rtcp has a slightly different key generation algorithm

daemon/crypto.c

@@ -184,7 +184,7 @@ static void prf_n(str *out, char *key, char *x) {
 
 
 /* rfc 3711 section 4.3.1 */
-int crypto_gen_session_key(struct crypto_context *c, str *out, unsigned char label) {
+int crypto_gen_session_key(struct crypto_context *c, str *out, unsigned char label, int index_len) {
 	unsigned char key_id[7]; /* [ label, 48-bit ROC || SEQ ] */
 	unsigned char x[14];
 	int i;
@@ -193,13 +193,13 @@ int crypto_gen_session_key(struct crypto_context *c, str *out, unsigned char lab
 		return -1;
 
 	ZERO(key_id);
-	/* key_id[1..6] := r
+	/* key_id[1..6] := r; or 1..4 for rtcp
 	 * key_derivation_rate == 0 --> r == 0 */
 
 	key_id[0] = label;
 	memcpy(x, c->master_salt, 14);
-	for (i = 7; i < 14; i++)
-		x[i] = key_id[i - 7] ^ x[i];
+	for (i = 13 - index_len; i < 14; i++)
+		x[i] = key_id[i - (13 - index_len)] ^ x[i];
 
 	prf_n(out, c->master_key, (char *) x);
 
@@ -268,20 +268,3 @@ static int hmac_sha1_rtcp(struct crypto_context *c, char *out, str *in) {
 
 	return 0;
 }
-
-int crypto_gen_session_keys(struct crypto_context *c) {
-	str s;
-
-	str_init_len(&s, c->session_key, c->crypto_suite->session_key_len);
-	if (crypto_gen_session_key(c, &s, 0x00))
-		return -1;
-	str_init_len(&s, c->session_auth_key, c->crypto_suite->srtp_auth_key_len);
-	if (crypto_gen_session_key(c, &s, 0x01))
-		return -1;
-	str_init_len(&s, c->session_salt, c->crypto_suite->session_salt_len);
-	if (crypto_gen_session_key(c, &s, 0x02))
-		return -1;
-
-	c->have_session_key = 1;
-	return 0;
-}

daemon/crypto.h

@@ -94,8 +94,7 @@ extern const int num_crypto_suites;
 
 
 const struct crypto_suite *crypto_find_suite(const str *);
-int crypto_gen_session_keys(struct crypto_context *c);
-int crypto_gen_session_key(struct crypto_context *, str *, unsigned char);
+int crypto_gen_session_key(struct crypto_context *, str *, unsigned char, int);
 
 static inline int crypto_encrypt_rtp(struct crypto_context *c, struct rtp_header *rtp,
 		str *payload, u_int64_t index)
@@ -117,13 +116,6 @@ static inline int crypto_decrypt_rtcp(struct crypto_context *c, struct rtcp_pack
 {
 	return c->crypto_suite->decrypt_rtcp(c, rtcp, payload, index);
 }
-static inline int crypto_check_session_keys(struct crypto_context *c) {
-	if (c->have_session_key)
-		return 0;
-	if (!c->crypto_suite)
-		return -1;
-	return crypto_gen_session_keys(c);
-}
 
 
 

daemon/rtcp.c

@@ -313,6 +313,28 @@ int rtcp_avpf2avp(str *s) {
 }
 
 
+static inline int check_session_keys(struct crypto_context *c) {
+	str s;
+
+	if (c->have_session_key)
+		return 0;
+	if (!c->crypto_suite)
+		return -1;
+
+	str_init_len(&s, c->session_key, c->crypto_suite->session_key_len);
+	if (crypto_gen_session_key(c, &s, 0x03, 4))
+		return -1;
+	str_init_len(&s, c->session_auth_key, c->crypto_suite->srtcp_auth_key_len);
+	if (crypto_gen_session_key(c, &s, 0x04, 4))
+		return -1;
+	str_init_len(&s, c->session_salt, c->crypto_suite->session_salt_len);
+	if (crypto_gen_session_key(c, &s, 0x05, 4))
+		return -1;
+
+	c->have_session_key = 1;
+	return 0;
+}
+
 static int rtcp_payload(struct rtcp_packet **out, str *p, const str *s) {
 	struct rtcp_packet *rtcp;
 
@@ -342,7 +364,7 @@ int rtcp_avp2savp(str *s, struct crypto_context *c) {
 
 	if (rtcp_payload(&rtcp, &payload, s))
 		return -1;
-	if (crypto_check_session_keys(c))
+	if (check_session_keys(c))
 		return -1;
 
 	if (crypto_encrypt_rtcp(c, rtcp, &payload, c->num_packets))
@@ -372,7 +394,7 @@ int rtcp_savp2avp(str *s, struct crypto_context *c) {
 
 	if (rtcp_payload(&rtcp, &payload, s))
 		return -1;
-	if (crypto_check_session_keys(c))
+	if (check_session_keys(c))
 		return -1;
 
 	if (srtp_payloads(&to_auth, &to_decrypt, &auth_tag, NULL,

daemon/rtp.c

@@ -10,6 +10,28 @@
 
 
 
+static inline int check_session_keys(struct crypto_context *c) {
+	str s;
+
+	if (c->have_session_key)
+		return 0;
+	if (!c->crypto_suite)
+		return -1;
+
+	str_init_len(&s, c->session_key, c->crypto_suite->session_key_len);
+	if (crypto_gen_session_key(c, &s, 0x00, 6))
+		return -1;
+	str_init_len(&s, c->session_auth_key, c->crypto_suite->srtp_auth_key_len);
+	if (crypto_gen_session_key(c, &s, 0x01, 6))
+		return -1;
+	str_init_len(&s, c->session_salt, c->crypto_suite->session_salt_len);
+	if (crypto_gen_session_key(c, &s, 0x02, 6))
+		return -1;
+
+	c->have_session_key = 1;
+	return 0;
+}
+
 static int rtp_payload(struct rtp_header **out, str *p, const str *s) {
 	struct rtp_header *rtp;
 	struct rtp_extension *ext;
@@ -111,7 +133,7 @@ int rtp_avp2savp(str *s, struct crypto_context *c) {
 
 	if (rtp_payload(&rtp, &payload, s))
 		return -1;
-	if (crypto_check_session_keys(c))
+	if (check_session_keys(c))
 		return -1;
 
 	index = packet_index(c, rtp);
@@ -142,7 +164,7 @@ int rtp_savp2avp(str *s, struct crypto_context *c) {
 
 	if (rtp_payload(&rtp, &payload, s))
 		return -1;
-	if (crypto_check_session_keys(c))
+	if (check_session_keys(c))
 		return -1;
 
 	index = packet_index(c, rtp);