Add SRTP support for Asterisk

After 5 years in mantis and over a year on reviewboard, SRTP support is finally
being comitted. This includes generic CHANNEL dialplan functions that work for
getting the status of whether a call has secure media or signaling as defined
by the underlying channel technology and for setting whether or not a new
channel being bridged to a calling channel should have secure signaling or
media. See doc/tex/secure-calls.tex for examples.

Original patch by mikma, updated for trunk and revised by me.

(closes issue #5413)
Reported by: mikma
Tested by: twilson, notthematrix, hemanshurpatel

Review: https://reviewboard.asterisk.org/r/191/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@268894 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sip/include/sdp_crypto.h

@@ -0,0 +1,82 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2006 - 2007, Mikael Magnusson
+ *
+ * Mikael Magnusson <mikma@users.sourceforge.net>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file sdp_crypto.h
+ *
+ * \brief SDP Security descriptions
+ *
+ * Specified in RFC 4568
+ *
+ * \author Mikael Magnusson <mikma@users.sourceforge.net>
+ */
+
+#ifndef _SDP_CRYPTO_H
+#define _SDP_CRYPTO_H
+
+#include <asterisk/rtp_engine.h>
+
+struct sdp_crypto;
+
+/*! \brief Initialize an return an sdp_crypto struct
+ *
+ * \details
+ * This function allocates a new sdp_crypto struct and initializes its values
+ *
+ * \retval NULL on failure
+ * \retval a pointer to a  new sdp_crypto structure
+ */
+struct sdp_crypto *sdp_crypto_setup(void);
+
+/*! \brief Destroy a previously allocated sdp_crypto struct */
+void sdp_crypto_destroy(struct sdp_crypto *crypto);
+
+/*! \brief Parse the a=crypto line from SDP and set appropriate values on the
+ * sdp_crypto struct.
+ *
+ * \param p A valid sdp_crypto struct
+ * \param attr the a:crypto line from SDP
+ * \param rtp The rtp instance associated with the SDP being parsed
+ *
+ * \retval 0 success
+ * \retval nonzero failure
+ */
+int sdp_crypto_process(struct sdp_crypto *p, const char *attr, struct ast_rtp_instance *rtp);
+
+
+/*! \brief Generate an SRTP a=crypto offer
+ *
+ * \details
+ * The offer is stored on the sdp_crypto struct in a_crypto
+ *
+ * \param A valid sdp_crypto struct
+ *
+ * \retval 0 success
+ * \retval nonzero failure
+ */
+int sdp_crypto_offer(struct sdp_crypto *p);
+
+
+/*! \brief Return the a_crypto value of the sdp_crypto struct
+ *
+ * \param p An sdp_crypto struct that has had sdp_crypto_offer called
+ *
+ * \retval The value of the a_crypto for p
+ */
+const char *sdp_crypto_attrib(struct sdp_crypto *p);
+
+#endif	/* _SDP_CRYPTO_H */