stream_template, hdr->ssrc, &new_stream);
if (status)
return status;
/* add new stream to the head of the stream_list */
new_stream->next = ctx->stream_list;
ctx->stream_list = new_stream;
/* set stream (the pointer used in this function) */
stream = new_stream;
}
/*
* the message authentication function passed, so add the packet
* index into the replay database
*/
rdbx_add_index(&stream->rtp_rdbx, delta);
/* decrease the packet length by the length of the auth tag */
*pkt_octet_len -= tag_len;
return err_status_ok;
}
err_status_t
srtp_init() {
err_status_t status;
/* initialize crypto kernel */
status = crypto_kernel_init();
if (status)
return status;
/* load srtp debug module into the kernel */
status = crypto_kernel_load_debug_module(&mod_srtp);
if (status)
return status;
return err_status_ok;
}
/*
* The following code is under consideration for removal. See
* SRTP_MAX_TRAILER_LEN
*/
#if 0
/*
* srtp_get_trailer_length(&a) returns the number of octets that will
* be added to an RTP packet by the SRTP processing. This value
* is constant for a given srtp_stream_t (i.e. between initializations).
*/
int
srtp_get_trailer_length(const srtp_stream_t s) {
return auth_get_tag_length(s->rtp_auth);
}
#endif
/*
* srtp_get_stream(ssrc) returns a pointer to the stream corresponding
* to ssrc, or NULL if no stream exists for that ssrc
*
* this is an internal function
*/
srtp_stream_ctx_t *
srtp_get_stream(srtp_t srtp, uint32_t ssrc) {
srtp_stream_ctx_t *stream;
/* walk down list until ssrc is found */
stream = srtp->stream_list;
while (stream != NULL) {
if (stream->ssrc == ssrc)
return stream;
stream = stream->next;
}
/* we haven't found our ssrc, so return a null */
return NULL;
}
err_status_t
srtp_dealloc(srtp_t session) {
srtp_stream_ctx_t *stream;
err_status_t status;
/*
* we take a conservative deallocation strategy - if we encounter an
* error deallocating a stream, then we stop trying to deallocate
* memory and just return an error
*/
/* walk list of streams, deallocating as we go */
stream = session->stream_list;
while (stream != NULL) {
srtp_stream_t next = stream->next;
status = srtp_stream_dealloc(session, stream);
if (status)
return status;
stream = next;
}
/* deallocate stream template, if there is one */
if (session->stream_template != NULL) {
status = auth_dealloc(session->stream_template->rtcp_auth);
if (status)
return status;
status = cipher_dealloc(session->stream_template->rtcp_cipher);
if (status)
return status;
crypto_free(session->stream_template->limit);
status = cipher_dealloc(session->stream_template->rtp_cipher);
if (status)
return status;
status = auth_dealloc(session->stream_template->rtp_auth);
if (status)
return status;
crypto_free(session->stream_template);
}
/* deallocate session context */
crypto_free(session);
return err_status_ok;
}
err_status_t
srtp_add_stream(srtp_t session,
const srtp_policy_t *policy) {
err_status_t status;
srtp_stream_t tmp;
/* sanity check arguments */
if ((session == NULL) || (policy == NULL) || (policy->key == NULL))
return err_status_bad_param;
/* allocate stream */
status = srtp_stream_alloc(&tmp, policy);
if (status) {
return status;
}
/* initialize stream */
status = srtp_stream_init(tmp, policy);
if (status) {
crypto_free(tmp);
return status;
}
/*
* set the head of the stream list or the template to point to the
* stream that we've just alloced and init'ed, depending on whether
* or not it has a wildcard SSRC value or not
*
* if the template stream has already been set, then the policy is
* inconsistent, so we return a bad_param error code
*/
switch (policy->ssrc.type) {
case (ssrc_any_outbound):
if (session->stream_template) {
return err_status_bad_param;
}
session->stream_template = tmp;
session->stream_template->direction = dir_srtp_sender;
break;
case (ssrc_any_inbound):
if (session->stream_template) {
return err_status_bad_param;
}
session->stream_template = tmp;
session->stream_template->direction = dir_srtp_receiver;
break;
case (ssrc_specific):
tmp->next = session->stream_list;
session->stream_list = tmp;
break;
case (ssrc_undefined):
default:
crypto_free(tmp);
return err_status_bad_param;
}
return err_status_ok;
}
err_status_t
srtp_create(srtp_t *session, /* handle for session */
const srtp_policy_t *policy) { /* SRTP policy (list) */
err_status_t stat;
srtp_ctx_t *ctx;
/* sanity check arguments */
if (session == NULL)
return err_status_bad_param;
/* allocate srtp context and set ctx_ptr */
ctx = (srtp_ctx_t *) crypto_alloc(sizeof(srtp_ctx_t));
if (ctx == NULL)
return err_status_alloc_fail;
*session = ctx;
/*
* loop over elements in the policy list, allocating and
* initializing a stream for each element
*/
ctx->stream_template = NULL;
ctx->stream_list = NULL;
while (policy != NULL) {
stat = srtp_add_stream(ctx, policy);
if (stat) {
/* clean up everything */
srtp_dealloc(*session);
return stat;
}
/* set policy to next item in list */
policy = policy->next;
}
return err_status_ok;
}
err_status_t
srtp_remove_stream(srtp_t session, uint32_t ssrc) {
srtp_stream_ctx_t *stream, *last_stream;
err_status_t status;
/* sanity check arguments */
if (session == NULL)
return err_status_bad_param;
/* find stream in list; complain if not found */
last_stream = stream = session->stream_list;
while ((stream != NULL) && (ssrc != stream->ssrc)) {
last_stream = stream;
stream = stream->next;
}
if (stream == NULL)
return err_status_no_ctx;
/* remove stream from the list */
last_stream->next = stream->next;
/* deallocate the stream */
status = srtp_stream_dealloc(session, stream);
if (status)
return status;
return err_status_ok;
}
/*
* the default policy - provides a convenient way for callers to use
* the default security policy
*
* this policy is that defined in the current SRTP internet draft.
*
*/
/*
* NOTE: cipher_key_len is really key len (128 bits) plus salt len
* (112 bits)
*/
/* There are hard-coded 16's for base_key_len in the key generation code */
void
crypto_policy_set_rtp_default(crypto_policy_t *p) {
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30; /* default 128 bits per RFC 3711 */
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20; /* default 160 bits per RFC 3711 */
p->auth_tag_len = 10; /* default 80 bits per RFC 3711 */
p->sec_serv = sec_serv_conf_and_auth;
}
void
crypto_policy_set_rtcp_default(crypto_policy_t *p) {
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30; /* default 128 bits per RFC 3711 */
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20; /* default 160 bits per RFC 3711 */
p->auth_tag_len = 10; /* default 80 bits per RFC 3711 */
p->sec_serv = sec_serv_conf_and_auth;
}
void
crypto_policy_set_aes_cm_128_hmac_sha1_32(crypto_policy_t *p) {
/*
* corresponds to draft-ietf-mmusic-sdescriptions-12.txt
*
* note that this crypto policy is intended for SRTP, but not SRTCP
*/
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30; /* 128 bit key, 112 bit salt */
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20; /* 160 bit key */
p->auth_tag_len = 4; /* 32 bit tag */
p->sec_serv = sec_serv_conf_and_auth;
}
void
crypto_policy_set_aes_cm_128_null_auth(crypto_policy_t *p) {
/*
* corresponds to draft-ietf-mmusic-sdescriptions-12.txt
*
* note that this crypto policy is intended for SRTP, but not SRTCP
*/
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30; /* 128 bit key, 112 bit salt */
p->auth_type = NULL_AUTH;
p->auth_key_len = 0;
p->auth_tag_len = 0;
p->sec_serv = sec_serv_conf;
}
void
crypto_policy_set_null_cipher_hmac_sha1_80(crypto_policy_t *p) {
/*
* corresponds to draft-ietf-mmusic-sdescriptions-12.txt
*/
p->cipher_type = NULL_CIPHER;
p->cipher_key_len = 0;
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20;
p->auth_tag_len = 10;
p->sec_serv = sec_serv_auth;
}
/*
* secure rtcp functions
*/
err_status_t
srtp_protect_rtcp(srtp_t ctx, void *rtcp_hdr, int *pkt_octet_len) {
srtcp_hdr_t *hdr = rtcp_hdr;
uint32_t *enc_start; /* pointer to start of encrypted portion */
uint32_t *auth_start; /* pointer to start of auth. portion */
uint32_t *trailer; /* pointer to start of trailer */
uint32_t enc_octet_len = 0;/* number of octets in encrypted portion */
uint8_t *auth_tag = NULL; /* location of auth_tag within packet */
err_status_t status;
int tag_len;
srtp_stream_ctx_t *stream;
int prefix_len;
uint32_t seq_num;
/* we assume the hdr is 32-bit aligned to start */
/*
* look up ssrc in srtp_stream list, and process the packet with
* the appropriate stream. if we haven't seen this stream before,
* there's only one key for this srtp_session, and the cipher
* supports key-sharing, then we assume that a new stream using
* that key has just started up
*/
stream = srtp_get_stream(ctx, hdr->ssrc);
if (stream == NULL) {
if (ctx->stream_template != NULL) {
srtp_stream_ctx_t *new_stream;
/* allocate and initialize a new stream */
status = srtp_stream_clone(ctx->stream_template,
hdr->ssrc, &new_stream);
if (status)
return status;
/* add new stream to the head of the stream_list */
new_stream->next = ctx->stream_list;
ctx->stream_list = new_stream;
/* set stream (the pointer used in this function) */
stream = new_stream;
} else {
/* no template stream, so we return an error */
return err_status_no_ctx;
}
}
/*
* verify that stream is for sending traffic - this check will
* detect SSRC collisions, since a stream that appears in both
* srtp_protect() and srtp_unprotect() will fail this test in one of
* those functions.
*/
if (stream->direction != dir_srtp_sender) {
if (stream->direction == dir_unknown) {
stream->direction = dir_srtp_sender;
} else {
srtp_handle_event(ctx, stream, event_ssrc_collision);
}
}
/* get tag length from stream context */
tag_len = auth_get_tag_length(stream->rtcp_auth);
/*
* set encryption start and encryption length - if we're not
* providing confidentiality, set enc_start to NULL
*/
enc_start = (uint32_t *)hdr + uint32s_in_rtcp_header;
enc_octet_len = *pkt_octet_len - octets_in_rtcp_header;
/* all of the packet, except the header, gets encrypted */
/* NOTE: hdr->length is not usable - it refers to only the first
RTCP report in the compound packet! */
/* NOTE: trailer is 32-bit aligned because RTCP 'packets' are always
multiples of 32-bits (RFC 3550 6.1) */
trailer = (uint32_t *) ((char *)enc_start + enc_octet_len);
if (stream->rtcp_services & sec_serv_conf) {
*trailer = htonl(SRTCP_E_BIT); /* set encrypt bit */
} else {
enc_start = NULL;
enc_octet_len = 0;
/* 0 is network-order independant */
*trailer = 0x00000000; /* set encrypt bit */
}
/*
* set the auth_start and auth_tag pointers to the proper locations
* (note that srtpc *always* provides authentication, unlike srtp)
*/
/* Note: This would need to change for optional mikey data */
auth_start = (uint32_t *)hdr;
auth_tag = (uint8_t *)hdr + *pkt_octet_len + sizeof(srtcp_trailer_t);
/*
* check sequence number for overruns, and copy it into the packet
* if its value isn't too big
*/
status = rdb_increment(&stream->rtcp_rdb);
if (status)
return status;
seq_num = rdb_get_value(&stream->rtcp_rdb);
*trailer |= htonl(seq_num);
debug_print(mod_srtp, "srtcp index: %x", seq_num);
/*
* if we're using rindael counter mode, set nonce and seq
*/
if (stream->rtcp_cipher->type == &aes_icm) {
v128_t iv;
iv.v32[0] = 0;
iv.v32[1] = hdr->ssrc; /* still in network order! */
iv.v32[2] = htonl(seq_num >> 16);
iv.v32[3] = htonl(seq_num << 16);
status = aes_icm_set_iv(stream->rtcp_cipher->state, &iv);
} else {
v128_t iv;
/* otherwise, just set the index to seq_num */
iv.v32[0] = 0;
iv.v32[1] = 0;
iv.v32[2] = 0;
iv.v32[3] = htonl(seq_num);
status = cipher_set_iv(stream->rtcp_cipher, &iv);
}
if (status)
return err_status_cipher_fail;
/*
* if we're authenticating using a universal hash, put the keystream
* prefix into the authentication tag
*/
/* if auth_start is non-null, then put keystream into tag */
if (auth_start) {
/* put keystream prefix into auth_tag */
prefix_len = auth_get_prefix_length(stream->rtcp_auth);
status = cipher_output(stream->rtcp_cipher, auth_tag, prefix_len);
debug_print(mod_srtp, "keystream prefix: %s",
octet_string_hex_string(auth_tag, prefix_len));
if (status)
return err_status_cipher_fail;
}
/* if we're encrypting, exor keystream into the message */
if (enc_start) {
status = cipher_encrypt(stream->rtcp_cipher,
(uint8_t *)enc_start, &enc_octet_len);
if (status)
return err_status_cipher_fail;
}
/* initialize auth func context */
auth_start(stream->rtcp_auth);
/* per spec, do auth after encryption */
/* run auth func over packet, put result into auth_tag */
status = auth_compute(stream->rtcp_auth,
(uint8_t *)auth_start, *pkt_octet_len, auth_tag);
debug_print(mod_srtp, "srtcp auth tag: %s",
octet_string_hex_string(auth_tag, tag_len));
if (status)
return err_status_auth_fail;
/* increase the packet length by the length of the auth tag and seq_num*/
*pkt_octet_len += (tag_len + sizeof(srtcp_trailer_t));
return err_status_ok;
}
err_status_t
srtp_unprotect_rtcp(srtp_t ctx, void *srtcp_hdr, int *pkt_octet_len) {
srtcp_hdr_t *hdr = srtcp_hdr;
uint32_t *enc_start; /* pointer to start of encrypted portion */
uint32_t *auth_start; /* pointer to start of auth. portion */
uint32_t *trailer; /* pointer to start of trailer */
uint32_t enc_octet_len = 0;/* number of octets in encrypted portion */
uint8_t *auth_tag = NULL; /* location of auth_tag within packet */
uint8_t tmp_tag[SRTP_MAX_TAG_LEN];
err_status_t status;
int tag_len;
srtp_stream_ctx_t *stream;
int prefix_len;
uint32_t seq_num;
/* we assume the hdr is 32-bit aligned to start */
/*
* look up ssrc in srtp_stream list, and process the packet with
* the appropriate stream. if we haven't seen this stream before,
* there's only one key for this srtp_session, and the cipher
* supports key-sharing, then we assume that a new stream using
* that key has just started up
*/
stream = srtp_get_stream(ctx, hdr->ssrc);
if (stream == NULL) {
if (ctx->stream_template != NULL) {
stream = ctx->stream_template;
debug_print(mod_srtp, "srtcp using provisional stream (SSRC: 0x%08x)",
hdr->ssrc);
} else {
/* no template stream, so we return an error */
return err_status_no_ctx;
}
}
/* get tag length from stream context */
tag_len = auth_get_tag_length(stream->rtcp_auth);
/*
* set encryption start, encryption length, and trailer
*/
enc_octet_len = *pkt_octet_len -
(octets_in_rtcp_header + tag_len + sizeof(srtcp_trailer_t));
/* index & E (encryption) bit follow normal data. hdr->len
is the number of words (32-bit) in the normal packet minus 1 */
/* This should point trailer to the word past the end of the
normal data. */
/* This would need to be modified for optional mikey data */
/*
* NOTE: trailer is 32-bit aligned because RTCP 'packets' are always
* multiples of 32-bits (RFC 3550 6.1)
*/
trailer = (uint32_t *) ((char *) hdr +
*pkt_octet_len -(tag_len + sizeof(srtcp_trailer_t)));
if (*((unsigned char *) trailer) & SRTCP_E_BYTE_BIT) {
enc_start = (uint32_t *)hdr + uint32s_in_rtcp_header;
} else {
enc_octet_len = 0;
enc_start = NULL; /* this indicates that there's no encryption */
}
/*
* set the auth_start and auth_tag pointers to the proper locations
* (note that srtcp *always* uses authentication, unlike srtp)
*/
auth_start = (uint32_t *)hdr;
auth_tag = (uint8_t *)hdr + *pkt_octet_len - tag_len;
/*
* check the sequence number for replays
*/
/* this is easier than dealing with bitfield access */
seq_num = ntohl(*trailer) & SRTCP_INDEX_MASK;
status = rdb_check(&stream->rtcp_rdb, seq_num);
if (status)
return status;
debug_print(mod_srtp, "srtcp index: %x", seq_num);
/*
* if we're using aes counter mode, set nonce and seq
*/
if (stream->rtcp_cipher->type == &aes_icm) {
v128_t iv;
iv.v32[0] = 0;
iv.v32[1] = hdr->ssrc; /* still in network order! */
iv.v32[2] = htonl(seq_num >> 16);
iv.v32[3] = htonl(seq_num << 16);
status = aes_icm_set_iv(stream->rtcp_cipher->state, &iv);
} else {
v128_t iv;
/* otherwise, just set the index to seq_num */
iv.v32[0] = 0;
iv.v32[1] = 0;
iv.v32[2] = 0;
iv.v32[3] = htonl(seq_num);
status = cipher_set_iv(stream->rtcp_cipher, &iv);
}
if (status)
return err_status_cipher_fail;
/* initialize auth func context */
auth_start(stream->rtcp_auth);
/* run auth func over packet, put result into tmp_tag */
status = auth_compute(stream->rtcp_auth, (uint8_t *)auth_start,
*pkt_octet_len - (tag_len + sizeof(srtcp_trailer_t)),
tmp_tag);
debug_print(mod_srtp, "srtcp computed tag: %s",
octet_string_hex_string(tmp_tag, tag_len));
if (status)
return err_status_auth_fail;
/* compare the tag just computed with the one in the packet */
debug_print(mod_srtp, "srtcp tag from packet: %s",
octet_string_hex_string(auth_tag, tag_len));
if (octet_string_is_eq(tmp_tag, auth_tag, tag_len))
return err_status_auth_fail;
/*
* if we're authenticating using a universal hash, put the keystream
* prefix into the authentication tag
*/
prefix_len = auth_get_prefix_length(stream->rtcp_auth);
if (prefix_len) {
status = cipher_output(stream->rtcp_cipher, auth_tag, prefix_len);
debug_print(mod_srtp, "keystream prefix: %s",
octet_string_hex_string(auth_tag, prefix_len));
if (status)
return err_status_cipher_fail;
}
/* if we're decrypting, exor keystream into the message */
if (enc_start) {
status = cipher_encrypt(stream->rtcp_cipher,
(uint8_t *)enc_start, &enc_octet_len);
if (status)
return err_status_cipher_fail;
}
/* decrease the packet length by the length of the auth tag and seq_num*/
*pkt_octet_len -= (tag_len + sizeof(srtcp_trailer_t));
/*
* verify that stream is for received traffic - this check will
* detect SSRC collisions, since a stream that appears in both
* srtp_protect() and srtp_unprotect() will fail this test in one of
* those functions.
*
* we do this check *after* the authentication check, so that the
* latter check will catch any attempts to fool us into thinking
* that we've got a collision
*/
if (stream->direction != dir_srtp_receiver) {
if (stream->direction == dir_unknown) {
stream->direction = dir_srtp_receiver;
} else {
srtp_handle_event(ctx, stream, event_ssrc_collision);
}
}
/*
* if the stream is a 'provisional' one, in which the template context
* is used, then we need to allocate a new stream at this point, since
* the authentication passed
*/
if (stream == ctx->stream_template) {
srtp_stream_ctx_t *new_stream;
/*
* allocate and initialize a new stream
*
* note that we indicate failure if we can't allocate the new
* stream, and some implementations will want to not return
* failure here
*/
status = srtp_stream_clone(ctx->stream_template, hdr->ssrc, &new_stream);
if (status)
return status;
/* add new stream to the head of the stream_list */
new_stream->next = ctx->stream_list;
ctx->stream_list = new_stream;
/* set stream (the pointer used in this function) */
stream = new_stream;
}
/* we've passed the authentication check, so add seq_num to the rdb */
rdb_add_index(&stream->rtcp_rdb, seq_num);
return err_status_ok;
}
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