Thu Oct 11 06:33:55 2012

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: 372712 $")
00035 
00036 #include "asterisk/options.h"
00037 #include "asterisk/utils.h"
00038 #include "include/sdp_crypto.h"
00039 #include "include/srtp.h"
00040 
00041 #define SRTP_MASTER_LEN 30
00042 #define SRTP_MASTERKEY_LEN 16
00043 #define SRTP_MASTERSALT_LEN ((SRTP_MASTER_LEN) - (SRTP_MASTERKEY_LEN))
00044 #define SRTP_MASTER_LEN64 (((SRTP_MASTER_LEN) * 8 + 5) / 6 + 1)
00045 
00046 extern struct ast_srtp_res *res_srtp;
00047 extern struct ast_srtp_policy_res *res_srtp_policy;
00048 
00049 struct sdp_crypto {
00050    char *a_crypto;
00051    unsigned char local_key[SRTP_MASTER_LEN];
00052    char local_key64[SRTP_MASTER_LEN64];
00053    unsigned char remote_key[SRTP_MASTER_LEN];
00054 };
00055 
00056 static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound);
00057 
00058 static struct sdp_crypto *sdp_crypto_alloc(void)
00059 {
00060    return ast_calloc(1, sizeof(struct sdp_crypto));
00061 }
00062 
00063 void sdp_crypto_destroy(struct sdp_crypto *crypto)
00064 {
00065    ast_free(crypto->a_crypto);
00066    crypto->a_crypto = NULL;
00067    ast_free(crypto);
00068 }
00069 
00070 struct sdp_crypto *sdp_crypto_setup(void)
00071 {
00072    struct sdp_crypto *p;
00073    int key_len;
00074    unsigned char remote_key[SRTP_MASTER_LEN];
00075 
00076    if (!ast_rtp_engine_srtp_is_registered()) {
00077       return NULL;
00078    }
00079 
00080    if (!(p = sdp_crypto_alloc())) {
00081       return NULL;
00082    }
00083 
00084    if (res_srtp->get_random(p->local_key, sizeof(p->local_key)) < 0) {
00085       sdp_crypto_destroy(p);
00086       return NULL;
00087    }
00088 
00089    ast_base64encode(p->local_key64, p->local_key, SRTP_MASTER_LEN, sizeof(p->local_key64));
00090 
00091    key_len = ast_base64decode(remote_key, p->local_key64, sizeof(remote_key));
00092 
00093    if (key_len != SRTP_MASTER_LEN) {
00094       ast_log(LOG_ERROR, "base64 encode/decode bad len %d != %d\n", key_len, SRTP_MASTER_LEN);
00095       ast_free(p);
00096       return NULL;
00097    }
00098 
00099    if (memcmp(remote_key, p->local_key, SRTP_MASTER_LEN)) {
00100       ast_log(LOG_ERROR, "base64 encode/decode bad key\n");
00101       ast_free(p);
00102       return NULL;
00103    }
00104 
00105    ast_debug(1 , "local_key64 %s len %zu\n", p->local_key64, strlen(p->local_key64));
00106 
00107    return p;
00108 }
00109 
00110 static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound)
00111 {
00112    const unsigned char *master_salt = NULL;
00113 
00114    if (!ast_rtp_engine_srtp_is_registered()) {
00115       return -1;
00116    }
00117 
00118    master_salt = master_key + SRTP_MASTERKEY_LEN;
00119    if (res_srtp_policy->set_master_key(policy, master_key, SRTP_MASTERKEY_LEN, master_salt, SRTP_MASTERSALT_LEN) < 0) {
00120       return -1;
00121    }
00122 
00123    if (res_srtp_policy->set_suite(policy, suite_val)) {
00124       ast_log(LOG_WARNING, "Could not set remote SRTP suite\n");
00125       return -1;
00126    }
00127 
00128    res_srtp_policy->set_ssrc(policy, ssrc, inbound);
00129 
00130    return 0;
00131 }
00132 
00133 static int sdp_crypto_activate(struct sdp_crypto *p, int suite_val, unsigned char *remote_key, struct ast_rtp_instance *rtp)
00134 {
00135    struct ast_srtp_policy *local_policy = NULL;
00136    struct ast_srtp_policy *remote_policy = NULL;
00137    struct ast_rtp_instance_stats stats = {0,};
00138    int res = -1;
00139 
00140    if (!ast_rtp_engine_srtp_is_registered()) {
00141       return -1;
00142    }
00143 
00144    if (!p) {
00145       return -1;
00146    }
00147 
00148    if (!(local_policy = res_srtp_policy->alloc())) {
00149       return -1;
00150    }
00151 
00152    if (!(remote_policy = res_srtp_policy->alloc())) {
00153       goto err;
00154    }
00155 
00156    if (ast_rtp_instance_get_stats(rtp, &stats, AST_RTP_INSTANCE_STAT_LOCAL_SSRC)) {
00157       goto err;
00158    }
00159 
00160    if (set_crypto_policy(local_policy, suite_val, p->local_key, stats.local_ssrc, 0) < 0) {
00161       goto err;
00162    }
00163 
00164    if (set_crypto_policy(remote_policy, suite_val, remote_key, 0, 1) < 0) {
00165       goto err;
00166    }
00167 
00168    /* Add the SRTP policies */
00169    if (ast_rtp_instance_add_srtp_policy(rtp, remote_policy, local_policy)) {
00170       ast_log(LOG_WARNING, "Could not set SRTP policies\n");
00171       goto err;
00172    }
00173 
00174    ast_debug(1 , "SRTP policy activated\n");
00175    res = 0;
00176 
00177 err:
00178    if (local_policy) {
00179       res_srtp_policy->destroy(local_policy);
00180    }
00181 
00182    if (remote_policy) {
00183       res_srtp_policy->destroy(remote_policy);
00184    }
00185 
00186    return res;
00187 }
00188 
00189 int sdp_crypto_process(struct sdp_crypto *p, const char *attr, struct ast_rtp_instance *rtp, struct sip_srtp *srtp)
00190 {
00191    char *str = NULL;
00192    char *tag = NULL;
00193    char *suite = NULL;
00194    char *key_params = NULL;
00195    char *key_param = NULL;
00196    char *session_params = NULL;
00197    char *key_salt = NULL;
00198    char *lifetime = NULL;
00199    int found = 0;
00200    int attr_len = strlen(attr);
00201    int key_len = 0;
00202    int suite_val = 0;
00203    unsigned char remote_key[SRTP_MASTER_LEN];
00204 
00205    if (!ast_rtp_engine_srtp_is_registered()) {
00206       return -1;
00207    }
00208 
00209    str = ast_strdupa(attr);
00210 
00211    strsep(&str, ":");
00212    tag = strsep(&str, " ");
00213    suite = strsep(&str, " ");
00214    key_params = strsep(&str, " ");
00215    session_params = strsep(&str, " ");
00216 
00217    if (!tag || !suite) {
00218       ast_log(LOG_WARNING, "Unrecognized a=%s", attr);
00219       return -1;
00220    }
00221 
00222    if (!ast_strlen_zero(session_params)) {
00223       ast_log(LOG_WARNING, "Unsupported crypto parameters: %s", session_params);
00224       return -1;
00225    }
00226 
00227    if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80")) {
00228       suite_val = AST_AES_CM_128_HMAC_SHA1_80;
00229       ast_set_flag(srtp, SRTP_CRYPTO_TAG_80);
00230    } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
00231       suite_val = AST_AES_CM_128_HMAC_SHA1_32;
00232       ast_set_flag(srtp, SRTP_CRYPTO_TAG_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    memcpy(p->remote_key, remote_key, sizeof(p->remote_key));
00274 
00275    if (sdp_crypto_activate(p, suite_val, remote_key, rtp) < 0) {
00276       return -1;
00277    }
00278 
00279    if (!p->a_crypto) {
00280       if (!(p->a_crypto = ast_calloc(1, attr_len + 11))) {
00281          ast_log(LOG_ERROR, "Could not allocate memory for a_crypto\n");
00282          return -1;
00283       }
00284       snprintf(p->a_crypto, attr_len + 10, "a=crypto:%s %s inline:%s\r\n", tag, suite, p->local_key64);
00285    }
00286    return 0;
00287 }
00288 
00289 int sdp_crypto_offer(struct sdp_crypto *p, int taglen)
00290 {
00291    char crypto_buf[128];
00292 
00293    if (p->a_crypto) {
00294       ast_free(p->a_crypto);
00295    }
00296 
00297    if (snprintf(crypto_buf, sizeof(crypto_buf), "a=crypto:1 AES_CM_128_HMAC_SHA1_%i inline:%s\r\n",
00298          taglen, p->local_key64) < 1) {
00299       return -1;
00300    }
00301 
00302    if (!(p->a_crypto = ast_strdup(crypto_buf))) {
00303       return -1;
00304    }
00305 
00306    return 0;
00307 }
00308 
00309 const char *sdp_crypto_attrib(struct sdp_crypto *p)
00310 {
00311    return p->a_crypto;
00312 }

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