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srtp.h

/*
 * srtp.h
 *
 * interface to libsrtp
 *
 * David A. McGrew
 * Cisco Systems, Inc.
 */
/*
 *    
 * Copyright (c) 2001-2005, 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"
#include "rdbx.h"
#include "rdb.h"
#include "integers.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().
 */
00092 #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).  
 */

00107 typedef enum {
00108   sec_serv_none          = 0, /**< no services                        */
00109   sec_serv_conf          = 1, /**< confidentiality                    */
00110   sec_serv_auth          = 2, /**< authentication                     */
00111   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.
 */

00124 typedef struct crypto_policy_t {
00125   cipher_type_id_t cipher_type;    /**< An integer representing
                            *   the type of cipher.  */
00127   int              cipher_key_len; /**< The length of the cipher key
                            *   in octets.                       */
00129   auth_type_id_t   auth_type;      /**< An integer representing the
                            *   authentication function.         */
00131   int              auth_key_len;   /**< The length of the authentication 
                            *   function key in octets.          */
00133   int              auth_tag_len;   /**< The length of the authentication 
                            *   tag in octets.                   */
00135   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.
 */

00147 typedef enum { 
00148   ssrc_undefined    = 0,  /**< Indicates an undefined SSRC type. */
00149   ssrc_specific     = 1,  /**< Indicates a specific SSRC value   */
00150   ssrc_any_inbound  = 2, /**< Indicates any inbound SSRC value 
                      (i.e. a value that is used in the
                      function srtp_unprotect())              */
00153   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).  
 *
 */

00168 typedef struct { 
00169   ssrc_type_t type;   /**< The type of this particular SSRC */
00170   uint32_t value;     /**< The value of this SSRC, if it is not a wildcard */
} ssrc_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.
 */

00201 typedef struct srtp_policy_t {
00202   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.
                        */
00207   crypto_policy_t rtp;         /**< SRTP crypto policy.                  */
00208   crypto_policy_t rtcp;        /**< SRTCP crypto policy.                 */
00209   uint8_t *key;                /**< Pointer to the SRTP master key for
                        *    this stream.                        */
00211   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.
 */

00230 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.  
 *
 */
00245 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_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, uint32_t 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
 * http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdescriptions-12.txt
 * 
 * @return void.
 * 
 */

00473 #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
 * draft-ietf-mmusic-sdescriptions-12.txt.  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 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);



/**
 * @}
 */


/*
 * the following declarations are libSRTP internal functions 
 */

/*
 * srtp_get_stream(ssrc) returns a pointer to the stream corresponding
 * to ssrc, or NULL if no stream exists for that ssrc
 */

srtp_stream_t 
srtp_get_stream(srtp_t srtp, uint32_t ssrc);



/*
 * libsrtp internal datatypes 
 */

typedef enum direction_t { 
  dir_unknown       = 0,
  dir_srtp_sender   = 1, 
  dir_srtp_receiver = 2
} direction_t;

/* 
 * an srtp_stream_t has its own SSRC, encryption key, authentication
 * key, sequence number, and replay database
 * 
 * note that the keys might not actually be unique, in which case the
 * cipher_t and auth_t pointers will point to the same structures
 */

typedef struct srtp_stream_ctx_t {
  uint32_t   ssrc;
  cipher_t  *rtp_cipher;
  auth_t    *rtp_auth;
  rdbx_t     rtp_rdbx;
  sec_serv_t rtp_services;
  cipher_t  *rtcp_cipher;
  auth_t    *rtcp_auth;
  rdb_t      rtcp_rdb;
  sec_serv_t rtcp_services;
  key_limit_ctx_t *limit;
  direction_t direction;
  struct srtp_stream_ctx_t *next;   /* linked list of streams */
} srtp_stream_ctx_t;


/*
 * an srtp_ctx_t holds a stream list and a service description
 */

typedef struct srtp_ctx_t {
  srtp_stream_ctx_t *stream_list;     /* linked list of streams            */
  srtp_stream_ctx_t *stream_template; /* act as template for other streams */
} srtp_ctx_t;



/**
 * @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.
 */

00799 typedef enum { 
00800   event_ssrc_collision,    /**<
                      * An SSRC collision occured.             
                      */
00803   event_key_soft_limit,    /**< An SRTP stream reached the soft key
                      *   usage limit and will expire soon.    
                      */
00806   event_key_hard_limit,    /**< An SRTP stream reached the hard 
                      *   key usage limit and has expired.
                      */
00809   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.  
 */

00822 typedef struct srtp_event_data_t {
00823   srtp_t        session;  /**< The session in which the event happend. */
00824   srtp_stream_t stream;   /**< The stream in which the event happend.  */
00825   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.
 */

00839 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);

/**
 * @}
 */

/*
 * srtp_handle_event(srtp, srtm, evnt) calls the event handling
 * function, if there is one.
 *
 * This macro is not included in the documentation as it is 
 * an internal-only function.
 */

#define srtp_handle_event(srtp, strm, evnt)         \
   if(srtp_event_handler) {                         \
      srtp_event_data_t data;                       \
      data.session = srtp;                          \
      data.stream  = strm;                          \
      data.event   = evnt;                          \
      srtp_event_handler(&data);                    \
}   

/*
 * an srtp_hdr_t represents the srtp header
 *
 * in this implementation, an srtp_hdr_t is assumed to be 32-bit aligned
 * 
 * (note that this definition follows that of RFC 1889 Appendix A, but
 * is not identical)
 */
 
#ifndef WORDS_BIGENDIAN

typedef struct {
  unsigned cc:4;  /* CSRC count             */
  unsigned x:1;         /* header extension flag  */
  unsigned p:1;         /* padding flag           */
  unsigned version:2;   /* protocol version       */
  unsigned pt:7;  /* payload type           */
  unsigned m:1;         /* marker bit             */
  uint16_t seq;         /* sequence number        */
  uint32_t ts;          /* timestamp              */
  uint32_t ssrc;  /* synchronization source */
} srtp_hdr_t;

#else /*  BIG_ENDIAN */

typedef struct {
  unsigned version:2;   /* protocol version       */
  unsigned p:1;         /* padding flag           */
  unsigned x:1;         /* header extension flag  */
  unsigned cc:4;  /* CSRC count             */
  unsigned m:1;         /* marker bit             */
  unsigned pt:7;  /* payload type           */
  uint16_t seq;         /* sequence number        */
  uint32_t ts;          /* timestamp              */
  uint32_t ssrc;  /* synchronization source */
} srtp_hdr_t;

#endif

typedef struct {
  uint16_t profile_specific;    /* profile-specific info               */
  uint16_t length;              /* number of 32-bit words in extension */
} srtp_hdr_xtnd_t;


/*
 * srtcp_hdr_t represents a secure rtcp header 
 *
 * in this implementation, an srtcp header is assumed to be 32-bit
 * alinged
 */

#ifndef WORDS_BIGENDIAN

typedef struct {
  unsigned char rc:5;         /* reception report count */
  unsigned char p:1;          /* padding flag           */
  unsigned char version:2;    /* protocol version       */
  unsigned char pt:8;         /* payload type           */
  uint16_t len;               /* length                 */
  uint32_t ssrc;              /* synchronization source */
} srtcp_hdr_t;

typedef struct {
  unsigned int index:31;    /* srtcp packet index in network order! */
  unsigned int e:1;         /* encrypted? 1=yes */
  /* optional mikey/etc go here */
  /* and then the variable-length auth tag */
} srtcp_trailer_t;


#else /*  BIG_ENDIAN */

typedef struct {
  unsigned char version:2;    /* protocol version       */
  unsigned char p:1;          /* padding flag           */
  unsigned char rc:5;         /* reception report count */
  unsigned char pt:8;         /* payload type           */
  uint16_t len;               /* length                 */
  uint32_t ssrc;              /* synchronization source */
} srtcp_hdr_t;

typedef struct {
  unsigned int version:2;  /* protocol version                     */
  unsigned int p:1;        /* padding flag                         */
  unsigned int count:5;    /* varies by packet type                */
  unsigned int pt:8;       /* payload type                         */
  uint16_t length;         /* len of uint32s of packet less header */
} rtcp_common_t;

typedef struct {
  unsigned int e:1;         /* encrypted? 1=yes */
  unsigned int index:31;    /* srtcp packet index */
  /* optional mikey/etc go here */
  /* and then the variable-length auth tag */
} srtcp_trailer_t;

#endif

/* 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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