From 4dcb6aab1f765ac7ad0011736c647d8b809cf8ea Mon Sep 17 00:00:00 2001
From: Richard Fuchs <rfuchs@sipwise.com>
Date: Thu, 27 Jun 2013 09:29:33 -0400
Subject: [PATCH] add compile flag for libsrtp vs rfc srtcp key derivation

---
 daemon/Makefile |  2 ++
 daemon/rtcp.c   | 20 +++++++++++++++++---
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/daemon/Makefile b/daemon/Makefile
index 422e144e5..e985bd2f7 100644
--- a/daemon/Makefile
+++ b/daemon/Makefile
@@ -10,6 +10,8 @@ CFLAGS+=	-D_GNU_SOURCE
 CFLAGS+=	-DMEDIAPROXY_VERSION="\"$(shell dpkg-parsechangelog -l../debian/changelog | awk '/^Version: / {print $$2}')\""
 CFLAGS+=	-DMP_PLUGIN_DIR="\"/usr/lib/mediaproxy-ng\""
 
+#CFLAGS+=	-DSRTCP_KEY_DERIVATION_RFC_COMPLIANCE
+
 ifeq ($(DBG),yes)
 CFLAGS+=	-D__DEBUG=1
 else
diff --git a/daemon/rtcp.c b/daemon/rtcp.c
index d4d0b3e8b..852ac07a2 100644
--- a/daemon/rtcp.c
+++ b/daemon/rtcp.c
@@ -13,6 +13,20 @@
 
 
 
+/* This toggles between two different and incompatible interpretations of
+ * RFC 3711, namely sections 4.3.2 and 4.3.1.
+ * See http://www.ietf.org/mail-archive/web/avt/current/msg06124.html
+ * The default (define not set) is to be compatible with libsrtp, but
+ * incompatible with a strict interpretation of the RFC.
+ */
+#ifdef SRTCP_KEY_DERIVATION_RFC_COMPLIANCE
+#define SRTCP_R_LENGTH 4
+#else
+#define SRTCP_R_LENGTH 6
+#endif
+
+
+
 
 #define RTCP_PT_SR	200	/* sender report */
 #define RTCP_PT_RR	201	/* receiver report */
@@ -323,13 +337,13 @@ static inline int check_session_keys(struct crypto_context *c) {
 		goto error;
 
 	str_init_len(&s, c->session_key, c->crypto_suite->session_key_len);
-	if (crypto_gen_session_key(c, &s, 0x03, 6))
+	if (crypto_gen_session_key(c, &s, 0x03, SRTCP_R_LENGTH))
 		goto error;
 	str_init_len(&s, c->session_auth_key, c->crypto_suite->srtcp_auth_key_len);
-	if (crypto_gen_session_key(c, &s, 0x04, 6))
+	if (crypto_gen_session_key(c, &s, 0x04, SRTCP_R_LENGTH))
 		goto error;
 	str_init_len(&s, c->session_salt, c->crypto_suite->session_salt_len);
-	if (crypto_gen_session_key(c, &s, 0x05, 6))
+	if (crypto_gen_session_key(c, &s, 0x05, SRTCP_R_LENGTH))
 		goto error;
 
 	c->have_session_key = 1;