Mon Aug 31 12:30:12 2015

Asterisk developer's documentation


sdp_crypto.c

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 2006 - 2007, Mikael Magnusson
00005  *
00006  * Mikael Magnusson <mikma@users.sourceforge.net>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 
00019 /*! \file sdp_crypto.c
00020  *
00021  * \brief SDP Security descriptions
00022  *
00023  * Specified in RFC 4568
00024  *
00025  * \author Mikael Magnusson <mikma@users.sourceforge.net>
00026  */
00027 
00028 /*** MODULEINFO
00029    <support_level>core</support_level>
00030  ***/
00031 
00032 #include "asterisk.h"
00033 
00034 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 415908 $")
00035 
00036 #include "asterisk/options.h"
00037 #include "asterisk/utils.h"
00038 #include "include/sdp_crypto.h"
00039 
00040 #define SRTP_MASTER_LEN 30
00041 #define SRTP_MASTERKEY_LEN 16
00042 #define SRTP_MASTERSALT_LEN ((SRTP_MASTER_LEN) - (SRTP_MASTERKEY_LEN))
00043 #define SRTP_MASTER_LEN64 (((SRTP_MASTER_LEN) * 8 + 5) / 6 + 1)
00044 
00045 extern struct ast_srtp_res *res_srtp;
00046 extern struct ast_srtp_policy_res *res_srtp_policy;
00047 
00048 struct sdp_crypto {
00049    char *a_crypto;
00050    unsigned char local_key[SRTP_MASTER_LEN];
00051    char *tag;
00052    char local_key64[SRTP_MASTER_LEN64];
00053    unsigned char remote_key[SRTP_MASTER_LEN];
00054    char suite[64];
00055 };
00056 
00057 static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound);
00058 
00059 static struct sdp_crypto *sdp_crypto_alloc(void)
00060 {
00061    return ast_calloc(1, sizeof(struct sdp_crypto));
00062 }
00063 
00064 void sdp_crypto_destroy(struct sdp_crypto *crypto)
00065 {
00066    ast_free(crypto->a_crypto);
00067    crypto->a_crypto = NULL;
00068    ast_free(crypto->tag);
00069    crypto->tag = NULL;
00070    ast_free(crypto);
00071 }
00072 
00073 struct sdp_crypto *sdp_crypto_setup(void)
00074 {
00075    struct sdp_crypto *p;
00076    int key_len;
00077    unsigned char remote_key[SRTP_MASTER_LEN];
00078 
00079    if (!ast_rtp_engine_srtp_is_registered()) {
00080       return NULL;
00081    }
00082 
00083    if (!(p = sdp_crypto_alloc())) {
00084       return NULL;
00085    }
00086 
00087    if (res_srtp->get_random(p->local_key, sizeof(p->local_key)) < 0) {
00088       sdp_crypto_destroy(p);
00089       return NULL;
00090    }
00091 
00092    ast_base64encode(p->local_key64, p->local_key, SRTP_MASTER_LEN, sizeof(p->local_key64));
00093 
00094    key_len = ast_base64decode(remote_key, p->local_key64, sizeof(remote_key));
00095 
00096    if (key_len != SRTP_MASTER_LEN) {
00097       ast_log(LOG_ERROR, "base64 encode/decode bad len %d != %d\n", key_len, SRTP_MASTER_LEN);
00098       ast_free(p);
00099       return NULL;
00100    }
00101 
00102    if (memcmp(remote_key, p->local_key, SRTP_MASTER_LEN)) {
00103       ast_log(LOG_ERROR, "base64 encode/decode bad key\n");
00104       ast_free(p);
00105       return NULL;
00106    }
00107 
00108    ast_debug(1 , "local_key64 %s len %zu\n", p->local_key64, strlen(p->local_key64));
00109 
00110    return p;
00111 }
00112 
00113 static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound)
00114 {
00115    const unsigned char *master_salt = NULL;
00116 
00117    if (!ast_rtp_engine_srtp_is_registered()) {
00118       return -1;
00119    }
00120 
00121    master_salt = master_key + SRTP_MASTERKEY_LEN;
00122    if (res_srtp_policy->set_master_key(policy, master_key, SRTP_MASTERKEY_LEN, master_salt, SRTP_MASTERSALT_LEN) < 0) {
00123       return -1;
00124    }
00125 
00126    if (res_srtp_policy->set_suite(policy, suite_val)) {
00127       ast_log(LOG_WARNING, "Could not set remote SRTP suite\n");
00128       return -1;
00129    }
00130 
00131    res_srtp_policy->set_ssrc(policy, ssrc, inbound);
00132 
00133    return 0;
00134 }
00135 
00136 static int sdp_crypto_activate(struct sdp_crypto *p, int suite_val, unsigned char *remote_key, struct ast_rtp_instance *rtp)
00137 {
00138    struct ast_srtp_policy *local_policy = NULL;
00139    struct ast_srtp_policy *remote_policy = NULL;
00140    struct ast_rtp_instance_stats stats = {0,};
00141    int res = -1;
00142 
00143    if (!ast_rtp_engine_srtp_is_registered()) {
00144       return -1;
00145    }
00146 
00147    if (!p) {
00148       return -1;
00149    }
00150 
00151    if (!(local_policy = res_srtp_policy->alloc())) {
00152       return -1;
00153    }
00154 
00155    if (!(remote_policy = res_srtp_policy->alloc())) {
00156       goto err;
00157    }
00158 
00159    if (ast_rtp_instance_get_stats(rtp, &stats, AST_RTP_INSTANCE_STAT_LOCAL_SSRC)) {
00160       goto err;
00161    }
00162 
00163    if (set_crypto_policy(local_policy, suite_val, p->local_key, stats.local_ssrc, 0) < 0) {
00164       goto err;
00165    }
00166 
00167    if (set_crypto_policy(remote_policy, suite_val, remote_key, 0, 1) < 0) {
00168       goto err;
00169    }
00170 
00171    /* Add the SRTP policies */
00172    if (ast_rtp_instance_add_srtp_policy(rtp, remote_policy, local_policy)) {
00173       ast_log(LOG_WARNING, "Could not set SRTP policies\n");
00174       goto err;
00175    }
00176 
00177    ast_debug(1 , "SRTP policy activated\n");
00178    res = 0;
00179 
00180 err:
00181    if (local_policy) {
00182       res_srtp_policy->destroy(local_policy);
00183    }
00184 
00185    if (remote_policy) {
00186       res_srtp_policy->destroy(remote_policy);
00187    }
00188 
00189    return res;
00190 }
00191 
00192 int sdp_crypto_process(struct sdp_crypto *p, const char *attr, struct ast_rtp_instance *rtp)
00193 {
00194    char *str = NULL;
00195    char *tag = NULL;
00196    char *suite = NULL;
00197    char *key_params = NULL;
00198    char *key_param = NULL;
00199    char *session_params = NULL;
00200    char *key_salt = NULL;
00201    char *lifetime = NULL;
00202    int found = 0;
00203    int key_len = 0;
00204    int suite_val = 0;
00205    unsigned char remote_key[SRTP_MASTER_LEN];
00206 
00207    if (!ast_rtp_engine_srtp_is_registered()) {
00208       return -1;
00209    }
00210 
00211    str = ast_strdupa(attr);
00212 
00213    strsep(&str, ":");
00214    tag = strsep(&str, " ");
00215    suite = strsep(&str, " ");
00216    key_params = strsep(&str, " ");
00217    session_params = strsep(&str, " ");
00218 
00219    if (!tag || !suite) {
00220       ast_log(LOG_WARNING, "Unrecognized a=%s", attr);
00221       return -1;
00222    }
00223 
00224    if (session_params) {
00225       ast_log(LOG_WARNING, "Unsupported crypto parameters: %s", session_params);
00226       return -1;
00227    }
00228 
00229    if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80")) {
00230       suite_val = AST_AES_CM_128_HMAC_SHA1_80;
00231    } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
00232       suite_val = AST_AES_CM_128_HMAC_SHA1_32;
00233    } else {
00234       ast_log(LOG_WARNING, "Unsupported crypto suite: %s\n", suite);
00235       return -1;
00236    }
00237 
00238    while ((key_param = strsep(&key_params, ";"))) {
00239       char *method = NULL;
00240       char *info = NULL;
00241 
00242       method = strsep(&key_param, ":");
00243       info = strsep(&key_param, ";");
00244 
00245       if (!strcmp(method, "inline")) {
00246          key_salt = strsep(&info, "|");
00247          lifetime = strsep(&info, "|");
00248 
00249          if (lifetime) {
00250             ast_log(LOG_NOTICE, "Crypto life time unsupported: %s\n", attr);
00251             continue;
00252          }
00253 
00254          found = 1;
00255          break;
00256       }
00257    }
00258 
00259    if (!found) {
00260       ast_log(LOG_NOTICE, "SRTP crypto offer not acceptable\n");
00261       return -1;
00262    }
00263 
00264    if ((key_len = ast_base64decode(remote_key, key_salt, sizeof(remote_key))) != SRTP_MASTER_LEN) {
00265       ast_log(LOG_WARNING, "SRTP descriptions key %d != %d\n", key_len, SRTP_MASTER_LEN);
00266       return -1;
00267    }
00268 
00269    if (!memcmp(p->remote_key, remote_key, sizeof(p->remote_key))) {
00270       ast_debug(1, "SRTP remote key unchanged; maintaining current policy\n");
00271       return 0;
00272    }
00273 
00274    /* Set the accepted policy and remote key */
00275    ast_copy_string(p->suite, suite, sizeof(p->suite));
00276    memcpy(p->remote_key, remote_key, sizeof(p->remote_key));
00277 
00278    if (sdp_crypto_activate(p, suite_val, remote_key, rtp) < 0) {
00279       return -1;
00280    }
00281 
00282    if (!p->tag) {
00283       ast_debug(1, "Accepting crypto tag %s\n", tag);
00284       p->tag = ast_strdup(tag);
00285       if (!p->tag) {
00286          ast_log(LOG_ERROR, "Could not allocate memory for tag\n");
00287          return -1;
00288       }
00289    }
00290 
00291    /* Finally, rebuild the crypto line */
00292    return sdp_crypto_offer(p);
00293 }
00294 
00295 int sdp_crypto_offer(struct sdp_crypto *p)
00296 {
00297    if (ast_strlen_zero(p->suite)) {
00298       /* Default crypto offer */
00299       strcpy(p->suite, "AES_CM_128_HMAC_SHA1_80");
00300    }
00301 
00302    /* Rebuild the crypto line */
00303    if (p->a_crypto) {
00304       ast_free(p->a_crypto);
00305    }
00306 
00307    if (ast_asprintf(&p->a_crypto, "a=crypto:%s %s inline:%s\r\n",
00308           p->tag ? p->tag : "1", p->suite, p->local_key64) == -1) {
00309          ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n");
00310       return -1;
00311    }
00312 
00313    ast_debug(1, "Crypto line: %s", p->a_crypto);
00314 
00315    return 0;
00316 }
00317 
00318 const char *sdp_crypto_attrib(struct sdp_crypto *p)
00319 {
00320    return p->a_crypto;
00321 }

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