The Tor Browser: comparison netwerk/srtp/src/include/srtp.h

--1:000000000000
+:b91916968a55
+/*
+* srtp.h
+*
+* interface to libsrtp
+*
+* David A. McGrew
+* Cisco Systems, Inc.
+*/
+/*
+*
+* Copyright (c) 2001-2006, Cisco Systems, Inc.
+* All rights reserved.
+*
+* Redistribution and use in source and binary forms, with or without
+* modification, are permitted provided that the following conditions
+* are met:
+*
+*   Redistributions of source code must retain the above copyright
+*   notice, this list of conditions and the following disclaimer.
+*
+*   Redistributions in binary form must reproduce the above
+*   copyright notice, this list of conditions and the following
+*   disclaimer in the documentation and/or other materials provided
+*   with the distribution.
+*
+*   Neither the name of the Cisco Systems, Inc. nor the names of its
+*   contributors may be used to endorse or promote products derived
+*   from this software without specific prior written permission.
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+* OF THE POSSIBILITY OF SUCH DAMAGE.
+*
+*/
+#ifndef SRTP_H
+#define SRTP_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+#include "crypto_kernel.h"
+/**
+* @defgroup SRTP Secure RTP
+*
+* @brief libSRTP provides functions for protecting RTP and RTCP.  See
+* Section @ref Overview for an introduction to the use of the library.
+*
+* @{
+*/
+/*
+* SRTP_MASTER_KEY_LEN is the nominal master key length supported by libSRTP
+*/
+#define SRTP_MASTER_KEY_LEN 30
+/*
+* SRTP_MAX_KEY_LEN is the maximum key length supported by libSRTP
+*/
+#define SRTP_MAX_KEY_LEN      64
+/*
+* SRTP_MAX_TAG_LEN is the maximum tag length supported by libSRTP
+*/
+#define SRTP_MAX_TAG_LEN 12
+/**
+* SRTP_MAX_TRAILER_LEN is the maximum length of the SRTP trailer
+* (authentication tag and MKI) supported by libSRTP.  This value is
+* the maximum number of octets that will be added to an RTP packet by
+* srtp_protect().
+*
+* @brief the maximum number of octets added by srtp_protect().
+*/
+#define SRTP_MAX_TRAILER_LEN SRTP_MAX_TAG_LEN
+/*
+* nota bene: since libSRTP doesn't support the use of the MKI, the
+* SRTP_MAX_TRAILER_LEN value is just the maximum tag length
+*/
+/**
+* @brief sec_serv_t describes a set of security services.
+*
+* A sec_serv_t enumeration is used to describe the particular
+* security services that will be applied by a particular crypto
+* policy (or other mechanism).
+*/
+typedef enum {
+sec_serv_none          = 0, /**< no services                        */
+sec_serv_conf          = 1, /**< confidentiality                    */
+sec_serv_auth          = 2, /**< authentication                     */
+sec_serv_conf_and_auth = 3  /**< confidentiality and authentication */
+} sec_serv_t;
+/**
+* @brief crypto_policy_t describes a particular crypto policy that
+* can be applied to an SRTP stream.
+*
+* A crypto_policy_t describes a particular cryptographic policy that
+* can be applied to an SRTP or SRTCP stream.  An SRTP session policy
+* consists of a list of these policies, one for each SRTP stream
+* in the session.
+*/
+typedef struct crypto_policy_t {
+cipher_type_id_t cipher_type;    /**< An integer representing
+				    *   the type of cipher.  */
+int              cipher_key_len; /**< The length of the cipher key
+				    *   in octets.                       */
+auth_type_id_t   auth_type;      /**< An integer representing the
+				    *   authentication function.         */
+int              auth_key_len;   /**< The length of the authentication
+				    *   function key in octets.          */
+int              auth_tag_len;   /**< The length of the authentication
+				    *   tag in octets.                   */
+sec_serv_t       sec_serv;       /**< The flag indicating the security
+				    *   services to be applied.          */
+} crypto_policy_t;
+/**
+* @brief ssrc_type_t describes the type of an SSRC.
+*
+* An ssrc_type_t enumeration is used to indicate a type of SSRC.  See
+* @ref srtp_policy_t for more informataion.
+*/
+typedef enum {
+ssrc_undefined    = 0,  /**< Indicates an undefined SSRC type. */
+ssrc_specific     = 1,  /**< Indicates a specific SSRC value   */
+ssrc_any_inbound  = 2, /**< Indicates any inbound SSRC value
+			    (i.e. a value that is used in the
+			    function srtp_unprotect())              */
+ssrc_any_outbound = 3  /**< Indicates any outbound SSRC value
+			    (i.e. a value that is used in the
+			    function srtp_protect())		  */
+} ssrc_type_t;
+/**
+* @brief An ssrc_t represents a particular SSRC value, or a `wildcard' SSRC.
+*
+* An ssrc_t represents a particular SSRC value (if its type is
+* ssrc_specific), or a wildcard SSRC value that will match all
+* outbound SSRCs (if its type is ssrc_any_outbound) or all inbound
+* SSRCs (if its type is ssrc_any_inbound).
+*
+*/
+typedef struct {
+ssrc_type_t type;   /**< The type of this particular SSRC */
+unsigned int value; /**< The value of this SSRC, if it is not a wildcard */
+} ssrc_t;
+/**
+* @brief points to an EKT policy
+*/
+typedef struct ekt_policy_ctx_t *ekt_policy_t;
+/**
+* @brief points to EKT stream data
+*/
+typedef struct ekt_stream_ctx_t *ekt_stream_t;
+/**
+* @brief represents the policy for an SRTP session.
+*
+* A single srtp_policy_t struct represents the policy for a single
+* SRTP stream, and a linked list of these elements represents the
+* policy for an entire SRTP session.  Each element contains the SRTP
+* and SRTCP crypto policies for that stream, a pointer to the SRTP
+* master key for that stream, the SSRC describing that stream, or a
+* flag indicating a `wildcard' SSRC value, and a `next' field that
+* holds a pointer to the next element in the list of policy elements,
+* or NULL if it is the last element.
+*
+* The wildcard value SSRC_ANY_INBOUND matches any SSRC from an
+* inbound stream that for which there is no explicit SSRC entry in
+* another policy element.  Similarly, the value SSRC_ANY_OUTBOUND
+* will matches any SSRC from an outbound stream that does not appear
+* in another policy element.  Note that wildcard SSRCs &b cannot be
+* used to match both inbound and outbound traffic.  This restriction
+* is intentional, and it allows libSRTP to ensure that no security
+* lapses result from accidental re-use of SSRC values during key
+* sharing.
+*
+*
+* @warning The final element of the list @b must have its `next' pointer
+*          set to NULL.
+*/
+typedef struct srtp_policy_t {
+ssrc_t        ssrc;        /**< The SSRC value of stream, or the
+			      *   flags SSRC_ANY_INBOUND or
+			      *   SSRC_ANY_OUTBOUND if key sharing
+			      *   is used for this policy element.
+			      */
+crypto_policy_t rtp;         /**< SRTP crypto policy.                  */
+crypto_policy_t rtcp;        /**< SRTCP crypto policy.                 */
+unsigned char *key;          /**< Pointer to the SRTP master key for
+				*    this stream.                        */
+ekt_policy_t ekt;            /**< Pointer to the EKT policy structure
+*   for this stream (if any)             */
+unsigned long window_size;   /**< The window size to use for replay
+				*   protection. */
+int        allow_repeat_tx;  /**< Whether retransmissions of
+				*   packets with the same sequence number
+				*   are allowed.  (Note that such repeated
+				*   transmissions must have the same RTP
+				*   payload, or a severe security weakness
+				*   is introduced!)                      */
+struct srtp_policy_t *next;  /**< Pointer to next stream policy.       */
+} srtp_policy_t;
+/**
+* @brief An srtp_t points to an SRTP session structure.
+*
+* The typedef srtp_t is a pointer to a structure that represents
+* an SRTP session.  This datatype is intentially opaque in
+* order to separate the interface from the implementation.
+*
+* An SRTP session consists of all of the traffic sent to the RTP and
+* RTCP destination transport addresses, using the RTP/SAVP (Secure
+* Audio/Video Profile).  A session can be viewed as a set of SRTP
+* streams, each of which originates with a different participant.
+*/
+typedef struct srtp_ctx_t *srtp_t;
+/**
+* @brief An srtp_stream_t points to an SRTP stream structure.
+*
+* The typedef srtp_stream_t is a pointer to a structure that
+* represents an SRTP stream.  This datatype is intentionally
+* opaque in order to separate the interface from the implementation.
+*
+* An SRTP stream consists of all of the traffic sent to an SRTP
+* session by a single participant.  A session can be viewed as
+* a set of streams.
+*
+*/
+typedef struct srtp_stream_ctx_t *srtp_stream_t;
+/**
+* @brief srtp_init() initializes the srtp library.
+*
+* @warning This function @b must be called before any other srtp
+* functions.
+*/
+err_status_t
+srtp_init(void);
+/**
+* @brief srtp_shutdown() de-initializes the srtp library.
+*
+* @warning No srtp functions may be called after calling this function.
+*/
+err_status_t
+srtp_shutdown(void);
+/**
+* @brief srtp_protect() is the Secure RTP sender-side packet processing
+* function.
+*
+* The function call srtp_protect(ctx, rtp_hdr, len_ptr) applies SRTP
+* protection to the RTP packet rtp_hdr (which has length *len_ptr) using
+* the SRTP context ctx.  If err_status_ok is returned, then rtp_hdr
+* points to the resulting SRTP packet and *len_ptr is the number of
+* octets in that packet; otherwise, no assumptions should be made
+* about the value of either data elements.
+*
+* The sequence numbers of the RTP packets presented to this function
+* need not be consecutive, but they @b must be out of order by less
+* than 2^15 = 32,768 packets.
+*
+* @warning This function assumes that it can write the authentication
+* tag into the location in memory immediately following the RTP
+* packet, and assumes that the RTP packet is aligned on a 32-bit
+* boundary.
+*
+* @param ctx is the SRTP context to use in processing the packet.
+*
+* @param rtp_hdr is a pointer to the RTP packet (before the call); after
+* the function returns, it points to the srtp packet.
+*
+* @param len_ptr is a pointer to the length in octets of the complete
+* RTP packet (header and body) before the function call, and of the
+* complete SRTP packet after the call, if err_status_ok was returned.
+* Otherwise, the value of the data to which it points is undefined.
+*
+* @return
+*    - err_status_ok            no problems
+*    - err_status_replay_fail   rtp sequence number was non-increasing
+*    - @e other                 failure in cryptographic mechanisms
+*/
+err_status_t
+srtp_protect(srtp_t ctx, void *rtp_hdr, int *len_ptr);
+/**
+* @brief srtp_unprotect() is the Secure RTP receiver-side packet
+* processing function.
+*
+* The function call srtp_unprotect(ctx, srtp_hdr, len_ptr) verifies
+* the Secure RTP protection of the SRTP packet pointed to by srtp_hdr
+* (which has length *len_ptr), using the SRTP context ctx.  If
+* err_status_ok is returned, then srtp_hdr points to the resulting
+* RTP packet and *len_ptr is the number of octets in that packet;
+* otherwise, no assumptions should be made about the value of either
+* data elements.
+*
+* The sequence numbers of the RTP packets presented to this function
+* need not be consecutive, but they @b must be out of order by less
+* than 2^15 = 32,768 packets.
+*
+* @warning This function assumes that the SRTP packet is aligned on a
+* 32-bit boundary.
+*
+* @param ctx is a pointer to the srtp_t which applies to the
+* particular packet.
+*
+* @param srtp_hdr is a pointer to the header of the SRTP packet
+* (before the call).  after the function returns, it points to the
+* rtp packet if err_status_ok was returned; otherwise, the value of
+* the data to which it points is undefined.
+*
+* @param len_ptr is a pointer to the length in octets of the complete
+* srtp packet (header and body) before the function call, and of the
+* complete rtp packet after the call, if err_status_ok was returned.
+* Otherwise, the value of the data to which it points is undefined.
+*
+* @return
+*    - err_status_ok          if the RTP packet is valid.
+*    - err_status_auth_fail   if the SRTP packet failed the message
+*                             authentication check.
+*    - err_status_replay_fail if the SRTP packet is a replay (e.g. packet has
+*                             already been processed and accepted).
+*    - [other]  if there has been an error in the cryptographic mechanisms.
+*
+*/
+err_status_t
+srtp_unprotect(srtp_t ctx, void *srtp_hdr, int *len_ptr);
+/**
+* @brief srtp_create() allocates and initializes an SRTP session.
+* The function call srtp_create(session, policy, key) allocates and
+* initializes an SRTP session context, applying the given policy and
+* key.
+*
+* @param session is the SRTP session to which the policy is to be added.
+*
+* @param policy is the srtp_policy_t struct that describes the policy
+* for the session.  The struct may be a single element, or it may be
+* the head of a list, in which case each element of the list is
+* processed.  It may also be NULL, in which case streams should be added
+* later using srtp_add_stream().  The final element of the list @b must
+* have its `next' field set to NULL.
+*
+* @return
+*    - err_status_ok           if creation succeded.
+*    - err_status_alloc_fail   if allocation failed.
+*    - err_status_init_fail    if initialization failed.
+*/
+err_status_t
+srtp_create(srtp_t *session, const srtp_policy_t *policy);
+/**
+* @brief srtp_add_stream() allocates and initializes an SRTP stream
+* within a given SRTP session.
+*
+* The function call srtp_add_stream(session, policy) allocates and
+* initializes a new SRTP stream within a given, previously created
+* session, applying the policy given as the other argument to that
+* stream.
+*
+* @return values:
+*    - err_status_ok           if stream creation succeded.
+*    - err_status_alloc_fail   if stream allocation failed
+*    - err_status_init_fail    if stream initialization failed.
+*/
+err_status_t
+srtp_add_stream(srtp_t session,
+		const srtp_policy_t *policy);
+/**
+* @brief srtp_remove_stream() deallocates an SRTP stream.
+*
+* The function call srtp_remove_stream(session, ssrc) removes
+* the SRTP stream with the SSRC value ssrc from the SRTP session
+* context given by the argument session.
+*
+* @param session is the SRTP session from which the stream
+*        will be removed.
+*
+* @param ssrc is the SSRC value of the stream to be removed.
+*
+* @warning Wildcard SSRC values cannot be removed from a
+*          session.
+*
+* @return
+*    - err_status_ok     if the stream deallocation succeded.
+*    - [other]           otherwise.
+*
+*/
+err_status_t
+srtp_remove_stream(srtp_t session, unsigned int ssrc);
+/**
+* @brief crypto_policy_set_rtp_default() sets a crypto policy
+* structure to the SRTP default policy for RTP protection.
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_rtp_default(&p) sets the
+* crypto_policy_t at location p to the SRTP default policy for RTP
+* protection, as defined in the specification.  This function is a
+* convenience that helps to avoid dealing directly with the policy
+* data structure.  You are encouraged to initialize policy elements
+* with this function call.  Doing so may allow your code to be
+* forward compatible with later versions of libSRTP that include more
+* elements in the crypto_policy_t datatype.
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_rtp_default(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_rtcp_default() sets a crypto policy
+* structure to the SRTP default policy for RTCP protection.
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_rtcp_default(&p) sets the
+* crypto_policy_t at location p to the SRTP default policy for RTCP
+* protection, as defined in the specification.  This function is a
+* convenience that helps to avoid dealing directly with the policy
+* data structure.  You are encouraged to initialize policy elements
+* with this function call.  Doing so may allow your code to be
+* forward compatible with later versions of libSRTP that include more
+* elements in the crypto_policy_t datatype.
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_rtcp_default(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_aes_cm_128_hmac_sha1_80() sets a crypto
+* policy structure to the SRTP default policy for RTP protection.
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function crypto_policy_set_aes_cm_128_hmac_sha1_80() is a
+* synonym for crypto_policy_set_rtp_default().  It conforms to the
+* naming convention used in RFC 4568 (SDP Security Descriptions for
+* Media Streams).
+*
+* @return void.
+*
+*/
+#define crypto_policy_set_aes_cm_128_hmac_sha1_80(p) crypto_policy_set_rtp_default(p)
+/**
+* @brief crypto_policy_set_aes_cm_128_hmac_sha1_32() sets a crypto
+* policy structure to a short-authentication tag policy
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_aes_cm_128_hmac_sha1_32(&p)
+* sets the crypto_policy_t at location p to use policy
+* AES_CM_128_HMAC_SHA1_32 as defined in RFC 4568.
+* This policy uses AES-128
+* Counter Mode encryption and HMAC-SHA1 authentication, with an
+* authentication tag that is only 32 bits long.  This length is
+* considered adequate only for protecting audio and video media that
+* use a stateless playback function.  See Section 7.5 of RFC 3711
+* (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @warning This crypto policy is intended for use in SRTP, but not in
+* SRTCP.  It is recommended that a policy that uses longer
+* authentication tags be used for SRTCP.  See Section 7.5 of RFC 3711
+* (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_aes_cm_128_hmac_sha1_32(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_aes_cm_128_null_auth() sets a crypto
+* policy structure to an encryption-only policy
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_aes_cm_128_null_auth(&p) sets
+* the crypto_policy_t at location p to use the SRTP default cipher
+* (AES-128 Counter Mode), but to use no authentication method.  This
+* policy is NOT RECOMMENDED unless it is unavoidable; see Section 7.5
+* of RFC 3711 (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @warning This policy is NOT RECOMMENDED for SRTP unless it is
+* unavoidable, and it is NOT RECOMMENDED at all for SRTCP; see
+* Section 7.5 of RFC 3711 (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_aes_cm_128_null_auth(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_null_cipher_hmac_sha1_80() sets a crypto
+* policy structure to an authentication-only policy
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_null_cipher_hmac_sha1_80(&p)
+* sets the crypto_policy_t at location p to use HMAC-SHA1 with an 80
+* bit authentication tag to provide message authentication, but to
+* use no encryption.  This policy is NOT RECOMMENDED for SRTP unless
+* there is a requirement to forego encryption.
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @warning This policy is NOT RECOMMENDED for SRTP unless there is a
+* requirement to forego encryption.
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_null_cipher_hmac_sha1_80(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_aes_cm_256_hmac_sha1_80() sets a crypto
+* policy structure to a encryption and authentication policy using AES-256
+* for RTP protection.
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_aes_cm_256_hmac_sha1_80(&p)
+* sets the crypto_policy_t at location p to use policy
+* AES_CM_256_HMAC_SHA1_80 as defined in
+* draft-ietf-avt-srtp-big-aes-03.txt.  This policy uses AES-256
+* Counter Mode encryption and HMAC-SHA1 authentication, with an 80 bit
+* authentication tag.
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @return void.
+*
+*/
+void crypto_policy_set_aes_cm_256_hmac_sha1_80(crypto_policy_t *p);
+/**
+* @brief crypto_policy_set_aes_cm_256_hmac_sha1_32() sets a crypto
+* policy structure to a short-authentication tag policy using AES-256
+* encryption.
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_aes_cm_256_hmac_sha1_32(&p)
+* sets the crypto_policy_t at location p to use policy
+* AES_CM_256_HMAC_SHA1_32 as defined in
+* draft-ietf-avt-srtp-big-aes-03.txt.  This policy uses AES-256
+* Counter Mode encryption and HMAC-SHA1 authentication, with an
+* authentication tag that is only 32 bits long.  This length is
+* considered adequate only for protecting audio and video media that
+* use a stateless playback function.  See Section 7.5 of RFC 3711
+* (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @warning This crypto policy is intended for use in SRTP, but not in
+* SRTCP.  It is recommended that a policy that uses longer
+* authentication tags be used for SRTCP.  See Section 7.5 of RFC 3711
+* (http://www.ietf.org/rfc/rfc3711.txt).
+*
+* @return void.
+*
+*/
+void
+crypto_policy_set_aes_cm_256_hmac_sha1_32(crypto_policy_t *p);
+/**
+* @brief srtp_dealloc() deallocates storage for an SRTP session
+* context.
+*
+* The function call srtp_dealloc(s) deallocates storage for the
+* SRTP session context s.  This function should be called no more
+* than one time for each of the contexts allocated by the function
+* srtp_create().
+*
+* @param s is the srtp_t for the session to be deallocated.
+*
+* @return
+*    - err_status_ok             if there no problems.
+*    - err_status_dealloc_fail   a memory deallocation failure occured.
+*/
+err_status_t
+srtp_dealloc(srtp_t s);
+/*
+* @brief identifies a particular SRTP profile
+*
+* An srtp_profile_t enumeration is used to identify a particular SRTP
+* profile (that is, a set of algorithms and parameters).  These
+* profiles are defined in the DTLS-SRTP draft.
+*/
+typedef enum {
+srtp_profile_reserved           = 0,
+srtp_profile_aes128_cm_sha1_80  = 1,
+srtp_profile_aes128_cm_sha1_32  = 2,
+srtp_profile_aes256_cm_sha1_80  = 3,
+srtp_profile_aes256_cm_sha1_32  = 4,
+srtp_profile_null_sha1_80       = 5,
+srtp_profile_null_sha1_32       = 6,
+} srtp_profile_t;
+/**
+* @brief crypto_policy_set_from_profile_for_rtp() sets a crypto policy
+* structure to the appropriate value for RTP based on an srtp_profile_t
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_rtp_default(&policy, profile)
+* sets the crypto_policy_t at location policy to the policy for RTP
+* protection, as defined by the srtp_profile_t profile.
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @return values
+*     - err_status_ok         no problems were encountered
+*     - err_status_bad_param  the profile is not supported
+*
+*/
+err_status_t
+crypto_policy_set_from_profile_for_rtp(crypto_policy_t *policy,
+				       srtp_profile_t profile);
+/**
+* @brief crypto_policy_set_from_profile_for_rtcp() sets a crypto policy
+* structure to the appropriate value for RTCP based on an srtp_profile_t
+*
+* @param p is a pointer to the policy structure to be set
+*
+* The function call crypto_policy_set_rtcp_default(&policy, profile)
+* sets the crypto_policy_t at location policy to the policy for RTCP
+* protection, as defined by the srtp_profile_t profile.
+*
+* This function is a convenience that helps to avoid dealing directly
+* with the policy data structure.  You are encouraged to initialize
+* policy elements with this function call.  Doing so may allow your
+* code to be forward compatible with later versions of libSRTP that
+* include more elements in the crypto_policy_t datatype.
+*
+* @return values
+*     - err_status_ok         no problems were encountered
+*     - err_status_bad_param  the profile is not supported
+*
+*/
+err_status_t
+crypto_policy_set_from_profile_for_rtcp(crypto_policy_t *policy,
+				       srtp_profile_t profile);
+/**
+* @brief returns the master key length for a given SRTP profile
+*/
+unsigned int
+srtp_profile_get_master_key_length(srtp_profile_t profile);
+/**
+* @brief returns the master salt length for a given SRTP profile
+*/
+unsigned int
+srtp_profile_get_master_salt_length(srtp_profile_t profile);
+/**
+* @brief appends the salt to the key
+*
+* The function call append_salt_to_key(k, klen, s, slen)
+* copies the string s to the location at klen bytes following
+* the location k.
+*
+* @warning There must be at least bytes_in_salt + bytes_in_key bytes
+*          available at the location pointed to by key.
+*
+*/
+void
+append_salt_to_key(unsigned char *key, unsigned int bytes_in_key,
+		   unsigned char *salt, unsigned int bytes_in_salt);
+/**
+* @}
+*/
+/**
+* @defgroup SRTCP Secure RTCP
+* @ingroup  SRTP
+*
+* @brief Secure RTCP functions are used to protect RTCP traffic.
+*
+* RTCP is the control protocol for RTP.  libSRTP protects RTCP
+* traffic in much the same way as it does RTP traffic.  The function
+* srtp_protect_rtcp() applies cryptographic protections to outbound
+* RTCP packets, and srtp_unprotect_rtcp() verifies the protections on
+* inbound RTCP packets.
+*
+* A note on the naming convention: srtp_protect_rtcp() has an srtp_t
+* as its first argument, and thus has `srtp_' as its prefix.  The
+* trailing `_rtcp' indicates the protocol on which it acts.
+*
+* @{
+*/
+/**
+* @brief srtp_protect_rtcp() is the Secure RTCP sender-side packet
+* processing function.
+*
+* The function call srtp_protect_rtcp(ctx, rtp_hdr, len_ptr) applies
+* SRTCP protection to the RTCP packet rtcp_hdr (which has length
+* *len_ptr) using the SRTP session context ctx.  If err_status_ok is
+* returned, then rtp_hdr points to the resulting SRTCP packet and
+* *len_ptr is the number of octets in that packet; otherwise, no
+* assumptions should be made about the value of either data elements.
+*
+* @warning This function assumes that it can write the authentication
+* tag into the location in memory immediately following the RTCP
+* packet, and assumes that the RTCP packet is aligned on a 32-bit
+* boundary.
+*
+* @param ctx is the SRTP context to use in processing the packet.
+*
+* @param rtcp_hdr is a pointer to the RTCP packet (before the call); after
+* the function returns, it points to the srtp packet.
+*
+* @param pkt_octet_len is a pointer to the length in octets of the
+* complete RTCP packet (header and body) before the function call,
+* and of the complete SRTCP packet after the call, if err_status_ok
+* was returned.  Otherwise, the value of the data to which it points
+* is undefined.
+*
+* @return
+*    - err_status_ok            if there were no problems.
+*    - [other]                  if there was a failure in
+*                               the cryptographic mechanisms.
+*/
+err_status_t
+srtp_protect_rtcp(srtp_t ctx, void *rtcp_hdr, int *pkt_octet_len);
+/**
+* @brief srtp_unprotect_rtcp() is the Secure RTCP receiver-side packet
+* processing function.
+*
+* The function call srtp_unprotect_rtcp(ctx, srtp_hdr, len_ptr)
+* verifies the Secure RTCP protection of the SRTCP packet pointed to
+* by srtcp_hdr (which has length *len_ptr), using the SRTP session
+* context ctx.  If err_status_ok is returned, then srtcp_hdr points
+* to the resulting RTCP packet and *len_ptr is the number of octets
+* in that packet; otherwise, no assumptions should be made about the
+* value of either data elements.
+*
+* @warning This function assumes that the SRTCP packet is aligned on a
+* 32-bit boundary.
+*
+* @param ctx is a pointer to the srtp_t which applies to the
+* particular packet.
+*
+* @param srtcp_hdr is a pointer to the header of the SRTCP packet
+* (before the call).  After the function returns, it points to the
+* rtp packet if err_status_ok was returned; otherwise, the value of
+* the data to which it points is undefined.
+*
+* @param pkt_octet_len is a pointer to the length in octets of the
+* complete SRTCP packet (header and body) before the function call,
+* and of the complete rtp packet after the call, if err_status_ok was
+* returned.  Otherwise, the value of the data to which it points is
+* undefined.
+*
+* @return
+*    - err_status_ok          if the RTCP packet is valid.
+*    - err_status_auth_fail   if the SRTCP packet failed the message
+*                             authentication check.
+*    - err_status_replay_fail if the SRTCP packet is a replay (e.g. has
+*                             already been processed and accepted).
+*    - [other]  if there has been an error in the cryptographic mechanisms.
+*
+*/
+err_status_t
+srtp_unprotect_rtcp(srtp_t ctx, void *srtcp_hdr, int *pkt_octet_len);
+/**
+* @}
+*/
+/**
+* @defgroup SRTPevents SRTP events and callbacks
+* @ingroup  SRTP
+*
+* @brief libSRTP can use a user-provided callback function to
+* handle events.
+*
+*
+* libSRTP allows a user to provide a callback function to handle
+* events that need to be dealt with outside of the data plane (see
+* the enum srtp_event_t for a description of these events).  Dealing
+* with these events is not a strict necessity; they are not
+* security-critical, but the application may suffer if they are not
+* handled.  The function srtp_set_event_handler() is used to provide
+* the callback function.
+*
+* A default event handler that merely reports on the events as they
+* happen is included.  It is also possible to set the event handler
+* function to NULL, in which case all events will just be silently
+* ignored.
+*
+* @{
+*/
+/**
+* @brief srtp_event_t defines events that need to be handled
+*
+* The enum srtp_event_t defines events that need to be handled
+* outside the `data plane', such as SSRC collisions and
+* key expirations.
+*
+* When a key expires or the maximum number of packets has been
+* reached, an SRTP stream will enter an `expired' state in which no
+* more packets can be protected or unprotected.  When this happens,
+* it is likely that you will want to either deallocate the stream
+* (using srtp_stream_dealloc()), and possibly allocate a new one.
+*
+* When an SRTP stream expires, the other streams in the same session
+* are unaffected, unless key sharing is used by that stream.  In the
+* latter case, all of the streams in the session will expire.
+*/
+typedef enum {
+event_ssrc_collision,    /**<
+			    * An SSRC collision occured.
+			    */
+event_key_soft_limit,    /**< An SRTP stream reached the soft key
+			    *   usage limit and will expire soon.
+			    */
+event_key_hard_limit,    /**< An SRTP stream reached the hard
+			    *   key usage limit and has expired.
+			    */
+event_packet_index_limit /**< An SRTP stream reached the hard
+			    * packet limit (2^48 packets).
+			    */
+} srtp_event_t;
+/**
+* @brief srtp_event_data_t is the structure passed as a callback to
+* the event handler function
+*
+* The struct srtp_event_data_t holds the data passed to the event
+* handler function.
+*/
+typedef struct srtp_event_data_t {
+srtp_t        session;  /**< The session in which the event happend. */
+srtp_stream_t stream;   /**< The stream in which the event happend.  */
+srtp_event_t  event;    /**< An enum indicating the type of event.   */
+} srtp_event_data_t;
+/**
+* @brief srtp_event_handler_func_t is the function prototype for
+* the event handler.
+*
+* The typedef srtp_event_handler_func_t is the prototype for the
+* event handler function.  It has as its only argument an
+* srtp_event_data_t which describes the event that needs to be handled.
+* There can only be a single, global handler for all events in
+* libSRTP.
+*/
+typedef void (srtp_event_handler_func_t)(srtp_event_data_t *data);
+/**
+* @brief sets the event handler to the function supplied by the caller.
+*
+* The function call srtp_install_event_handler(func) sets the event
+* handler function to the value func.  The value NULL is acceptable
+* as an argument; in this case, events will be ignored rather than
+* handled.
+*
+* @param func is a pointer to a fuction that takes an srtp_event_data_t
+*             pointer as an argument and returns void.  This function
+*             will be used by libSRTP to handle events.
+*/
+err_status_t
+srtp_install_event_handler(srtp_event_handler_func_t func);
+/**
+* @}
+*/
+/* in host order, so outside the #if */
+#define SRTCP_E_BIT      0x80000000
+/* for byte-access */
+#define SRTCP_E_BYTE_BIT 0x80
+#define SRTCP_INDEX_MASK 0x7fffffff
+#ifdef __cplusplus
+}
+#endif
+#endif /* SRTP_H */

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