include/srtp.h

/*
 * 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 <stdint.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 16 

/**
 * 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 

/*
 * SRTP_AEAD_SALT_LEN is the length of the SALT values used with 
 * GCM mode.  GCM mode requires an IV.  The SALT value is used
 * as part of the IV formation logic applied to each RTP packet.
 */
#define SRTP_AEAD_SALT_LEN	12
#define SRTP_AES_128_GCM_KEYSIZE_WSALT   SRTP_AEAD_SALT_LEN + 16
#define SRTP_AES_192_GCM_KEYSIZE_WSALT   SRTP_AEAD_SALT_LEN + 24
#define SRTP_AES_256_GCM_KEYSIZE_WSALT   SRTP_AEAD_SALT_LEN + 32

/*
 * 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

/*
 * srtp_hdr_t represents an RTP or SRTP header.  The bit-fields in
 * this structure should be declared "unsigned int" instead of 
 * "unsigned char", but doing so causes the MS compiler to not
 * fully pack the bit fields.
 */

typedef struct {
  unsigned char cc:4;	/* CSRC count             */
  unsigned char x:1;	/* header extension flag  */
  unsigned char p:1;	/* padding flag           */
  unsigned char version:2; /* protocol version    */
  unsigned char pt:7;	/* payload type           */
  unsigned char 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 char version:2; /* protocol version    */
  unsigned char p:1;	/* padding flag           */
  unsigned char x:1;	/* header extension flag  */
  unsigned char cc:4;	/* CSRC count             */
  unsigned char m:1;	/* marker bit             */
  unsigned char 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



/** 
 *  @brief A srtp_cipher_type_id_t is an identifier for a particular cipher
 *  type.
 *
 *  A srtp_cipher_type_id_t is an integer that represents a particular
 *  cipher type, e.g. the Advanced Encryption Standard (AES).  A
 *  SRTP_NULL_CIPHER is avaliable; this cipher leaves the data unchanged,
 *  and can be selected to indicate that no encryption is to take
 *  place.
 * 
 *  @ingroup Ciphers
 */
typedef uint32_t srtp_cipher_type_id_t; 

/**
 *  @brief An srtp_auth_type_id_t is an identifier for a particular authentication
 *   function.
 *
 *  An srtp_auth_type_id_t is an integer that represents a particular
 *  authentication function type, e.g. HMAC-SHA1.  A SRTP_NULL_AUTH is
 *  avaliable; this authentication function performs no computation,
 *  and can be selected to indicate that no authentication is to take
 *  place.
 *  
 *  @ingroup Authentication
 */
typedef uint32_t srtp_auth_type_id_t;

/*
 * @brief srtp_err_status_t defines error codes.
 *
 * The enumeration srtp_err_status_t defines error codes.  Note that the
 * value of srtp_err_status_ok is equal to zero, which can simplify error
 * checking somewhat.
 *
 */
typedef enum {
  srtp_err_status_ok           = 0,  /**< nothing to report                       */
  srtp_err_status_fail         = 1,  /**< unspecified failure                     */
  srtp_err_status_bad_param    = 2,  /**< unsupported parameter                   */
  srtp_err_status_alloc_fail   = 3,  /**< couldn't allocate memory                */
  srtp_err_status_dealloc_fail = 4,  /**< couldn't deallocate properly            */
  srtp_err_status_init_fail    = 5,  /**< couldn't initialize                     */
  srtp_err_status_terminus     = 6,  /**< can't process as much data as requested */
  srtp_err_status_auth_fail    = 7,  /**< authentication failure                  */
  srtp_err_status_cipher_fail  = 8,  /**< cipher failure                          */
  srtp_err_status_replay_fail  = 9,  /**< replay check failed (bad index)         */
  srtp_err_status_replay_old   = 10, /**< replay check failed (index too old)     */
  srtp_err_status_algo_fail    = 11, /**< algorithm failed test routine           */
  srtp_err_status_no_such_op   = 12, /**< unsupported operation                   */
  srtp_err_status_no_ctx       = 13, /**< no appropriate context found            */
  srtp_err_status_cant_check   = 14, /**< unable to perform desired validation    */
  srtp_err_status_key_expired  = 15, /**< can't use key any more                  */
  srtp_err_status_socket_err   = 16, /**< error in use of socket                  */
  srtp_err_status_signal_err   = 17, /**< error in use POSIX signals              */
  srtp_err_status_nonce_bad    = 18, /**< nonce check failed                      */
  srtp_err_status_read_fail    = 19, /**< couldn't read data                      */
  srtp_err_status_write_fail   = 20, /**< couldn't write data                     */
  srtp_err_status_parse_err    = 21, /**< error parsing data                      */
  srtp_err_status_encode_err   = 22, /**< error encoding data                     */
  srtp_err_status_semaphore_err = 23,/**< error while using semaphores            */
  srtp_err_status_pfkey_err    = 24  /**< error while using pfkey                 */
} srtp_err_status_t;

typedef struct srtp_stream_ctx_t_ srtp_stream_ctx_t;
typedef struct srtp_ctx_t_ srtp_ctx_t;

/* 
 * 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 srtp_sec_serv_t describes a set of security services. 
 *
 * A srtp_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 */
} srtp_sec_serv_t;

/** 
 * @brief srtp_crypto_policy_t describes a particular crypto policy that
 * can be applied to an SRTP stream.
 *
 * A srtp_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 srtp_crypto_policy_t {
  srtp_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.                       */
  srtp_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.                   */
  srtp_sec_serv_t  sec_serv;       /**< The flag indicating the security
				    *   services to be applied.          */
} srtp_crypto_policy_t;


/** 
 * @brief srtp_ssrc_type_t describes the type of an SSRC.
 * 
 * An srtp_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())		  */
} srtp_ssrc_type_t;

/**
 * @brief An srtp_ssrc_t represents a particular SSRC value, or a `wildcard' SSRC.
 * 
 * An srtp_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 { 
  srtp_ssrc_type_t type;  /**< The type of this particular SSRC */
  unsigned int     value; /**< The value of this SSRC, if it is not a wildcard */
} srtp_ssrc_t;


/**
 * @brief points to an EKT policy
 */
typedef struct srtp_ekt_policy_ctx_t *srtp_ekt_policy_t;


/**
 * @brief points to EKT stream data
 */
typedef struct srtp_ekt_stream_ctx_t *srtp_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 {
  srtp_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.
			      */
  srtp_crypto_policy_t rtp;    /**< SRTP crypto policy.                  */
  srtp_crypto_policy_t rtcp;   /**< SRTCP crypto policy.                 */
  unsigned char *key;          /**< Pointer to the SRTP master key for
				*    this stream.                        */
  srtp_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!)                      */
  int *enc_xtn_hdr;            /**< List of header ids to encrypt.       */
  int enc_xtn_hdr_count;       /**< Number of entries in list of header ids. */
  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 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 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.
 */

srtp_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.
 */

srtp_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 srtp_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.
 *
 * @warning This function assumes that it can write SRTP_MAX_TRAILER_LEN 
 * into the location in memory immediately following the RTP packet.   
 * Callers MUST ensure that this much writable memory is available in 
 * the buffer that holds the RTP packet.
 * 
 * @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 srtp_err_status_ok was returned.
 * Otherwise, the value of the data to which it points is undefined.
 *
 * @return 
 *    - srtp_err_status_ok            no problems
 *    - srtp_err_status_replay_fail   rtp sequence number was non-increasing
 *    - @e other                 failure in cryptographic mechanisms
 */

srtp_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
 * srtp_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 the SRTP session 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 srtp_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 srtp_err_status_ok was returned.
 * Otherwise, the value of the data to which it points is undefined.
 *
 * @return 
 *    - srtp_err_status_ok          if the RTP packet is valid.
 *    - srtp_err_status_auth_fail   if the SRTP packet failed the message 
 *                             authentication check.
 *    - srtp_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.
 *
 */

srtp_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) allocates and
 * initializes an SRTP session context, applying the given policy. 
 *
 * @param session is a pointer to 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
 *    - srtp_err_status_ok           if creation succeded.
 *    - srtp_err_status_alloc_fail   if allocation failed.
 *    - srtp_err_status_init_fail    if initialization failed.
 */

srtp_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:
 *    - srtp_err_status_ok           if stream creation succeded.
 *    - srtp_err_status_alloc_fail   if stream allocation failed
 *    - srtp_err_status_init_fail    if stream initialization failed.
 */

srtp_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
 *             in network byte order.
 *
 * @warning Wildcard SSRC values cannot be removed from a
 *          session.
 * 
 * @return
 *    - srtp_err_status_ok     if the stream deallocation succeded.
 *    - [other]           otherwise.
 *
 */

srtp_err_status_t srtp_remove_stream(srtp_t session, unsigned int ssrc);

/**
 * @brief srtp_update() udpates all streams in the session.
 *
 * The function call srtp_update(session, policy) updates
 * all the streams in the session applying the given policy
 * and key. The exsisting ROC value of all streams will be
 * preserved.
 *
 * @param session is the SRTP session that contains the streams
 *        to be updated.
 *
 * @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. The final element of the list @b must
 * have its `next' field set to NULL.
 *
 * @return
 *    - srtp_err_status_ok           if stream creation succeded.
 *    - srtp_err_status_alloc_fail   if stream allocation failed
 *    - srtp_err_status_init_fail    if stream initialization failed.
 *    - [other]                 otherwise.
 *
 */

srtp_err_status_t srtp_update(srtp_t session, const srtp_policy_t *policy);

/**
 * @brief srtp_update_stream() udpates a SRTP stream.
 *
 * The function call srtp_update_stream(session, policy) updates
 * the stream(s) in the session that match applying the given
 * policy and key. The exsisting ROC value of all stream(s) will
 * be preserved.
 *
 * @param session is the SRTP session that contains the streams
 *        to be updated.
 *
 * @param policy is the srtp_policy_t struct that describes the policy
 * for the session.
 *
 * @return
 *    - srtp_err_status_ok           if stream creation succeded.
 *    - srtp_err_status_alloc_fail   if stream allocation failed
 *    - srtp_err_status_init_fail    if stream initialization failed.
 *    - [other]                      otherwise.
 *
 */

srtp_err_status_t srtp_update_stream(srtp_t session, const srtp_policy_t *policy);

/**
 * @brief srtp_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 srtp_crypto_policy_set_rtp_default(srtp_crypto_policy_t *p);

/**
 * @brief srtp_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 srtp_crypto_policy_set_rtcp_default(&p) sets the
 * srtp_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 srtp_crypto_policy_t datatype.
 * 
 * @return void.
 * 
 */

void srtp_crypto_policy_set_rtcp_default(srtp_crypto_policy_t *p);

/**
 * @brief srtp_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 srtp_crypto_policy_set_aes_cm_128_hmac_sha1_80() is a
 * synonym for srtp_crypto_policy_set_rtp_default().  It conforms to the
 * naming convention used in RFC 4568 (SDP Security Descriptions for
 * Media Streams).
 * 
 * @return void.
 * 
 */

#define srtp_crypto_policy_set_aes_cm_128_hmac_sha1_80(p) srtp_crypto_policy_set_rtp_default(p)


/**
 * @brief srtp_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 srtp_crypto_policy_set_aes_cm_128_hmac_sha1_32(&p)
 * sets the srtp_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 srtp_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 srtp_crypto_policy_set_aes_cm_128_hmac_sha1_32(srtp_crypto_policy_t *p);



/**
 * @brief srtp_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 srtp_crypto_policy_set_aes_cm_128_null_auth(&p) sets
 * the srtp_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 srtp_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 srtp_crypto_policy_set_aes_cm_128_null_auth(srtp_crypto_policy_t *p);


/**
 * @brief srtp_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 srtp_crypto_policy_set_null_cipher_hmac_sha1_80(&p)
 * sets the srtp_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 srtp_crypto_policy_t datatype.
 *
 * @warning This policy is NOT RECOMMENDED for SRTP unless there is a
 * requirement to forego encryption.  
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_null_cipher_hmac_sha1_80(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_null_cipher_hmac_null() sets a crypto
 * policy structure to use no encryption or authentication. 
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_null_cipher_hmac_null(&p)
 * sets the srtp_crypto_policy_t at location p to use no encryption and
 * no authentication.  This policy should only be used for testing and
 * troubleshootingl. 
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @warning This policy is NOT RECOMMENDED for SRTP unless there is a
 * requirement to forego encryption and authentication.  
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_null_cipher_hmac_null(srtp_crypto_policy_t *p);


/**
 * @brief srtp_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 srtp_crypto_policy_set_aes_cm_256_hmac_sha1_80(&p)
 * sets the srtp_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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */

void srtp_crypto_policy_set_aes_cm_256_hmac_sha1_80(srtp_crypto_policy_t *p);


/**
 * @brief srtp_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 srtp_crypto_policy_set_aes_cm_256_hmac_sha1_32(&p)
 * sets the srtp_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 srtp_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 srtp_crypto_policy_set_aes_cm_256_hmac_sha1_32(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_cm_256_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 srtp_crypto_policy_set_aes_cm_256_null_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-256 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 srtp_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 srtp_crypto_policy_set_aes_cm_256_null_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_128_8_auth() sets a crypto
 * policy structure to an AEAD encryption policy.
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_128_8_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-128 Galois Counter Mode) with 8 octet auth tag.  This
 * policy applies confidentiality and authentication to both the
 * RTP and RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_128_8_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_256_8_auth() sets a crypto
 * policy structure to an AEAD encryption policy
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_256_8_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-256 Galois Counter Mode) with 8 octet auth tag.  This 
 * policy applies confidentiality and authentication to both the
 * RTP and RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_256_8_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_128_8_only_auth() sets a crypto
 * policy structure to an AEAD authentication-only policy
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_128_8_only_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-128 Galois Counter Mode) with 8 octet auth tag.  This policy 
 * applies confidentiality and authentication to the RTP packets, 
 * but only authentication to the RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_128_8_only_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_256_8_only_auth() sets a crypto
 * policy structure to an AEAD authentication-only policy
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_256_8_only_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-256 Galois Counter Mode) with 8 octet auth tag.  This policy 
 * applies confidentiality and authentication to the RTP packets, 
 * but only authentication to the RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_256_8_only_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_128_16_auth() sets a crypto
 * policy structure to an AEAD encryption policy.
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_128_16_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-128 Galois Counter Mode) with 16 octet auth tag.  This
 * policy applies confidentiality and authentication to both the
 * RTP and RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_128_16_auth(srtp_crypto_policy_t *p);

/**
 * @brief srtp_crypto_policy_set_aes_gcm_256_16_auth() sets a crypto
 * policy structure to an AEAD encryption policy
 *
 * @param p is a pointer to the policy structure to be set 
 * 
 * The function call srtp_crypto_policy_set_aes_gcm_256_16_auth(&p) sets
 * the srtp_crypto_policy_t at location p to use the SRTP default cipher
 * (AES-256 Galois Counter Mode) with 16 octet auth tag.  This 
 * policy applies confidentiality and authentication to both the
 * RTP and RTCP packets.
 * 
 * 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 srtp_crypto_policy_t datatype.
 *
 * @return void.
 * 
 */
void srtp_crypto_policy_set_aes_gcm_256_16_auth(srtp_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
 *    - srtp_err_status_ok             if there no problems.
 *    - srtp_err_status_dealloc_fail   a memory deallocation failure occured.
 */

srtp_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 srtp_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 srtp_crypto_policy_set_rtp_default(&policy, profile)
 * sets the srtp_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 srtp_crypto_policy_t datatype.
 * 
 * @return values
 *     - srtp_err_status_ok         no problems were encountered
 *     - srtp_err_status_bad_param  the profile is not supported 
 * 
 */
srtp_err_status_t srtp_crypto_policy_set_from_profile_for_rtp(srtp_crypto_policy_t *policy, srtp_profile_t profile);




/**
 * @brief srtp_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 srtp_crypto_policy_set_rtcp_default(&policy, profile)
 * sets the srtp_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 srtp_crypto_policy_t datatype.
 * 
 * @return values
 *     - srtp_err_status_ok         no problems were encountered
 *     - srtp_err_status_bad_param  the profile is not supported 
 * 
 */
srtp_err_status_t srtp_crypto_policy_set_from_profile_for_rtcp(srtp_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 srtp_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
srtp_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 srtp_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.
 *
 * @warning This function assumes that it can write SRTP_MAX_TRAILER_LEN+4 
 * into the location in memory immediately following the RTCP packet.   
 * Callers MUST ensure that this much writable memory is available in 
 * the buffer that holds the RTCP packet.
 * 
 * @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 srtp_err_status_ok
 * was returned.  Otherwise, the value of the data to which it points
 * is undefined.
 *
 * @return 
 *    - srtp_err_status_ok            if there were no problems.
 *    - [other]                  if there was a failure in 
 *                               the cryptographic mechanisms.
 */
	     

srtp_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 srtp_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 srtp_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 srtp_err_status_ok was
 * returned.  Otherwise, the value of the data to which it points is
 * undefined.
 *
 * @return 
 *    - srtp_err_status_ok          if the RTCP packet is valid.
 *    - srtp_err_status_auth_fail   if the SRTCP packet failed the message 
 *                             authentication check.
 *    - srtp_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.
 *
 */

srtp_err_status_t srtp_unprotect_rtcp(srtp_t ctx, void *srtcp_hdr, int *pkt_octet_len);

/**
 * @}
 */


/**
 * @defgroup User data associated to a SRTP session.
 * @ingroup  SRTP
 *
 * @brief Store custom user data within a SRTP session.
 *
 * @{
 */

/**
 * @brief srtp_set_user_data() stores the given pointer into the SRTP
 * session for later retrieval.
 *
 * @param ctx is the srtp_t context in which the given data pointer is
 * stored.
 *
 * @param data is a pointer to the custom information (struct, function,
 * etc) associated with the SRTP session.
 *
 * @return void.
 *
 */

void
srtp_set_user_data(srtp_t ctx, void *data);

/**
 * @brief srtp_get_user_data() retrieves the pointer to the custom data
 * previously stored with srtp_set_user_data().
 *
 * This function is mostly useful for retrieving data associated to a
 * SRTP session when an event fires. The user can then get such a custom
 * data by calling this function with the session field of the
 * srtp_event_data_t struct as argument.
 *
 * @param ctx is the srtp_t context in which the given data pointer was
 * stored.
 *
 * @return void* pointer to the user data.
 *
 */

void*
srtp_get_user_data(srtp_t ctx);

/**
 * @}
 */


/**
 * @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_remove_stream()), 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.
 */

srtp_err_status_t srtp_install_event_handler(srtp_event_handler_func_t func);

/**
 * @brief Returns the version string of the library. 
 * 
 */
const char *srtp_get_version_string(void);

/**
 * @brief Returns the numeric representation of the library version. 
 * 
 */
unsigned int srtp_get_version(void);

/**
 * @brief srtp_set_debug_module(mod_name, v)
 * 
 * sets dynamic debugging to the value v (0 for off, 1 for on) for the
 * debug module with the name mod_name
 *
 * returns err_status_ok on success, err_status_fail otherwise
 */
srtp_err_status_t srtp_set_debug_module(char *mod_name, int v);

/**
 * @brief srtp_list_debug_modules() outputs a list of debugging modules
 *
 */
srtp_err_status_t srtp_list_debug_modules(void);


/**
 * @}
 */
/* 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 */