aes_icm.c

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/*
 * aes_icm.c
 *
 * AES Integer Counter Mode
 *
 * David A. McGrew
 * Cisco Systems, Inc.
 */

/*
 *	
 * Copyright (c) 2001-2005, Cisco Systems, Inc.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 *   Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * 
 *   Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 * 
 *   Neither the name of the Cisco Systems, Inc. nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */


#define ALIGN_32 0

#include "aes_icm.h"
#include "alloc.h"


debug_module_t mod_aes_icm = {
  0,                 /* debugging is off by default */
  "aes icm"          /* printable module name       */
};

/*
 * integer counter mode works as follows:
 *
 * 16 bits
 * <----->
 * +------+------+------+------+------+------+------+------+ 
 * |           nonce           |    pakcet index    |  ctr |---+
 * +------+------+------+------+------+------+------+------+   |
 *                                                             |
 * +------+------+------+------+------+------+------+------+   v
 * |                      salt                      |000000|->(+)
 * +------+------+------+------+------+------+------+------+   |
 *                                                             |
 *                                                        +---------+
 *							  | encrypt |
 *							  +---------+
 *							       | 
 * +------+------+------+------+------+------+------+------+   |
 * |                    keystream block                    |<--+ 
 * +------+------+------+------+------+------+------+------+   
 *
 * All fields are big-endian
 *
 * ctr is the block counter, which increments from zero for
 * each packet (16 bits wide)
 * 
 * packet index is distinct for each packet (48 bits wide)
 *
 * nonce can be distinct across many uses of the same key, or
 * can be a fixed value per key, or can be per-packet randomness
 * (64 bits)
 *
 */

err_status_t
aes_icm_alloc_ismacryp(cipher_t **c, int key_len, int forIsmacryp) {
  extern cipher_type_t aes_icm;
  uint8_t *pointer;
  int tmp;

  debug_print(mod_aes_icm, 
            "allocating cipher with key length %d", key_len);

  // Ismacryp, for example, uses 16 byte key + 8 byte 
  // salt  so this function is called with key_len = 24.
  // The check for key_len = 30 does not apply. Our usage
  // of aes functions with key_len = values other than 30
  // has not broken anything. Don't know what would be the
  // effect of skipping this check for srtp in general.
  if (!forIsmacryp && key_len != 30)
    return err_status_bad_param;

  /* allocate memory a cipher of type aes_icm */
  tmp = (sizeof(aes_icm_ctx_t) + sizeof(cipher_t));
  pointer = crypto_alloc(tmp);
  if (pointer == NULL) 
    return err_status_alloc_fail;

  /* set pointers */
  *c = (cipher_t *)pointer;
  (*c)->type = &aes_icm;
  (*c)->state = pointer + sizeof(cipher_t);

  /* increment ref_count */
  aes_icm.ref_count++;

  /* set key size        */
  (*c)->key_len = key_len;

  return err_status_ok;  
}

err_status_t aes_icm_alloc(cipher_t **c, int key_len, int forIsmacryp) {
  return aes_icm_alloc_ismacryp(c, key_len, 0);
}

err_status_t
aes_icm_dealloc(cipher_t *c) {
  extern cipher_type_t aes_icm;

  /* zeroize entire state*/
  octet_string_set_to_zero((uint8_t *)c, 
			   sizeof(aes_icm_ctx_t) + sizeof(cipher_t));

  /* free memory */
  crypto_free(c);

  /* decrement ref_count */
  aes_icm.ref_count--;
  
  return err_status_ok;  
}


/*
 * aes_icm_context_init(...) initializes the aes_icm_context
 * using the value in key[].
 *
 * the key is the secret key 
 *
 * the salt is unpredictable (but not necessarily secret) data which
 * randomizes the starting point in the keystream
 */

err_status_t
aes_icm_context_init(aes_icm_ctx_t *c, const uint8_t *key) {
  v128_t tmp_key;

  /* set counter and initial values to 'offset' value */
  /* FIX!!! this assumes the salt is at key + 16, and thus that the */
  /* FIX!!! cipher key length is 16!  Also note this copies past the
            end of the 'key' array by 2 bytes! */
  v128_copy_octet_string(&c->counter, key + 16);
  v128_copy_octet_string(&c->offset, key + 16);

  /* force last two octets of the offset to zero (for srtp compatibility) */
  c->offset.v8[14] = c->offset.v8[15] = 0;
  c->counter.v8[14] = c->counter.v8[15] = 0;
  
  /* set tmp_key (for alignment) */
  v128_copy_octet_string(&tmp_key, key);

  debug_print(mod_aes_icm, 
	      "key:  %s", v128_hex_string(&tmp_key)); 
  debug_print(mod_aes_icm, 
	      "offset: %s", v128_hex_string(&c->offset)); 

  /* expand key */
  aes_expand_encryption_key(&tmp_key, c->expanded_key);

  /* indicate that the keystream_buffer is empty */
  c->bytes_in_buffer = 0;

  return err_status_ok;
}

/*
 * aes_icm_set_octet(c, i) sets the counter of the context which it is
 * passed so that the next octet of keystream that will be generated
 * is the ith octet
 */

err_status_t
aes_icm_set_octet(aes_icm_ctx_t *c,
		  uint64_t octet_num) {

#ifdef NO_64BIT_MATH
  int tail_num       = low32(octet_num) & 0x0f;
  /* 64-bit right-shift 4 */
  uint64_t block_num = make64(high32(octet_num) >> 4,
							  ((high32(octet_num) & 0x0f)<<(32-4)) |
							   (low32(octet_num) >> 4));
#else
  int tail_num       = octet_num % 16;
  uint64_t block_num = octet_num / 16;
#endif
  

  /* set counter value */
  /* FIX - There's no way this is correct */
  c->counter.v64[0] = c->offset.v64[0];
#ifdef NO_64BIT_MATH
  c->counter.v64[0] = make64(high32(c->offset.v64[0]) ^ high32(block_num),
							 low32(c->offset.v64[0])  ^ low32(block_num));
#else
  c->counter.v64[0] = c->offset.v64[0] ^ block_num;
#endif

  debug_print(mod_aes_icm, 
	      "set_octet: %s", v128_hex_string(&c->counter)); 

  /* fill keystream buffer, if needed */
  if (tail_num) {
    v128_copy(&c->keystream_buffer, &c->counter);
    aes_encrypt(&c->keystream_buffer, c->expanded_key);
    c->bytes_in_buffer = sizeof(v128_t);

    debug_print(mod_aes_icm, "counter:    %s", 
	      v128_hex_string(&c->counter));
    debug_print(mod_aes_icm, "ciphertext: %s", 
	      v128_hex_string(&c->keystream_buffer));    
    
    /*  indicate number of bytes in keystream_buffer  */
    c->bytes_in_buffer = sizeof(v128_t) - tail_num;
  
  } else {
    
    /* indicate that keystream_buffer is empty */
    c->bytes_in_buffer = 0;
  }

  return err_status_ok;
}

/*
 * aes_icm_set_iv(c, iv) sets the counter value to the exor of iv with
 * the offset
 */