Add RFC5764 - SRTP key generation during DTLS handshake
Signed-off-by: Johan Pascal <johan.pascal@belledonne-communications.com>
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 083b720..f392c50 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -756,6 +756,79 @@
}
#endif /* MBEDTLS_SSL_ALPN */
+#if defined (MBEDTLS_SSL_DTLS_SRTP)
+static void ssl_write_use_srtp_ext( mbedtls_ssl_context *ssl,
+ unsigned char *buf, size_t *olen )
+{
+ unsigned char *p = buf;
+ size_t protection_profiles_index = 0;
+
+ *olen = 0;
+
+ if( (ssl->dtls_srtp_profiles_list == NULL) || (ssl->dtls_srtp_profiles_list_len == 0) )
+ {
+ return;
+ }
+
+ MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding use_srtp extension" ) );
+
+ *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_USE_SRTP >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_USE_SRTP ) & 0xFF );
+
+ /* RFC5764 section 4.1.1
+ * uint8 SRTPProtectionProfile[2];
+ *
+ * struct {
+ * SRTPProtectionProfiles SRTPProtectionProfiles;
+ * opaque srtp_mki<0..255>;
+ * } UseSRTPData;
+
+ * SRTPProtectionProfile SRTPProtectionProfiles<2..2^16-1>;
+ *
+ * Note: srtp_mki is not supported
+ */
+
+ /* Extension length = 2bytes for profiles lenght, ssl->dtls_srtp_profiles_list_len*2 (each profile is 2 bytes length ) + 1 byte for the non implemented srtp_mki vector length (always 0) */
+ *p++ = (unsigned char)( ( ( 2 + 2*(ssl->dtls_srtp_profiles_list_len) + 1 ) >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( ( 2 + 2*(ssl->dtls_srtp_profiles_list_len) + 1 ) ) & 0xFF );
+
+
+ /* protection profile length: 2*(ssl->dtls_srtp_profiles_list_len) */
+ *p++ = (unsigned char)( ( ( 2*(ssl->dtls_srtp_profiles_list_len) ) >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( 2*(ssl->dtls_srtp_profiles_list_len) ) & 0xFF );
+
+ for( protection_profiles_index=0; protection_profiles_index < ssl->dtls_srtp_profiles_list_len; protection_profiles_index++ )
+ {
+ switch (ssl->dtls_srtp_profiles_list[protection_profiles_index]) {
+ case MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_80:
+ *p++ = ( ( ( MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_80_IANA_VALUE ) >> 8 ) & 0xFF);
+ *p++ = ( ( MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_80_IANA_VALUE ) & 0xFF);
+ break;
+ case MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_32:
+ *p++ = ( ( ( MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_32_IANA_VALUE ) >> 8 ) & 0xFF);
+ *p++ = ( ( MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_32_IANA_VALUE ) & 0xFF);
+ break;
+ case MBEDTLS_SRTP_NULL_HMAC_SHA1_80:
+ *p++ = ( ( ( MBEDTLS_SRTP_NULL_HMAC_SHA1_80_IANA_VALUE ) >> 8 ) & 0xFF);
+ *p++ = ( ( MBEDTLS_SRTP_NULL_HMAC_SHA1_80_IANA_VALUE ) & 0xFF);
+ break;
+ case MBEDTLS_SRTP_NULL_HMAC_SHA1_32:
+ *p++ = ( ( ( MBEDTLS_SRTP_NULL_HMAC_SHA1_32_IANA_VALUE ) >> 8 ) & 0xFF);
+ *p++ = ( ( MBEDTLS_SRTP_NULL_HMAC_SHA1_32_IANA_VALUE ) & 0xFF);
+ break;
+ default:
+ /* Note: we shall never arrive here as protection profiles is checked by ssl_set_dtls_srtp_protection_profiles function */
+ MBEDTLS_SSL_DEBUG_MSG( 1, ( "client hello, ignore illegal DTLS-SRTP protection profile %d", ssl->dtls_srtp_profiles_list[protection_profiles_index]) );
+ break;
+ }
+ }
+
+ *p++ = 0x00; /* non implemented srtp_mki vector length is always 0 */
+ /* total extension length: extension type (2 bytes) + extension length (2 bytes) + protection profile length (2 bytes) + 2*nb protection profiles + srtp_mki vector length(1 byte)*/
+ *olen = 2 + 2 + 2 + 2*(ssl->dtls_srtp_profiles_list_len) + 1;
+}
+#endif /* MBEDTLS_SSL_DTLS_SRTP */
+
/*
* Generate random bytes for ClientHello
*/
@@ -1277,6 +1350,11 @@
ext_len += olen;
#endif
+#if defined(MBEDTLS_SSL_DTLS_SRTP)
+ ssl_write_use_srtp_ext( ssl, p + 2 + ext_len, &olen );
+ ext_len += olen;
+#endif
+
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
if( ( ret = ssl_write_session_ticket_ext( ssl, p + 2 + ext_len,
end, &olen ) ) != 0 )
@@ -1710,6 +1788,81 @@
}
#endif /* MBEDTLS_SSL_ALPN */
+#if defined(MBEDTLS_SSL_DTLS_SRTP)
+static int ssl_parse_use_srtp_ext( mbedtls_ssl_context *ssl,
+ const unsigned char *buf, size_t len )
+{
+ enum mbedtls_DTLS_SRTP_protection_profiles server_protection = MBEDTLS_SRTP_UNSET_PROFILE;
+ size_t i;
+ uint16_t server_protection_profile_value = 0;
+
+ /* If use_srtp is not configured, just ignore the extension */
+ if( ( ssl->dtls_srtp_profiles_list == NULL ) || ( ssl->dtls_srtp_profiles_list_len == 0 ) )
+ return( 0 );
+
+ /* RFC5764 section 4.1.1
+ * uint8 SRTPProtectionProfile[2];
+ *
+ * struct {
+ * SRTPProtectionProfiles SRTPProtectionProfiles;
+ * opaque srtp_mki<0..255>;
+ * } UseSRTPData;
+
+ * SRTPProtectionProfile SRTPProtectionProfiles<2..2^16-1>;
+ *
+ * Note: srtp_mki is not supported
+ */
+
+ /* Length is 5 : one protection profile(2 bytes) + length(2 bytes) and potential srtp_mki which won't be parsed */
+ if( len < 5 )
+ return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
+
+ /*
+ * get the server protection profile
+ */
+ if (((uint16_t)(buf[0]<<8 | buf[1])) != 0x0002) { /* protection profile length must be 0x0002 as we must have only one protection profile in server Hello */
+ return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
+ } else {
+ server_protection_profile_value = buf[2]<<8 | buf[3];
+ }
+
+ /*
+ * Check we have the server profile in our list
+ */
+ for( i=0; i < ssl->dtls_srtp_profiles_list_len; i++)
+ {
+ switch ( server_protection_profile_value ) {
+ case MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_80_IANA_VALUE:
+ server_protection = MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_80;
+ break;
+ case MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_32_IANA_VALUE:
+ server_protection = MBEDTLS_SRTP_AES128_CM_HMAC_SHA1_32;
+ break;
+ case MBEDTLS_SRTP_NULL_HMAC_SHA1_80_IANA_VALUE:
+ server_protection = MBEDTLS_SRTP_NULL_HMAC_SHA1_80;
+ break;
+ case MBEDTLS_SRTP_NULL_HMAC_SHA1_32_IANA_VALUE:
+ server_protection = MBEDTLS_SRTP_NULL_HMAC_SHA1_32;
+ break;
+ default:
+ server_protection = MBEDTLS_SRTP_UNSET_PROFILE;
+ break;
+ }
+
+ if (server_protection == ssl->dtls_srtp_profiles_list[i]) {
+ ssl->chosen_dtls_srtp_profile = ssl->dtls_srtp_profiles_list[i];
+ return 0;
+ }
+ }
+
+ /* If we get there, no match was found : server problem, it shall never answer with incompatible profile */
+ ssl->chosen_dtls_srtp_profile = MBEDTLS_SRTP_UNSET_PROFILE;
+ mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+ MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+ return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
+}
+#endif /* MBEDTLS_SSL_DTLS_SRTP */
+
/*
* Parse HelloVerifyRequest. Only called after verifying the HS type.
*/
@@ -2278,6 +2431,16 @@
break;
#endif /* MBEDTLS_SSL_ALPN */
+#if defined(MBEDTLS_SSL_DTLS_SRTP)
+ case MBEDTLS_TLS_EXT_USE_SRTP:
+ MBEDTLS_SSL_DEBUG_MSG( 3, ( "found use_srtp extension" ) );
+
+ if( ( ret = ssl_parse_use_srtp_ext( ssl, ext + 4, ext_size ) ) != 0 )
+ return( ret );
+
+ break;
+#endif /* MBEDTLS_SSL_DTLS_SRTP */
+
default:
MBEDTLS_SSL_DEBUG_MSG( 3,
( "unknown extension found: %d (ignoring)", ext_id ) );