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srtp.h (71879B)

---

/*
* srtp.h
*
* interface to libsrtp
*
* David A. McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright (c) 2001-2017, 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_SRTP_H
#define SRTP_SRTP_H

#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
* @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_MKI_LEN is the maximum size the MKI could be which is
* 128 bytes
*/
#define SRTP_MAX_MKI_LEN 128

/**
* 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_MAX_MKI_LEN)

/**
* SRTP_SRCTP_INDEX_LEN is the size the SRTCP index which is
* 4 bytes
*/
#define SRTP_SRCTP_INDEX_LEN 4

/**
* SRTP_MAX_SRTCP_TRAILER_LEN is the maximum length of the SRTCP trailer
* (index, authentication tag and MKI) supported by libSRTP.  This value is
* the maximum number of octets that will be added to an RTCP packet by
* srtp_protect_rtcp().
*
* @brief the maximum number of octets added by srtp_protect().
*/
#define SRTP_MAX_SRTCP_TRAILER_LEN                                             \
   (SRTP_SRCTP_INDEX_LEN + SRTP_MAX_TAG_LEN + SRTP_MAX_MKI_LEN)

/**
* SRTP_MAX_NUM_MASTER_KEYS is the maximum number of Master keys for
* MKI supported by libSRTP.
*
*/
#define SRTP_MAX_NUM_MASTER_KEYS 16

#define SRTP_SALT_LEN 14

/*
* 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_KEY_LEN 16
#define SRTP_AES_192_KEY_LEN 24
#define SRTP_AES_256_KEY_LEN 32

#define SRTP_AES_ICM_128_KEY_LEN_WSALT (SRTP_SALT_LEN + SRTP_AES_128_KEY_LEN)
#define SRTP_AES_ICM_192_KEY_LEN_WSALT (SRTP_SALT_LEN + SRTP_AES_192_KEY_LEN)
#define SRTP_AES_ICM_256_KEY_LEN_WSALT (SRTP_SALT_LEN + SRTP_AES_256_KEY_LEN)

#define SRTP_AES_GCM_128_KEY_LEN_WSALT                                         \
   (SRTP_AEAD_SALT_LEN + SRTP_AES_128_KEY_LEN)
#define SRTP_AES_GCM_192_KEY_LEN_WSALT                                         \
   (SRTP_AEAD_SALT_LEN + SRTP_AES_192_KEY_LEN)
#define SRTP_AES_GCM_256_KEY_LEN_WSALT                                         \
   (SRTP_AEAD_SALT_LEN + SRTP_AES_256_KEY_LEN)

/**
*  @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 available; 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
*  available; 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_bad_mki = 25,       /**< error MKI present in packet is  */
                                       /**< invalid                         */
   srtp_err_status_pkt_idx_old = 26,   /**< packet index is too old to      */
                                       /**< consider                        */
   srtp_err_status_pkt_idx_adv = 27    /**< packet index advanced, reset    */
                                       /**< needed                          */
} srtp_err_status_t;

typedef struct srtp_ctx_t_ srtp_ctx_t;

/**
* @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 information.
*/
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 srtp_master_key_t represents a master key.  There will
* be a Master Key Index and the Master Key associated with the
* Master Key Index.  Need to also keep track of the Master Key
* Index Size to correctly read it from a packet.
*/
typedef struct srtp_master_key_t {
   unsigned char *key;
   unsigned char *mki_id;
   unsigned int mki_size;
} srtp_master_key_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_master_key_t **keys;      /** Array of Master Key structures       */
   unsigned long num_master_keys; /** Number of master keys                */
   void *deprecated_ekt;          /**< DEPRECATED: pointer to the EKT      */
                                  /**< policy structure for this stream    */
   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 intentionally 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 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_protect_mki() is the Secure RTP sender-side packet processing
* function that can utilize MKI.
*
* 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 pkt_octet_len 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.
*
* @param use_mki is a boolean to tell the system if mki is being used.  If
* set to false then will use the first set of session keys.  If set to true
* will
* use the session keys identified by the mki_index
*
* @param mki_index integer value specifying which set of session keys should be
* used if use_mki is set to true.
*
* @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_mki(srtp_ctx_t *ctx,
                                  void *rtp_hdr,
                                  int *pkt_octet_len,
                                  unsigned int use_mki,
                                  unsigned int mki_index);

/**
* @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_unprotect_mki() is the Secure RTP receiver-side packet
* processing function that checks for MKI.
*
* 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.
*
* @param use_mki is a boolean to tell the system if mki is being used.  If
* set to false then will use the first set of session keys.  If set to true
* will
* use the session keys identified by the mki_index
*
* @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).
*    - srtp_err_status_bad_mki if the MKI in the packet is not a known MKI id
*    - [other]  if there has been an error in the cryptographic mechanisms.
*
*/
srtp_err_status_t srtp_unprotect_mki(srtp_t ctx,
                                    void *srtp_hdr,
                                    int *len_ptr,
                                    unsigned int use_mki);

/**
* @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 succeeded.
*    - 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 succeeded.
*    - 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 succeeded.
*    - [other]           otherwise.
*
*/
srtp_err_status_t srtp_remove_stream(srtp_t session, uint32_t ssrc);

/**
* @brief srtp_update() updates 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 existing 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 succeed.
*    - 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() updates 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 existing 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 succeeded.
*    - 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 srtp_crypto_policy_set_rtp_default(&p) sets the
* srtp_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 srtp_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 forgo 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 forgo 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
* troubleshooting.
*
* 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 forgo 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 RFC 6188.  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 RFC 6188.  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_cm_192_hmac_sha1_80() sets a crypto
* policy structure to a encryption and authentication policy using AES-192
* for RTP protection.
*
* @param p is a pointer to the policy structure to be set
*
* The function call srtp_crypto_policy_set_aes_cm_192_hmac_sha1_80(&p)
* sets the srtp_crypto_policy_t at location p to use policy
* AES_CM_192_HMAC_SHA1_80 as defined in RFC 6188.  This policy uses AES-192
* 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_192_hmac_sha1_80(srtp_crypto_policy_t *p);

/**
* @brief srtp_crypto_policy_set_aes_cm_192_hmac_sha1_32() sets a crypto
* policy structure to a short-authentication tag policy using AES-192
* encryption.
*
* @param p is a pointer to the policy structure to be set
*
* The function call srtp_crypto_policy_set_aes_cm_192_hmac_sha1_32(&p)
* sets the srtp_crypto_policy_t at location p to use policy
* AES_CM_192_HMAC_SHA1_32 as defined in RFC 6188.  This policy uses AES-192
* 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_192_hmac_sha1_32(srtp_crypto_policy_t *p);

/**
* @brief srtp_crypto_policy_set_aes_cm_192_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_192_null_auth(&p) sets
* the srtp_crypto_policy_t at location p to use the SRTP default cipher
* (AES-192 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_192_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 occurred.
*/
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).
*/
typedef enum {
   srtp_profile_reserved = 0,
   srtp_profile_aes128_cm_sha1_80 = 1,
   srtp_profile_aes128_cm_sha1_32 = 2,
   srtp_profile_null_sha1_80 = 5,
   srtp_profile_null_sha1_32 = 6,
   srtp_profile_aead_aes_128_gcm = 7,
   srtp_profile_aead_aes_256_gcm = 8
} 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 policy is a pointer to the policy structure to be set
*
* @param profile is an enumeration for the policy 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 policy is a pointer to the policy structure to be set
*
* @param profile is an enumeration for the policy 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_SRTCP_TRAILER_LEN
* 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_protect_rtcp_mki() is the Secure RTCP sender-side packet
* processing function that can utilize mki.
*
* 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_SRTCP_TRAILER_LEN
* 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.
*
* @param use_mki is a boolean to tell the system if mki is being used.  If
* set to false then will use the first set of session keys.  If set to true
* will
* use the session keys identified by the mki_index
*
* @param mki_index integer value specifying which set of session keys should be
* used if use_mki is set to true.
*
* @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_mki(srtp_t ctx,
                                       void *rtcp_hdr,
                                       int *pkt_octet_len,
                                       unsigned int use_mki,
                                       unsigned int mki_index);

/**
* @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);

/**
* @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.
*
* @param use_mki is a boolean to tell the system if mki is being used.  If
* set to false then will use the first set of session keys.  If set to true
* will use the session keys identified by the mki_index
*
* @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).
*    - srtp_err_status_bad_mki     if the MKI in the packet is not a known MKI
*                                  id
*    - [other]                     if there has been an error in the
*                                  cryptographic mechanisms.
*
*/
srtp_err_status_t srtp_unprotect_rtcp_mki(srtp_t ctx,
                                         void *srtcp_hdr,
                                         int *pkt_octet_len,
                                         unsigned int use_mki);

/**
* @}
*/

/**
* @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 occurred.           */
   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 happened.       */
   uint32_t ssrc;      /**< The ssrc in host order of the stream in which  */
                       /**< the event happened                             */
   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 function 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(const 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);

/**
* @brief srtp_log_level_t defines log levels.
*
* The enumeration srtp_log_level_t defines log levels reported
* in the srtp_log_handler_func_t.
*
*/
typedef enum {
   srtp_log_level_error,   /**< log level is reporting an error message  */
   srtp_log_level_warning, /**< log level is reporting a warning message */
   srtp_log_level_info,    /**< log level is reporting an info message   */
   srtp_log_level_debug    /**< log level is reporting a debug message   */
} srtp_log_level_t;

/**
* @brief srtp_log_handler_func_t is the function prototype for
* the log handler.
*
* The typedef srtp_event_handler_func_t is the prototype for the
* event handler function.  It has as srtp_log_level_t, log
* message and data as arguments.
* There can only be a single, global handler for all log messages in
* libSRTP.
*/
typedef void(srtp_log_handler_func_t)(srtp_log_level_t level,
                                     const char *msg,
                                     void *data);

/**
* @brief sets the log handler to the function supplied by the caller.
*
* The function call srtp_install_log_handler(func) sets the log
* handler function to the value func.  The value NULL is acceptable
* as an argument; in this case, log messages will be ignored.
* This function can be called before srtp_init() in order to capture
* any logging during start up.
*
* @param func is a pointer to a function of type srtp_log_handler_func_t.
*             This function will be used by libSRTP to output log messages.
* @param data is a user pointer that will be returned as the data argument in
* func.
*/
srtp_err_status_t srtp_install_log_handler(srtp_log_handler_func_t func,
                                          void *data);

/**
* @brief srtp_get_protect_trailer_length(session, use_mki, mki_index, length)
*
* Determines the length of the amount of data Lib SRTP will add to the
* packet during the protect process. The length is returned in the length
* parameter
*
* returns err_status_ok on success, err_status_bad_mki if the MKI index is
* invalid
*
*/
srtp_err_status_t srtp_get_protect_trailer_length(srtp_t session,
                                                 uint32_t use_mki,
                                                 uint32_t mki_index,
                                                 uint32_t *length);

/**
* @brief srtp_get_protect_rtcp_trailer_length(session, use_mki, mki_index,
* length)
*
* Determines the length of the amount of data Lib SRTP will add to the
* packet during the protect process. The length is returned in the length
* parameter
*
* returns err_status_ok on success, err_status_bad_mki if the MKI index is
* invalid
*
*/
srtp_err_status_t srtp_get_protect_rtcp_trailer_length(srtp_t session,
                                                      uint32_t use_mki,
                                                      uint32_t mki_index,
                                                      uint32_t *length);

/**
* @brief srtp_set_stream_roc(session, ssrc, roc)
*
* Set the roll-over-counter on a session for a given SSRC
*
* returns err_status_ok on success, srtp_err_status_bad_param if there is no
* stream found
*
*/
srtp_err_status_t srtp_set_stream_roc(srtp_t session,
                                     uint32_t ssrc,
                                     uint32_t roc);

/**
* @brief srtp_get_stream_roc(session, ssrc, roc)
*
* Get the roll-over-counter on a session for a given SSRC
*
* returns err_status_ok on success, srtp_err_status_bad_param if there is no
* stream found
*
*/
srtp_err_status_t srtp_get_stream_roc(srtp_t session,
                                     uint32_t ssrc,
                                     uint32_t *roc);

/**
* @}
*/

/* 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_SRTP_H */