/*
* srtp.c
*
* the secure real-time transport protocol
*
* David A. McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright (c) 2001-2017, 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.
*
*/
// Leave this as the top level import. Ensures the existence of defines
#include "config.h"
#include "srtp_priv.h"
#include "crypto_types.h"
#include "err.h"
#include "alloc.h" /* for srtp_crypto_alloc() */
#ifdef GCM
#include "aes_gcm.h" /* for AES GCM mode */
#endif
#ifdef OPENSSL_KDF
#include <openssl/kdf.h>
#include "aes_icm_ext.h"
#endif
#include <limits.h>
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#elif defined(HAVE_WINSOCK2_H)
#include <winsock2.h>
#endif
/* the debug module for srtp */
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
#define octets_in_rtp_extn_hdr 4
static srtp_err_status_t srtp_validate_rtp_header(
void *rtp_hdr,
int *pkt_octet_len)
{
srtp_hdr_t *hdr = (srtp_hdr_t *)rtp_hdr;
int rtp_header_len;
if (*pkt_octet_len < octets_in_rtp_header)
return srtp_err_status_bad_param;
/* Check RTP header length */
rtp_header_len = octets_in_rtp_header + 4 * hdr->cc;
if (hdr->x == 1)
rtp_header_len += octets_in_rtp_extn_hdr;
if (*pkt_octet_len < rtp_header_len)
return srtp_err_status_bad_param;
/* Verifing profile length. */
if (hdr->x == 1) {
srtp_hdr_xtnd_t *xtn_hdr =
(srtp_hdr_xtnd_t *)((uint32_t *)hdr + uint32s_in_rtp_header +
hdr->cc);
int profile_len = ntohs(xtn_hdr->length);
rtp_header_len += profile_len * 4;
/* profile length counts the number of 32-bit words */
if (*pkt_octet_len < rtp_header_len)
return srtp_err_status_bad_param;
}
return srtp_err_status_ok;
}
const char *srtp_get_version_string()
{
/*
* Simply return the autotools generated string
*/
return SRTP_VER_STRING;
}
unsigned int srtp_get_version()
{
unsigned int major = 0, minor = 0, micro = 0;
unsigned int rv = 0;
int parse_rv;
/*
* Parse the autotools generated version
*/
parse_rv = sscanf(SRTP_VERSION,
"%u.%u.%u", &major, &minor, µ);
if (parse_rv != 3) {
/*
* We're expected to parse all 3 version levels.
* If not, then this must not be an official release.
* Return all zeros on the version
*/
return (0);
}
/*
* We allow 8 bits for the major and minor, while
* allowing 16 bits for the micro. 16 bits for the micro
* may be beneficial for a continuous delivery model
* in the future.
*/
rv |= (major & 0xFF) << 24;
rv |= (minor & 0xFF) << 16;
rv |= micro & 0xFF;
return rv;
}
srtp_err_status_t srtp_stream_dealloc(srtp_stream_ctx_t *stream,
const srtp_stream_ctx_t *stream_template)
{
srtp_err_status_t status;
unsigned int i = 0;
srtp_session_keys_t *session_keys = NULL;
srtp_session_keys_t *template_session_keys = NULL;
/*
* we use a conservative deallocation strategy - if any deallocation
* fails, then we report that fact without trying to deallocate
* anything else
*/
if (stream->session_keys) {
for (i = 0; i < stream->num_master_keys; i++) {
session_keys = &stream->session_keys[i];
if (stream_template &&
stream->num_master_keys == stream_template->num_master_keys) {
template_session_keys = &stream_template->session_keys[i];
}
else {
template_session_keys = NULL;
}
/*
* deallocate cipher, if it is not the same as that in template
*/
if (template_session_keys &&
session_keys->rtp_cipher == template_session_keys->rtp_cipher) {
/* do nothing */
}
else if (session_keys->rtp_cipher) {
status = srtp_cipher_dealloc(session_keys->rtp_cipher);
if (status)
return status;
}
/*
* deallocate auth function, if it is not the same as that in
* template
*/
if (template_session_keys &&
session_keys->rtp_auth == template_session_keys->rtp_auth) {
/* do nothing */
}
else if (session_keys->rtp_auth) {
status = srtp_auth_dealloc(session_keys->rtp_auth);
if (status)
return status;
}
if (template_session_keys &&
session_keys->rtp_xtn_hdr_cipher ==
template_session_keys->rtp_xtn_hdr_cipher) {
/* do nothing */
}
else if (session_keys->rtp_xtn_hdr_cipher) {
status = srtp_cipher_dealloc(session_keys->rtp_xtn_hdr_cipher);
if (status)
return status;
}
/*
* deallocate rtcp cipher, if it is not the same as that in
* template
*/
if (template_session_keys &&
session_keys->rtcp_cipher ==
template_session_keys->rtcp_cipher) {
/* do nothing */
}
else if (session_keys->rtcp_cipher) {
status = srtp_cipher_dealloc(session_keys->rtcp_cipher);
if (status)
return status;
}
/*
* deallocate rtcp auth function, if it is not the same as that in
* template
*/
if (template_session_keys &&
session_keys->rtcp_auth == template_session_keys->rtcp_auth) {
/* do nothing */
}
else if (session_keys->rtcp_auth) {
status = srtp_auth_dealloc(session_keys->rtcp_auth);
if (status)
return status;
}
/*
* zeroize the salt value
*/
octet_string_set_to_zero(session_keys->salt, SRTP_AEAD_SALT_LEN);
octet_string_set_to_zero(session_keys->c_salt, SRTP_AEAD_SALT_LEN);
if (session_keys->mki_id) {
octet_string_set_to_zero(session_keys->mki_id,
session_keys->mki_size);
srtp_crypto_free(session_keys->mki_id);
session_keys->mki_id = NULL;
}
/*
* deallocate key usage limit, if it is not the same as that in
* template
*/
if (template_session_keys &&
session_keys->limit == template_session_keys->limit) {
/* do nothing */
}
else if (session_keys->limit) {
srtp_crypto_free(session_keys->limit);
}
}
srtp_crypto_free(stream->session_keys);
}
status = srtp_rdbx_dealloc(&stream->rtp_rdbx);
if (status)
return status;
if (stream_template &&
stream->enc_xtn_hdr == stream_template->enc_xtn_hdr) {
/* do nothing */
}
else if (stream->enc_xtn_hdr) {
srtp_crypto_free(stream->enc_xtn_hdr);
}
/* deallocate srtp stream context */
srtp_crypto_free(stream);
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_valid_policy(
const srtp_policy_t *p)
{
if (p != NULL && p->deprecated_ekt != NULL) {
return srtp_err_status_bad_param;
}
return srtp_err_status_ok;
}
srtp_err_status_t srtp_stream_alloc(srtp_stream_ctx_t **str_ptr,
const srtp_policy_t *p)
{
srtp_stream_ctx_t *str;
srtp_err_status_t stat;
unsigned int i = 0;
srtp_session_keys_t *session_keys = NULL;
stat = srtp_valid_policy(p);
if (stat != srtp_err_status_ok) {
return 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 *)srtp_crypto_alloc(
sizeof(srtp_stream_ctx_t));
if (str == NULL)
return srtp_err_status_alloc_fail;
*str_ptr = str;
/*
*To keep backwards API compatible if someone is using multiple master
* keys then key should be set to NULL
*/
if (p->key != NULL) {
str->num_master_keys = 1;
}
else {
str->num_master_keys = p->num_master_keys;
}
str->session_keys = (srtp_session_keys_t *)srtp_crypto_alloc(
sizeof(srtp_session_keys_t) * str->num_master_keys);
if (str->session_keys == NULL) {
srtp_stream_dealloc(str, NULL);
return srtp_err_status_alloc_fail;
}
for (i = 0; i < str->num_master_keys; i++) {
session_keys = &str->session_keys[i];
/* allocate cipher */
stat = srtp_crypto_kernel_alloc_cipher(
p->rtp.cipher_type, &session_keys->rtp_cipher,
p->rtp.cipher_key_len, p->rtp.auth_tag_len);
if (stat) {
srtp_stream_dealloc(str, NULL);
return stat;
}
/* allocate auth function */
stat = srtp_crypto_kernel_alloc_auth(
p->rtp.auth_type, &session_keys->rtp_auth, p->rtp.auth_key_len,
p->rtp.auth_tag_len);
if (stat) {
srtp_stream_dealloc(str, NULL);
return stat;
}
/*
* ...and now the RTCP-specific initialization - first, allocate
* the cipher
*/
stat = srtp_crypto_kernel_alloc_cipher(
p->rtcp.cipher_type, &session_keys->rtcp_cipher,
p->rtcp.cipher_key_len, p->rtcp.auth_tag_len);
if (stat) {
srtp_stream_dealloc(str, NULL);
return stat;
}
/* allocate auth function */
stat = srtp_crypto_kernel_alloc_auth(
p->rtcp.auth_type, &session_keys->rtcp_auth, p->rtcp.auth_key_len,
p->rtcp.auth_tag_len);
if (stat) {
srtp_stream_dealloc(str, NULL);
return stat;
}
session_keys->mki_id = NULL;
/* allocate key limit structure */
session_keys->limit = (srtp_key_limit_ctx_t *)srtp_crypto_alloc(
sizeof(srtp_key_limit_ctx_t));
if (session_keys->limit == NULL) {
srtp_stream_dealloc(str, NULL);
return srtp_err_status_alloc_fail;
}
}
if (p->enc_xtn_hdr && p->enc_xtn_hdr_count > 0) {
srtp_cipher_type_id_t enc_xtn_hdr_cipher_type;
int enc_xtn_hdr_cipher_key_len;
str->enc_xtn_hdr = (
int *)srtp_crypto_alloc(p->enc_xtn_hdr_count *
sizeof(p->enc_xtn_hdr[0]));
if (!str->enc_xtn_hdr) {
srtp_stream_dealloc(str, NULL);
return srtp_err_status_alloc_fail;
}
memcpy(str->enc_xtn_hdr, p->enc_xtn_hdr,
p->enc_xtn_hdr_count *
sizeof(p->enc_xtn_hdr[0]));
str->enc_xtn_hdr_count = p->enc_xtn_hdr_count;
/*
* For GCM ciphers, the corresponding ICM cipher is used for header
* extensions encryption.
*/
switch (p->rtp.cipher_type) {
case SRTP_AES_GCM_128:
enc_xtn_hdr_cipher_type = SRTP_AES_ICM_128;
enc_xtn_hdr_cipher_key_len = SRTP_AES_ICM_128_KEY_LEN_WSALT;
break;
case SRTP_AES_GCM_256:
enc_xtn_hdr_cipher_type = SRTP_AES_ICM_256;
enc_xtn_hdr_cipher_key_len = SRTP_AES_ICM_256_KEY_LEN_WSALT;
break;
default:
enc_xtn_hdr_cipher_type = p->rtp.cipher_type;
enc_xtn_hdr_cipher_key_len = p->rtp.cipher_key_len;
break;
}
for (i = 0; i < str->num_master_keys; i++) {
session_keys = &str->session_keys[i];
/* allocate cipher for extensions header encryption */
stat = srtp_crypto_kernel_alloc_cipher(
enc_xtn_hdr_cipher_type, &session_keys->rtp_xtn_hdr_cipher,
enc_xtn_hdr_cipher_key_len, 0);
if (stat) {
srtp_stream_dealloc(str, NULL);
return stat;
}
}
}
else {
for (i = 0; i < str->num_master_keys; i++) {
session_keys = &str->session_keys[i];
session_keys->rtp_xtn_hdr_cipher = NULL;
}
str->enc_xtn_hdr = NULL;
str->enc_xtn_hdr_count = 0;
}
return srtp_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
*/
srtp_err_status_t srtp_stream_clone(
const srtp_stream_ctx_t *stream_template,
uint32_t ssrc,
srtp_stream_ctx_t **str_ptr)
{
srtp_err_status_t status;
srtp_stream_ctx_t *str;
unsigned int i = 0;
srtp_session_keys_t *session_keys = NULL;
const srtp_session_keys_t *template_session_keys = NULL;
debug_print(mod_srtp,
"cloning stream (SSRC: 0x%08x)", ntohl(ssrc));
/* allocate srtp stream and set str_ptr */
str = (srtp_stream_ctx_t *)srtp_crypto_alloc(
sizeof(srtp_stream_ctx_t));
if (str == NULL)
return srtp_err_status_alloc_fail;
*str_ptr = str;
str->num_master_keys = stream_template->num_master_keys;
str->session_keys = (srtp_session_keys_t *)srtp_crypto_alloc(
sizeof(srtp_session_keys_t) * str->num_master_keys);
if (str->session_keys == NULL) {
srtp_stream_dealloc(*str_ptr, stream_template);
*str_ptr = NULL;
return srtp_err_status_alloc_fail;
}
for (i = 0; i < stream_template->num_master_keys; i++) {
session_keys = &str->session_keys[i];
template_session_keys = &stream_template->session_keys[i];
/* set cipher and auth pointers to those of the template */
session_keys->rtp_cipher = template_session_keys->rtp_cipher;
session_keys->rtp_auth = template_session_keys->rtp_auth;
session_keys->rtp_xtn_hdr_cipher =
template_session_keys->rtp_xtn_hdr_cipher;
session_keys->rtcp_cipher = template_session_keys->rtcp_cipher;
session_keys->rtcp_auth = template_session_keys->rtcp_auth;
session_keys->mki_size = template_session_keys->mki_size;
if (template_session_keys->mki_size == 0) {
session_keys->mki_id = NULL;
}
else {
session_keys->mki_id =
srtp_crypto_alloc(template_session_keys->mki_size);
if (session_keys->mki_id == NULL) {
srtp_stream_dealloc(*str_ptr, stream_template);
*str_ptr = NULL;
return srtp_err_status_init_fail;
}
memcpy(session_keys->mki_id, template_session_keys->mki_id,
session_keys->mki_size);
}
/* Copy the salt values */
memcpy(session_keys->salt, template_session_keys->salt,
SRTP_AEAD_SALT_LEN);
memcpy(session_keys->c_salt, template_session_keys->c_salt,
SRTP_AEAD_SALT_LEN);
/* set key limit to point to that of the template */
status = srtp_key_limit_clone(template_session_keys->limit,
&session_keys->limit);
if (status) {
srtp_stream_dealloc(*str_ptr, stream_template);
*str_ptr = NULL;
return status;
}
}
/* initialize replay databases */
status = srtp_rdbx_init(
&str->rtp_rdbx, srtp_rdbx_get_window_size(&stream_template->rtp_rdbx));
if (status) {
srtp_stream_dealloc(*str_ptr, stream_template);
*str_ptr = NULL;
return status;
}
srtp_rdb_init(&str->rtcp_rdb);
str->allow_repeat_tx = stream_template->allow_repeat_tx;
/* set ssrc to that provided */
str->ssrc = ssrc;
/* reset pending ROC */
str->pending_roc = 0;
/* set direction and security services */
str->direction = stream_template->direction;
str->rtp_services = stream_template->rtp_services;
str->rtcp_services = stream_template->rtcp_services;
/* copy information about extensions header encryption */
str->enc_xtn_hdr = stream_template->enc_xtn_hdr;
str->enc_xtn_hdr_count = stream_template->enc_xtn_hdr_count;
/* defensive coding */
str->next = NULL;
return srtp_err_status_ok;
}
/*
* key derivation functions, internal to libSRTP
*
* srtp_kdf_t is a key derivation context
*
* srtp_kdf_init(&kdf, cipher_id, k, keylen) initializes kdf to use cipher
* described by cipher_id, with the master key k with length in octets keylen.
*
* 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 and deallocates 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,
label_rtp_header_encryption = 0x06,
label_rtp_header_salt = 0x07
} srtp_prf_label;
#define MAX_SRTP_KEY_LEN 256
#if defined(OPENSSL) &&
defined(OPENSSL_KDF)
#define MAX_SRTP_AESKEY_LEN 32
#define MAX_SRTP_SALT_LEN 14
/*
* srtp_kdf_t represents a key derivation function. The SRTP
* default KDF is the only one implemented at present.
*/
typedef struct {
uint8_t master_key[MAX_SRTP_AESKEY_LEN];
uint8_t master_salt[MAX_SRTP_SALT_LEN];
const EVP_CIPHER *evp;
} srtp_kdf_t;
static srtp_err_status_t srtp_kdf_init(srtp_kdf_t *kdf,
const uint8_t *key,
int key_len,
int salt_len)
{
memset(kdf, 0x0,
sizeof(srtp_kdf_t));
/* The NULL cipher has zero key length */
if (key_len == 0)
return srtp_err_status_ok;
if ((key_len > MAX_SRTP_AESKEY_LEN) || (salt_len > MAX_SRTP_SALT_LEN)) {
return srtp_err_status_bad_param;
}
switch (key_len) {
case SRTP_AES_256_KEYSIZE:
kdf->evp = EVP_aes_256_ctr();
break;
case SRTP_AES_192_KEYSIZE:
kdf->evp = EVP_aes_192_ctr();
break;
case SRTP_AES_128_KEYSIZE:
kdf->evp = EVP_aes_128_ctr();
break;
default:
return srtp_err_status_bad_param;
break;
}
memcpy(kdf->master_key, key, key_len);
memcpy(kdf->master_salt, key + key_len, salt_len);
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_kdf_generate(srtp_kdf_t *kdf,
srtp_prf_label label,
uint8_t *key,
unsigned int length)
{
int ret;
/* The NULL cipher will not have an EVP */
if (!kdf->evp)
return srtp_err_status_ok;
octet_string_set_to_zero(key, length);
/*
* Invoke the OpenSSL SRTP KDF function
* This is useful if OpenSSL is in FIPS mode and FIP
* compliance is required for SRTP.
*/
ret = kdf_srtp(kdf->evp, (
char *)&kdf->master_key,
(
char *)&kdf->master_salt, NULL, NULL, label, (
char *)key);
if (ret == -1) {
return (srtp_err_status_algo_fail);
}
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_kdf_clear(srtp_kdf_t *kdf)
{
octet_string_set_to_zero(kdf->master_key, MAX_SRTP_AESKEY_LEN);
octet_string_set_to_zero(kdf->master_salt, MAX_SRTP_SALT_LEN);
kdf->evp = NULL;
return srtp_err_status_ok;
}
#else /* if OPENSSL_KDF */
/*
* srtp_kdf_t represents a key derivation function. The SRTP
* default KDF is the only one implemented at present.
*/
typedef struct {
srtp_cipher_t *cipher;
/* cipher used for key derivation */
} srtp_kdf_t;
static srtp_err_status_t srtp_kdf_init(srtp_kdf_t *kdf,
const uint8_t *key,
int key_len)
{
srtp_cipher_type_id_t cipher_id;
srtp_err_status_t stat;
switch (key_len) {
case SRTP_AES_ICM_256_KEY_LEN_WSALT:
cipher_id = SRTP_AES_ICM_256;
break;
case SRTP_AES_ICM_192_KEY_LEN_WSALT:
cipher_id = SRTP_AES_ICM_192;
break;
case SRTP_AES_ICM_128_KEY_LEN_WSALT:
cipher_id = SRTP_AES_ICM_128;
break;
default:
return srtp_err_status_bad_param;
break;
}
stat = srtp_crypto_kernel_alloc_cipher(cipher_id, &kdf->cipher, key_len, 0);
if (stat)
return stat;
stat = srtp_cipher_init(kdf->cipher, key);
if (stat) {
srtp_cipher_dealloc(kdf->cipher);
return stat;
}
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_kdf_generate(srtp_kdf_t *kdf,
srtp_prf_label label,
uint8_t *key,
unsigned int length)
{
srtp_err_status_t status;
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;
status = srtp_cipher_set_iv(kdf->cipher, (uint8_t *)&nonce,
srtp_direction_encrypt);
if (status)
return status;
/* generate keystream output */
octet_string_set_to_zero(key, length);
status = srtp_cipher_encrypt(kdf->cipher, key, &length);
if (status)
return status;
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_kdf_clear(srtp_kdf_t *kdf)
{
srtp_err_status_t status;
status = srtp_cipher_dealloc(kdf->cipher);
if (status)
return status;
kdf->cipher = NULL;
return srtp_err_status_ok;
}
#endif /* else OPENSSL_KDF */
/*
* end of key derivation functions
*/
/* Get the base key length corresponding to a given combined key+salt
* length for the given cipher.
* TODO: key and salt lengths should be separate fields in the policy. */
static inline int base_key_length(
const srtp_cipher_type_t *cipher,
int key_length)
{
switch (cipher->id) {
case SRTP_NULL_CIPHER:
return 0;
case SRTP_AES_ICM_128:
case SRTP_AES_ICM_192:
case SRTP_AES_ICM_256:
/* The legacy modes are derived from
* the configured key length on the policy */
return key_length - SRTP_SALT_LEN;
case SRTP_AES_GCM_128:
return key_length - SRTP_AEAD_SALT_LEN;
case SRTP_AES_GCM_256:
return key_length - SRTP_AEAD_SALT_LEN;
default:
return key_length;
}
}
/* Get the key length that the application should supply for the given cipher */
static inline int full_key_length(
const srtp_cipher_type_t *cipher)
{
switch (cipher->id) {
case SRTP_NULL_CIPHER:
case SRTP_AES_ICM_128:
return SRTP_AES_ICM_128_KEY_LEN_WSALT;
case SRTP_AES_ICM_192:
return SRTP_AES_ICM_192_KEY_LEN_WSALT;
case SRTP_AES_ICM_256:
return SRTP_AES_ICM_256_KEY_LEN_WSALT;
case SRTP_AES_GCM_128:
return SRTP_AES_GCM_128_KEY_LEN_WSALT;
case SRTP_AES_GCM_256:
return SRTP_AES_GCM_256_KEY_LEN_WSALT;
default:
return 0;
}
}
unsigned int srtp_validate_policy_master_keys(
const srtp_policy_t *policy)
{
unsigned long i = 0;
if (policy->key == NULL) {
if (policy->num_master_keys <= 0)
return 0;
if (policy->num_master_keys > SRTP_MAX_NUM_MASTER_KEYS)
return 0;
for (i = 0; i < policy->num_master_keys; i++) {
if (policy->keys[i]->key == NULL)
return 0;
if (policy->keys[i]->mki_size > SRTP_MAX_MKI_LEN)
return 0;
}
}
return 1;
}
srtp_session_keys_t *srtp_get_session_keys_with_mki_index(
srtp_stream_ctx_t *stream,
unsigned int use_mki,
unsigned int mki_index)
{
if (use_mki) {
if (mki_index >= stream->num_master_keys) {
return NULL;
}
return &stream->session_keys[mki_index];
}
return &stream->session_keys[0];
}
unsigned int srtp_inject_mki(uint8_t *mki_tag_location,
srtp_session_keys_t *session_keys,
unsigned int use_mki)
{
unsigned int mki_size = 0;
if (use_mki) {
mki_size = session_keys->mki_size;
if (mki_size != 0) {
// Write MKI into memory
memcpy(mki_tag_location, session_keys->mki_id, mki_size);
}
}
return mki_size;
}
srtp_err_status_t srtp_stream_init_all_master_keys(
srtp_stream_ctx_t *srtp,
unsigned char *key,
srtp_master_key_t **keys,
const unsigned int max_master_keys)
{
unsigned int i = 0;
srtp_err_status_t status = srtp_err_status_ok;
srtp_master_key_t single_master_key;
if (key != NULL) {
srtp->num_master_keys = 1;
single_master_key.key = key;
single_master_key.mki_id = NULL;
single_master_key.mki_size = 0;
status = srtp_stream_init_keys(srtp, &single_master_key, 0);
}
else {
srtp->num_master_keys = max_master_keys;
for (i = 0; i < srtp->num_master_keys && i < SRTP_MAX_NUM_MASTER_KEYS;
i++) {
status = srtp_stream_init_keys(srtp, keys[i], i);
if (status) {
return status;
}
}
}
return status;
}
srtp_err_status_t srtp_stream_init_keys(srtp_stream_ctx_t *srtp,
srtp_master_key_t *master_key,
const unsigned int current_mki_index)
{
srtp_err_status_t stat;
srtp_kdf_t kdf;
uint8_t tmp_key[MAX_SRTP_KEY_LEN];
int input_keylen, input_keylen_rtcp;
int kdf_keylen = 30, rtp_keylen, rtcp_keylen;
int rtp_base_key_len, rtp_salt_len;
int rtcp_base_key_len, rtcp_salt_len;
srtp_session_keys_t *session_keys = NULL;
unsigned char *key = master_key->key;
/* If RTP or RTCP have a key length > AES-128, assume matching kdf. */
/* TODO: kdf algorithm, master key length, and master salt length should
* be part of srtp_policy_t.
*/
session_keys = &srtp->session_keys[current_mki_index];
/* initialize key limit to maximum value */
#ifdef NO_64BIT_MATH
{
uint64_t temp;
temp = make64(UINT_MAX, UINT_MAX);
srtp_key_limit_set(session_keys->limit, temp);
}
#else
srtp_key_limit_set(session_keys->limit, 0xffffffffffffLL);
#endif
if (master_key->mki_size != 0) {
session_keys->mki_id = srtp_crypto_alloc(master_key->mki_size);
if (session_keys->mki_id == NULL) {
return srtp_err_status_init_fail;
}
memcpy(session_keys->mki_id, master_key->mki_id, master_key->mki_size);
}
else {
session_keys->mki_id = NULL;
}
session_keys->mki_size = master_key->mki_size;
input_keylen = full_key_length(session_keys->rtp_cipher->type);
input_keylen_rtcp = full_key_length(session_keys->rtcp_cipher->type);
if (input_keylen_rtcp > input_keylen) {
input_keylen = input_keylen_rtcp;
}
rtp_keylen = srtp_cipher_get_key_length(session_keys->rtp_cipher);
rtcp_keylen = srtp_cipher_get_key_length(session_keys->rtcp_cipher);
rtp_base_key_len =
base_key_length(session_keys->rtp_cipher->type, rtp_keylen);
rtp_salt_len = rtp_keylen - rtp_base_key_len;
if (rtp_keylen > kdf_keylen) {
kdf_keylen = 46;
/* AES-CTR mode is always used for KDF */
}
if (rtcp_keylen > kdf_keylen) {
kdf_keylen = 46;
/* AES-CTR mode is always used for KDF */
}
if (input_keylen > kdf_keylen) {
kdf_keylen = 46;
/* AES-CTR mode is always used for KDF */
}
debug_print(mod_srtp,
"input key len: %d", input_keylen);
debug_print(mod_srtp,
"srtp key len: %d", rtp_keylen);
debug_print(mod_srtp,
"srtcp key len: %d", rtcp_keylen);
debug_print(mod_srtp,
"base key len: %d", rtp_base_key_len);
debug_print(mod_srtp,
"kdf key len: %d", kdf_keylen);
debug_print(mod_srtp,
"rtp salt len: %d", rtp_salt_len);
/*
* Make sure the key given to us is 'zero' appended. GCM
* mode uses a shorter master SALT (96 bits), but still relies on
* the legacy CTR mode KDF, which uses a 112 bit master SALT.
*/
memset(tmp_key, 0x0, MAX_SRTP_KEY_LEN);
memcpy(tmp_key, key, input_keylen);
/* initialize KDF state */
#if defined(OPENSSL) &&
defined(OPENSSL_KDF)
stat = srtp_kdf_init(&kdf, (
const uint8_t *)tmp_key, rtp_base_key_len,
rtp_salt_len);
#else
stat = srtp_kdf_init(&kdf, (
const uint8_t *)tmp_key, kdf_keylen);
#endif
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
/* generate encryption key */
stat = srtp_kdf_generate(&kdf, label_rtp_encryption, tmp_key,
rtp_base_key_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
debug_print(mod_srtp,
"cipher key: %s",
srtp_octet_string_hex_string(tmp_key, rtp_base_key_len));
/*
* if the cipher in the srtp context uses a salt, then we need
* to generate the salt value
*/
if (rtp_salt_len > 0) {
debug_print0(mod_srtp,
"found rtp_salt_len > 0, generating salt");
/* generate encryption salt, put after encryption key */
stat = srtp_kdf_generate(&kdf, label_rtp_salt,
tmp_key + rtp_base_key_len, rtp_salt_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
memcpy(session_keys->salt, tmp_key + rtp_base_key_len,
SRTP_AEAD_SALT_LEN);
}
if (rtp_salt_len > 0) {
debug_print(mod_srtp,
"cipher salt: %s",
srtp_octet_string_hex_string(tmp_key + rtp_base_key_len,
rtp_salt_len));
}
/* initialize cipher */
stat = srtp_cipher_init(session_keys->rtp_cipher, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
if (session_keys->rtp_xtn_hdr_cipher) {
/* generate extensions header encryption key */
int rtp_xtn_hdr_keylen;
int rtp_xtn_hdr_base_key_len;
int rtp_xtn_hdr_salt_len;
srtp_kdf_t tmp_kdf;
srtp_kdf_t *xtn_hdr_kdf;
if (session_keys->rtp_xtn_hdr_cipher->type !=
session_keys->rtp_cipher->type) {
/*
* With GCM ciphers, the header extensions are still encrypted using
* the corresponding ICM cipher.
* See https://tools.ietf.org/html/rfc7714#section-8.3
*/
uint8_t tmp_xtn_hdr_key[MAX_SRTP_KEY_LEN];
rtp_xtn_hdr_keylen =
srtp_cipher_get_key_length(session_keys->rtp_xtn_hdr_cipher);
rtp_xtn_hdr_base_key_len = base_key_length(
session_keys->rtp_xtn_hdr_cipher->type, rtp_xtn_hdr_keylen);
rtp_xtn_hdr_salt_len =
rtp_xtn_hdr_keylen - rtp_xtn_hdr_base_key_len;
if (rtp_xtn_hdr_salt_len > rtp_salt_len) {
switch (session_keys->rtp_cipher->type->id) {
case SRTP_AES_GCM_128:
case SRTP_AES_GCM_256:
/*
* The shorter GCM salt is padded to the required ICM salt
* length.
*/
rtp_xtn_hdr_salt_len = rtp_salt_len;
break;
default:
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_bad_param;
}
}
memset(tmp_xtn_hdr_key, 0x0, MAX_SRTP_KEY_LEN);
memcpy(tmp_xtn_hdr_key, key,
(rtp_xtn_hdr_base_key_len + rtp_xtn_hdr_salt_len));
xtn_hdr_kdf = &tmp_kdf;
/* initialize KDF state */
#if defined(OPENSSL) &&
defined(OPENSSL_KDF)
stat =
srtp_kdf_init(xtn_hdr_kdf, (
const uint8_t *)tmp_xtn_hdr_key,
rtp_xtn_hdr_base_key_len, rtp_xtn_hdr_salt_len);
#else
stat = srtp_kdf_init(xtn_hdr_kdf, (
const uint8_t *)tmp_xtn_hdr_key,
kdf_keylen);
#endif
octet_string_set_to_zero(tmp_xtn_hdr_key, MAX_SRTP_KEY_LEN);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
}
else {
/* Reuse main KDF. */
rtp_xtn_hdr_keylen = rtp_keylen;
rtp_xtn_hdr_base_key_len = rtp_base_key_len;
rtp_xtn_hdr_salt_len = rtp_salt_len;
xtn_hdr_kdf = &kdf;
}
stat = srtp_kdf_generate(xtn_hdr_kdf, label_rtp_header_encryption,
tmp_key, rtp_xtn_hdr_base_key_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
debug_print(
mod_srtp,
"extensions cipher key: %s",
srtp_octet_string_hex_string(tmp_key, rtp_xtn_hdr_base_key_len));
/*
* if the cipher in the srtp context uses a salt, then we need
* to generate the salt value
*/
if (rtp_xtn_hdr_salt_len > 0) {
debug_print0(mod_srtp,
"found rtp_xtn_hdr_salt_len > 0, generating salt");
/* generate encryption salt, put after encryption key */
stat = srtp_kdf_generate(xtn_hdr_kdf, label_rtp_header_salt,
tmp_key + rtp_xtn_hdr_base_key_len,
rtp_xtn_hdr_salt_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
}
if (rtp_xtn_hdr_salt_len > 0) {
debug_print(
mod_srtp,
"extensions cipher salt: %s",
srtp_octet_string_hex_string(tmp_key + rtp_xtn_hdr_base_key_len,
rtp_xtn_hdr_salt_len));
}
/* initialize extensions header cipher */
stat = srtp_cipher_init(session_keys->rtp_xtn_hdr_cipher, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
if (xtn_hdr_kdf != &kdf) {
/* release memory for custom header extension encryption kdf */
stat = srtp_kdf_clear(xtn_hdr_kdf);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
}
}
/* generate authentication key */
stat = srtp_kdf_generate(&kdf, label_rtp_msg_auth, tmp_key,
srtp_auth_get_key_length(session_keys->rtp_auth));
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
debug_print(mod_srtp,
"auth key: %s",
srtp_octet_string_hex_string(
tmp_key, srtp_auth_get_key_length(session_keys->rtp_auth)));
/* initialize auth function */
stat = srtp_auth_init(session_keys->rtp_auth, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
/*
* ...now initialize SRTCP keys
*/
rtcp_base_key_len =
base_key_length(session_keys->rtcp_cipher->type, rtcp_keylen);
rtcp_salt_len = rtcp_keylen - rtcp_base_key_len;
debug_print(mod_srtp,
"rtcp salt len: %d", rtcp_salt_len);
/* generate encryption key */
stat = srtp_kdf_generate(&kdf, label_rtcp_encryption, tmp_key,
rtcp_base_key_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
/*
* if the cipher in the srtp context uses a salt, then we need
* to generate the salt value
*/
if (rtcp_salt_len > 0) {
debug_print0(mod_srtp,
"found rtcp_salt_len > 0, generating rtcp salt");
/* generate encryption salt, put after encryption key */
stat = srtp_kdf_generate(&kdf, label_rtcp_salt,
tmp_key + rtcp_base_key_len, rtcp_salt_len);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
memcpy(session_keys->c_salt, tmp_key + rtcp_base_key_len,
SRTP_AEAD_SALT_LEN);
}
debug_print(mod_srtp,
"rtcp cipher key: %s",
srtp_octet_string_hex_string(tmp_key, rtcp_base_key_len));
if (rtcp_salt_len > 0) {
debug_print(mod_srtp,
"rtcp cipher salt: %s",
srtp_octet_string_hex_string(tmp_key + rtcp_base_key_len,
rtcp_salt_len));
}
/* initialize cipher */
stat = srtp_cipher_init(session_keys->rtcp_cipher, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
/* generate authentication key */
stat = srtp_kdf_generate(&kdf, label_rtcp_msg_auth, tmp_key,
srtp_auth_get_key_length(session_keys->rtcp_auth));
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
debug_print(
mod_srtp,
"rtcp auth key: %s",
srtp_octet_string_hex_string(
tmp_key, srtp_auth_get_key_length(session_keys->rtcp_auth)));
/* initialize auth function */
stat = srtp_auth_init(session_keys->rtcp_auth, tmp_key);
if (stat) {
/* zeroize temp buffer */
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
return srtp_err_status_init_fail;
}
/* clear memory then return */
stat = srtp_kdf_clear(&kdf);
octet_string_set_to_zero(tmp_key, MAX_SRTP_KEY_LEN);
if (stat)
return srtp_err_status_init_fail;
return srtp_err_status_ok;
}
srtp_err_status_t srtp_stream_init(srtp_stream_ctx_t *srtp,
const srtp_policy_t *p)
{
srtp_err_status_t err;
err = srtp_valid_policy(p);
if (err != srtp_err_status_ok) {
return err;
}
debug_print(mod_srtp,
"initializing stream (SSRC: 0x%08x)", p->ssrc.value);
/* initialize replay database */
/*
* window size MUST be at least 64. MAY be larger. Values more than
* 2^15 aren't meaningful due to how extended sequence numbers are
* calculated.
* Let a window size of 0 imply the default value.
*/
if (p->window_size != 0 &&
(p->window_size < 64 || p->window_size >= 0x8000))
return srtp_err_status_bad_param;
if (p->window_size != 0)
err = srtp_rdbx_init(&srtp->rtp_rdbx, p->window_size);
else
err = srtp_rdbx_init(&srtp->rtp_rdbx, 128);
if (err)
return err;
/* set the SSRC value */
srtp->ssrc = htonl(p->ssrc.value);
/* reset pending ROC */
srtp->pending_roc = 0;
/* 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 SRTCP replay database */
srtp_rdb_init(&srtp->rtcp_rdb);
/* initialize allow_repeat_tx */
/* guard against uninitialized memory: allow only 0 or 1 here */
if (p->allow_repeat_tx != 0 && p->allow_repeat_tx != 1) {
srtp_rdbx_dealloc(&srtp->rtp_rdbx);
return srtp_err_status_bad_param;
}
srtp->allow_repeat_tx = p->allow_repeat_tx;
/* DAM - no RTCP key limit at present */
/* initialize keys */
err = srtp_stream_init_all_master_keys(srtp, p->key, p->keys,
p->num_master_keys);
if (err) {
srtp_rdbx_dealloc(&srtp->rtp_rdbx);
return err;
}
return srtp_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)
{
srtp_err_report(srtp_err_level_warning,
"srtp: in stream 0x%x: ",
data->ssrc);
switch (data->event) {
case event_ssrc_collision:
srtp_err_report(srtp_err_level_warning,
"\tSSRC collision\n");
break;
case event_key_soft_limit:
srtp_err_report(srtp_err_level_warning,
"\tkey usage soft limit reached\n");
break;
case event_key_hard_limit:
srtp_err_report(srtp_err_level_warning,
"\tkey usage hard limit reached\n");
break;
case event_packet_index_limit:
srtp_err_report(srtp_err_level_warning,
"\tpacket index limit reached\n");
break;
default:
srtp_err_report(srtp_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;
srtp_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 srtp_err_status_ok;
}
/*
* Check if the given extension header id is / should be encrypted.
* Returns 1 if yes, otherwise 0.
*/
static int srtp_protect_extension_header(srtp_stream_ctx_t *stream,
int id)
{
int *enc_xtn_hdr = stream->enc_xtn_hdr;
int count = stream->enc_xtn_hdr_count;
if (!enc_xtn_hdr || count <= 0) {
return 0;
}
while (count > 0) {
if (*enc_xtn_hdr == id) {
return 1;
}
enc_xtn_hdr++;
count--;
}
return 0;
}
/*
* extensions header encryption RFC 6904
*/
static srtp_err_status_t srtp_process_header_encryption(
srtp_stream_ctx_t *stream,
srtp_hdr_xtnd_t *xtn_hdr,
srtp_session_keys_t *session_keys)
{
srtp_err_status_t status;
uint8_t keystream[257];
/* Maximum 2 bytes header + 255 bytes data. */
int keystream_pos;
uint8_t *xtn_hdr_data = ((uint8_t *)xtn_hdr) + octets_in_rtp_extn_hdr;
uint8_t *xtn_hdr_end =
xtn_hdr_data + (ntohs(xtn_hdr->length) *
sizeof(uint32_t));
if (ntohs(xtn_hdr->profile_specific) == 0xbede) {
/* RFC 5285, section 4.2. One-Byte Header */
while (xtn_hdr_data < xtn_hdr_end) {
uint8_t xid = (*xtn_hdr_data & 0xf0) >> 4;
unsigned int xlen = (*xtn_hdr_data & 0x0f) + 1;
uint32_t xlen_with_header = 1 + xlen;
xtn_hdr_data++;
if (xtn_hdr_data + xlen > xtn_hdr_end)
return srtp_err_status_parse_err;
if (xid == 15) {
/* found header 15, stop further processing. */
break;
}
status = srtp_cipher_output(session_keys->rtp_xtn_hdr_cipher,
keystream, &xlen_with_header);
if (status)
return srtp_err_status_cipher_fail;
if (srtp_protect_extension_header(stream, xid)) {
keystream_pos = 1;
while (xlen > 0) {
*xtn_hdr_data ^= keystream[keystream_pos++];
xtn_hdr_data++;
xlen--;
}
}
else {
xtn_hdr_data += xlen;
}
/* skip padding bytes. */
while (xtn_hdr_data < xtn_hdr_end && *xtn_hdr_data == 0) {
xtn_hdr_data++;
}
}
}
else if ((ntohs(xtn_hdr->profile_specific) & 0xfff0) == 0x1000) {
/* RFC 5285, section 4.3. Two-Byte Header */
while (xtn_hdr_data + 1 < xtn_hdr_end) {
uint8_t xid = *xtn_hdr_data;
unsigned int xlen = *(xtn_hdr_data + 1);
uint32_t xlen_with_header = 2 + xlen;
xtn_hdr_data += 2;
if (xtn_hdr_data + xlen > xtn_hdr_end)
return srtp_err_status_parse_err;
status = srtp_cipher_output(session_keys->rtp_xtn_hdr_cipher,
keystream, &xlen_with_header);
if (status)
return srtp_err_status_cipher_fail;
if (xlen > 0 && srtp_protect_extension_header(stream, xid)) {
keystream_pos = 2;
while (xlen > 0) {
*xtn_hdr_data ^= keystream[keystream_pos++];
xtn_hdr_data++;
xlen--;
}
}
else {
xtn_hdr_data += xlen;
}
/* skip padding bytes. */
while (xtn_hdr_data < xtn_hdr_end && *xtn_hdr_data == 0) {
xtn_hdr_data++;
}
}
}
else {
/* unsupported extension header format. */
return srtp_err_status_parse_err;
}
return srtp_err_status_ok;
}
/*
* AEAD uses a new IV formation method. This function implements
* section 8.1. (SRTP IV Formation for AES-GCM) of RFC7714.
* The calculation is defined as, where (+) is the xor operation:
*
*
* 0 0 0 0 0 0 0 0 0 0 1 1
* 0 1 2 3 4 5 6 7 8 9 0 1
* +--+--+--+--+--+--+--+--+--+--+--+--+
* |00|00| SSRC | ROC | SEQ |---+
* +--+--+--+--+--+--+--+--+--+--+--+--+ |
* |
* +--+--+--+--+--+--+--+--+--+--+--+--+ |
* | Encryption Salt |->(+)
* +--+--+--+--+--+--+--+--+--+--+--+--+ |
* |
* +--+--+--+--+--+--+--+--+--+--+--+--+ |
* | Initialization Vector |<--+
* +--+--+--+--+--+--+--+--+--+--+--+--+*
*
* Input: *session_keys - pointer to SRTP stream context session keys,
* used to retrieve the SALT
* *iv - Pointer to receive the calculated IV
* *seq - The ROC and SEQ value to use for the
* IV calculation.
* *hdr - The RTP header, used to get the SSRC value
*
*/
static void srtp_calc_aead_iv(srtp_session_keys_t *session_keys,
v128_t *iv,
srtp_xtd_seq_num_t *seq,
srtp_hdr_t *hdr)
{
v128_t in;
v128_t salt;
#ifdef NO_64BIT_MATH
uint32_t local_roc = ((high32(*seq) << 16) | (low32(*seq) >> 16));
uint16_t local_seq = (uint16_t)(low32(*seq));
#else
uint32_t local_roc = (uint32_t)(*seq >> 16);
uint16_t local_seq = (uint16_t)*seq;
#endif
memset(&in, 0,
sizeof(v128_t));
memset(&salt, 0,
sizeof(v128_t));
in.v16[5] = htons(local_seq);
local_roc = htonl(local_roc);
memcpy(&in.v16[3], &local_roc,
sizeof(local_roc));
/*
* Copy in the RTP SSRC value
*/
memcpy(&in.v8[2], &hdr->ssrc, 4);
debug_print(mod_srtp,
"Pre-salted RTP IV = %s\n", v128_hex_string(&in));
/*
* Get the SALT value from the context
*/
memcpy(salt.v8, session_keys->salt, SRTP_AEAD_SALT_LEN);
debug_print(mod_srtp,
"RTP SALT = %s\n", v128_hex_string(&salt));
/*
* Finally, apply tyhe SALT to the input
*/
v128_xor(iv, &in, &salt);
}
srtp_session_keys_t *srtp_get_session_keys(srtp_stream_ctx_t *stream,
uint8_t *hdr,
const unsigned int *pkt_octet_len,
unsigned int *mki_size)
{
unsigned int base_mki_start_location = *pkt_octet_len;
unsigned int mki_start_location = 0;
unsigned int tag_len = 0;
unsigned int i = 0;
// Determine the authentication tag size
if (stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_128 ||
stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_256) {
tag_len = 0;
}
else {
tag_len = srtp_auth_get_tag_length(stream->session_keys[0].rtp_auth);
}
if (tag_len > base_mki_start_location) {
*mki_size = 0;
return NULL;
}
base_mki_start_location -= tag_len;
for (i = 0; i < stream->num_master_keys; i++) {
if (stream->session_keys[i].mki_size != 0 &&
stream->session_keys[i].mki_size <= base_mki_start_location) {
*mki_size = stream->session_keys[i].mki_size;
mki_start_location = base_mki_start_location - *mki_size;
if (memcmp(hdr + mki_start_location, stream->session_keys[i].mki_id,
*mki_size) == 0) {
return &stream->session_keys[i];
}
}
}
*mki_size = 0;
return NULL;
}
static srtp_err_status_t srtp_estimate_index(srtp_rdbx_t *rdbx,
uint32_t roc,
srtp_xtd_seq_num_t *est,
srtp_sequence_number_t seq,
int *delta)
{
#ifdef NO_64BIT_MATH
uint32_t internal_pkt_idx_reduced;
uint32_t external_pkt_idx_reduced;
uint32_t internal_roc;
uint32_t roc_difference;
#endif
#ifdef NO_64BIT_MATH
*est = (srtp_xtd_seq_num_t)make64(roc >> 16, (roc << 16) | seq);
*delta = low32(est) - rdbx->index;
#else
*est = (srtp_xtd_seq_num_t)(((uint64_t)roc) << 16) | seq;
*delta = (
int)(*est - rdbx->index);
#endif
if (*est > rdbx->index) {
#ifdef NO_64BIT_MATH
internal_roc = (uint32_t)(rdbx->index >> 16);
roc_difference = roc - internal_roc;
if (roc_difference > 1) {
*delta = 0;
return srtp_err_status_pkt_idx_adv;
}
internal_pkt_idx_reduced = (uint32_t)(rdbx->index & 0xFFFF);
external_pkt_idx_reduced = (uint32_t)((roc_difference << 16) | seq);
if (external_pkt_idx_reduced - internal_pkt_idx_reduced >
seq_num_median) {
*delta = 0;
return srtp_err_status_pkt_idx_adv;
}
#else
if (*est - rdbx->index > seq_num_median) {
*delta = 0;
return srtp_err_status_pkt_idx_adv;
}
#endif
}
else if (*est < rdbx->index) {
#ifdef NO_64BIT_MATH
internal_roc = (uint32_t)(rdbx->index >> 16);
roc_difference = internal_roc - roc;
if (roc_difference > 1) {
*delta = 0;
return srtp_err_status_pkt_idx_adv;
}
internal_pkt_idx_reduced =
(uint32_t)((roc_difference << 16) | rdbx->index & 0xFFFF);
external_pkt_idx_reduced = (uint32_t)(seq);
if (internal_pkt_idx_reduced - external_pkt_idx_reduced >
seq_num_median) {
*delta = 0;
return srtp_err_status_pkt_idx_old;
}
#else
if (rdbx->index - *est > seq_num_median) {
*delta = 0;
return srtp_err_status_pkt_idx_old;
}
#endif
}
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_get_est_pkt_index(srtp_hdr_t *hdr,
srtp_stream_ctx_t *stream,
srtp_xtd_seq_num_t *est,
int *delta)
{
srtp_err_status_t result = srtp_err_status_ok;
if (stream->pending_roc) {
result = srtp_estimate_index(&stream->rtp_rdbx, stream->pending_roc,
est, ntohs(hdr->seq), delta);
}
else {
/* estimate packet index from seq. num. in header */
*delta =
srtp_rdbx_estimate_index(&stream->rtp_rdbx, est, ntohs(hdr->seq));
}
#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: %016" PRIx64, *est);
#endif
return result;
}
/*
* This function handles outgoing SRTP packets while in AEAD mode,
* which currently supports AES-GCM encryption. All packets are
* encrypted and authenticated.
*/
static srtp_err_status_t srtp_protect_aead(srtp_ctx_t *ctx,
srtp_stream_ctx_t *stream,
void *rtp_hdr,
unsigned int *pkt_octet_len,
srtp_session_keys_t *session_keys,
unsigned int use_mki)
{
srtp_hdr_t *hdr = (srtp_hdr_t *)rtp_hdr;
uint32_t *enc_start;
/* pointer to start of encrypted portion */
int enc_octet_len = 0;
/* number of octets in encrypted portion */
srtp_xtd_seq_num_t est;
/* estimated xtd_seq_num_t of *hdr */
int delta;
/* delta of local pkt idx and that in hdr */
srtp_err_status_t status;
uint32_t tag_len;
v128_t iv;
unsigned int aad_len;
srtp_hdr_xtnd_t *xtn_hdr = NULL;
unsigned int mki_size = 0;
uint8_t *mki_location = NULL;
debug_print0(mod_srtp,
"function srtp_protect_aead");
/*
* 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 (srtp_key_limit_update(session_keys->limit)) {
case srtp_key_event_normal:
break;
case srtp_key_event_hard_limit:
srtp_handle_event(ctx, stream, event_key_hard_limit);
return srtp_err_status_key_expired;
case srtp_key_event_soft_limit:
default:
srtp_handle_event(ctx, stream, event_key_soft_limit);
break;
}
/* get tag length from stream */
tag_len = srtp_auth_get_tag_length(session_keys->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
*/
enc_start = (uint32_t *)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
xtn_hdr = (srtp_hdr_xtnd_t *)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
/* note: the passed size is without the auth tag */
if (!((uint8_t *)enc_start <= (uint8_t *)hdr + *pkt_octet_len))
return srtp_err_status_parse_err;
enc_octet_len =
(
int)(*pkt_octet_len - ((uint8_t *)enc_start - (uint8_t *)hdr));
if (enc_octet_len < 0)
return srtp_err_status_parse_err;
/*
* estimate the packet index using the start of the replay window
* and the sequence number from the header
*/
delta = srtp_rdbx_estimate_index(&stream->rtp_rdbx, &est, ntohs(hdr->seq));
status = srtp_rdbx_check(&stream->rtp_rdbx, delta);
if (status) {
if (status != srtp_err_status_replay_fail || !stream->allow_repeat_tx) {
return status;
/* we've been asked to reuse an index */
}
}
else {
srtp_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: %016" PRIx64, est);
#endif
/*
* AEAD uses a new IV formation method
*/
srtp_calc_aead_iv(session_keys, &iv, &est, hdr);
/* 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
status = srtp_cipher_set_iv(session_keys->rtp_cipher, (uint8_t *)&iv,
srtp_direction_encrypt);
if (!status && session_keys->rtp_xtn_hdr_cipher) {
iv.v32[0] = 0;
iv.v32[1] = hdr->ssrc;
iv.v64[1] = est;
status = srtp_cipher_set_iv(session_keys->rtp_xtn_hdr_cipher,
(uint8_t *)&iv, srtp_direction_encrypt);
}
if (status) {
return srtp_err_status_cipher_fail;
}
if (xtn_hdr && session_keys->rtp_xtn_hdr_cipher) {
/*
* extensions header encryption RFC 6904
*/
status = srtp_process_header_encryption(stream, xtn_hdr, session_keys);
if (status) {
return status;
}
}
/*
* Set the AAD over the RTP header
*/
aad_len = (uint8_t *)enc_start - (uint8_t *)hdr;
status =
srtp_cipher_set_aad(session_keys->rtp_cipher, (uint8_t *)hdr, aad_len);
if (status) {
return (srtp_err_status_cipher_fail);
}
/* Encrypt the payload */
status = srtp_cipher_encrypt(session_keys->rtp_cipher, (uint8_t *)enc_start,
(
unsigned int *)&enc_octet_len);
if (status) {
return srtp_err_status_cipher_fail;
}
/*
* If we're doing GCM, we need to get the tag
* and append that to the output
*/
status =
srtp_cipher_get_tag(session_keys->rtp_cipher,
(uint8_t *)enc_start + enc_octet_len, &tag_len);
if (status) {
return (srtp_err_status_cipher_fail);
}
mki_location = (uint8_t *)hdr + *pkt_octet_len + tag_len;
mki_size = srtp_inject_mki(mki_location, session_keys, use_mki);
/* increase the packet length by the length of the auth tag */
*pkt_octet_len += tag_len;
/* increase the packet length by the length of the mki_size */
*pkt_octet_len += mki_size;
return srtp_err_status_ok;
}
/*
* This function handles incoming SRTP packets while in AEAD mode,
* which currently supports AES-GCM encryption. All packets are
* encrypted and authenticated. Note, the auth tag is at the end
* of the packet stream and is automatically checked by GCM
* when decrypting the payload.
*/
static srtp_err_status_t srtp_unprotect_aead(srtp_ctx_t *ctx,
srtp_stream_ctx_t *stream,
int delta,
srtp_xtd_seq_num_t est,
void *srtp_hdr,
unsigned int *pkt_octet_len,
srtp_session_keys_t *session_keys,
unsigned int mki_size)
{
srtp_hdr_t *hdr = (srtp_hdr_t *)srtp_hdr;
uint32_t *enc_start;
/* pointer to start of encrypted portion */
unsigned int enc_octet_len = 0;
/* number of octets in encrypted portion */
v128_t iv;
srtp_err_status_t status;
int tag_len;
unsigned int aad_len;
srtp_hdr_xtnd_t *xtn_hdr = NULL;
debug_print0(mod_srtp,
"function srtp_unprotect_aead");
#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: %016" PRIx64, est);
#endif
/* get tag length from stream */
tag_len = srtp_auth_get_tag_length(session_keys->rtp_auth);
/*
* AEAD uses a new IV formation method
*/
srtp_calc_aead_iv(session_keys, &iv, &est, hdr);
status = srtp_cipher_set_iv(session_keys->rtp_cipher, (uint8_t *)&iv,
srtp_direction_decrypt);
if (!status && session_keys->rtp_xtn_hdr_cipher) {
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 = srtp_cipher_set_iv(session_keys->rtp_xtn_hdr_cipher,
(uint8_t *)&iv, srtp_direction_encrypt);
}
if (status) {
return srtp_err_status_cipher_fail;
}
/*
* 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
*/
enc_start = (uint32_t *)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
xtn_hdr = (srtp_hdr_xtnd_t *)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
if (!((uint8_t *)enc_start <=
(uint8_t *)hdr + (*pkt_octet_len - tag_len - mki_size)))
return srtp_err_status_parse_err;
/*
* We pass the tag down to the cipher when doing GCM mode
*/
enc_octet_len = (
unsigned int)(*pkt_octet_len - mki_size -
((uint8_t *)enc_start - (uint8_t *)hdr));
/*
* Sanity check the encrypted payload length against
* the tag size. It must always be at least as large
* as the tag length.
*/
if (enc_octet_len < (
unsigned int)tag_len) {
return srtp_err_status_cipher_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 (srtp_key_limit_update(session_keys->limit)) {
case srtp_key_event_normal:
break;
case srtp_key_event_soft_limit:
srtp_handle_event(ctx, stream, event_key_soft_limit);
break;
case srtp_key_event_hard_limit:
--> --------------------
--> maximum size reached
--> --------------------
