text: /*
   * ekt.h
   *
   * interface to Encrypted Key Transport for SRTP
   *
   * David McGrew
   * Cisco Systems, Inc.
   */
  /*
   *	
   * Copyright (c) 2001-2005 Cisco Systems, Inc.
   * All rights reserved.
   * 
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 
   *   Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   * 
   *   Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   * 
   *   Neither the name of the Cisco Systems, Inc. nor the names of its
   *   contributors may be used to endorse or promote products derived
   *   from this software without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   */
  
  
  
  /*
   * EKT implementation strategy 
   * 
   * use stream_template approach
   *
   * in srtp_unprotect, when a new stream appears, check if template has
   * EKT defined, and if it does, then apply EKT processing 
   *
   * question: will we want to allow key-sharing templates in addition
   * to EKT templates?  could define a new ssrc_type_t that's associated
   * with an EKT, e.g.  ssrc_any_ekt.
   *
   *
   */
  
  #ifndef EKT_H
  #define EKT_H
  
  #include "srtp_priv.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #define SRTP_EKT_CIPHER_DEFAULT           1
  #define SRTP_EKT_CIPHER_AES_128_ECB       1
  #define SRTP_EKT_CIPHER_AES_192_KEY_WRAP  2
  #define SRTP_EKT_CIPHER_AES_256_KEY_WRAP  3
  
  typedef uint16_t srtp_ekt_spi_t;
  
  
  unsigned srtp_ekt_octets_after_base_tag(srtp_ekt_stream_t ekt);
  
  /*
   * an srtp_policy_t structure can contain a pointer to an
   * srtp_ekt_policy_t structure
   *
   * this structure holds all of the high level EKT information, and it
   * is passed into libsrtp to indicate what policy should be in effect
   */
  
  typedef struct srtp_ekt_policy_ctx_t {
    srtp_ekt_spi_t  spi;     /* security parameter index */
    uint8_t    ekt_cipher_type;
    uint8_t   *ekt_key;
    struct srtp_ekt_policy_ctx_t *next_ekt_policy;
  } srtp_ekt_policy_ctx_t;
  
  
  /*
   * an srtp_ekt_data_t structure holds the data corresponding to an ekt key,
   * spi, and so on
   */
  
  typedef struct srtp_ekt_data_t {
    srtp_ekt_spi_t spi;
    uint8_t ekt_cipher_type;
    srtp_aes_expanded_key_t ekt_enc_key;
    srtp_aes_expanded_key_t ekt_dec_key;
    struct ekt_data_t *next_ekt_data;
  } srtp_ekt_data_t;
  
  /*
   * an srtp_stream_ctx_t can contain an srtp_ekt_stream_ctx_t
   *
   * an srtp_ekt_stream_ctx_t structure holds all of the EKT information for
   * a specific SRTP stream
   */
  
  typedef struct srtp_ekt_stream_ctx_t {
    srtp_ekt_data_t   *data;    
    uint16_t	    isn;     /* initial sequence number  */
    uint8_t	    encrypted_master_key[SRTP_MAX_KEY_LEN];
  } srtp_ekt_stream_ctx_t;
  
  
  
  srtp_err_status_t srtp_ekt_alloc(srtp_ekt_stream_t *stream_data, srtp_ekt_policy_t policy);
  
  srtp_err_status_t srtp_ekt_stream_init(srtp_ekt_stream_t e, srtp_ekt_spi_t spi, void *ekt_key, unsigned ekt_cipher_type);
  
  srtp_err_status_t srtp_ekt_stream_init_from_policy(srtp_ekt_stream_t e, srtp_ekt_policy_t p);
    
  
  
  srtp_err_status_t srtp_stream_init_from_ekt(srtp_stream_t stream, const void *srtcp_hdr, unsigned pkt_octet_len);
  		
  
  void srtp_ekt_write_data(srtp_ekt_stream_t ekt, uint8_t *base_tag, unsigned base_tag_len, int *packet_len, srtp_xtd_seq_num_t pkt_index);		
  
  /*
   * We handle EKT by performing some additional steps before
   * authentication (copying the auth tag into a temporary location,
   * zeroizing the "base tag" field in the packet)
   *
   * With EKT, the tag_len parameter is actually the base tag
   * length
   */
  srtp_err_status_t srtp_ekt_tag_verification_preproces(uint8_t *pkt_tag, uint8_t *pkt_tag_copy, unsigned tag_len);
  
  srtp_err_status_t srtp_ekt_tag_verification_postproces(uint8_t *pkt_tag, uint8_t *pkt_tag_copy, unsigned tag_len);
  
  
  /*
   * @brief EKT pre-processing for srtcp tag generation
   *
   * This function does the pre-processing of the SRTCP authentication
   * tag format.  When EKT is used, it consists of writing the Encrypted
   * Master Key, the SRTP ROC, the Initial Sequence Number, and SPI
   * fields.  The Base Authentication Tag field is set to the all-zero
   * value
   * 
   * When EKT is not used, this function is a no-op.
   * 
   */
  srtp_err_status_t srtp_stream_srtcp_auth_tag_generation_preprocess(const srtp_stream_t *s, uint8_t *pkt_tag, unsigned pkt_octet_len);
  
  /* it's not clear that a tag_generation_postprocess function is needed */
  srtp_err_status_t srtcp_auth_tag_generation_postprocess(void);
  
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* EKT_H */
  