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 /*

  * 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

 #ifdef __cplusplus

 extern "C" {

 #endif

 #include "srtp_priv.h"

 #define EKT_CIPHER_DEFAULT           1

 #define EKT_CIPHER_AES_128_ECB       1

 #define EKT_CIPHER_AES_192_KEY_WRAP  2

 #define EKT_CIPHER_AES_256_KEY_WRAP  3

 typedef uint16_t ekt_spi_t;

 unsigned

 ekt_octets_after_base_tag(ekt_stream_t ekt);

 /*

  * an srtp_policy_t structure can contain a pointer to an

  * 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 ekt_policy_ctx_t {

   ekt_spi_t  spi;     /* security parameter index */

   uint8_t    ekt_cipher_type;

   uint8_t   *ekt_key;

   struct ekt_policy_ctx_t *next_ekt_policy;

 } ekt_policy_ctx_t;

 /*

  * an ekt_data_t structure holds the data corresponding to an ekt key,

  * spi, and so on

  */

 typedef struct ekt_data_t {

   ekt_spi_t spi;

   uint8_t ekt_cipher_type;

   aes_expanded_key_t ekt_enc_key;

   aes_expanded_key_t ekt_dec_key;

   struct ekt_data_t *next_ekt_data;

 } ekt_data_t;

 /*

  * an srtp_stream_ctx_t can contain an ekt_stream_ctx_t

  *

  * an ekt_stream_ctx_t structure holds all of the EKT information for

  * a specific SRTP stream

  */

 typedef struct ekt_stream_ctx_t {

   ekt_data_t *data;    

   uint16_t    isn;     /* initial sequence number  */

   uint8_t     encrypted_master_key[SRTP_MAX_KEY_LEN];

 } ekt_stream_ctx_t;

 err_status_t 

 ekt_alloc(ekt_stream_t *stream_data, ekt_policy_t policy);

 err_status_t

 ekt_stream_init(ekt_stream_t e, 

 		ekt_spi_t spi,

 		void *ekt_key,

 		unsigned ekt_cipher_type);

 err_status_t

 ekt_stream_init_from_policy(ekt_stream_t e, ekt_policy_t p);

 err_status_t

 srtp_stream_init_from_ekt(srtp_stream_t stream,			  

 			  const void *srtcp_hdr,

 			  unsigned pkt_octet_len);

 void

 ekt_write_data(ekt_stream_t ekt,

 	       uint8_t *base_tag, 

 	       unsigned base_tag_len, 

 	       int *packet_len,

 	       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

  */

 err_status_t

 ekt_tag_verification_preproces(uint8_t *pkt_tag, 

 			       uint8_t *pkt_tag_copy, 

 			       unsigned tag_len);

 err_status_t

 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.

  * 

  */

 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 */

 err_status_t

 srtcp_auth_tag_generation_postprocess(void);

 #ifdef __cplusplus

 }

 #endif

 #endif /* EKT_H */