/*
* aes_icm.c
*
* AES Integer Counter Mode
*
* 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.
*
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#define ALIGN_32 0
#include "aes_icm.h"
#include "alloc.h"
#include "cipher_types.h"
#include "cipher_test_cases.h"
srtp_debug_module_t srtp_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)
*
*/
static srtp_err_status_t srtp_aes_icm_alloc(srtp_cipher_t **c,
int key_len,
int tlen)
{
srtp_aes_icm_ctx_t *icm;
(void)tlen;
debug_print(srtp_mod_aes_icm, "allocating cipher with key length %d",
key_len);
/*
* The check for key_len = 30/46 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 (key_len != SRTP_AES_ICM_128_KEY_LEN_WSALT &&
key_len != SRTP_AES_ICM_256_KEY_LEN_WSALT) {
return srtp_err_status_bad_param;
}
/* allocate memory a cipher of type aes_icm */
*c = (srtp_cipher_t *)srtp_crypto_alloc(sizeof(srtp_cipher_t));
if (*c == NULL) {
return srtp_err_status_alloc_fail;
}
icm = (srtp_aes_icm_ctx_t *)srtp_crypto_alloc(sizeof(srtp_aes_icm_ctx_t));
if (icm == NULL) {
srtp_crypto_free(*c);
*c = NULL;
return srtp_err_status_alloc_fail;
}
/* set pointers */
(*c)->state = icm;
switch (key_len) {
case SRTP_AES_ICM_256_KEY_LEN_WSALT:
(*c)->algorithm = SRTP_AES_ICM_256;
(*c)->type = &srtp_aes_icm_256;
break;
default:
(*c)->algorithm = SRTP_AES_ICM_128;
(*c)->type = &srtp_aes_icm_128;
break;
}
/* set key size */
icm->key_size = key_len;
(*c)->key_len = key_len;
return srtp_err_status_ok;
}
static srtp_err_status_t srtp_aes_icm_dealloc(srtp_cipher_t *c)
{
srtp_aes_icm_ctx_t *ctx;
if (c == NULL) {
return srtp_err_status_bad_param;
}
ctx = (srtp_aes_icm_ctx_t *)c->state;
if (ctx) {
/* zeroize the key material */
octet_string_set_to_zero(ctx, sizeof(srtp_aes_icm_ctx_t));
srtp_crypto_free(ctx);
}
/* free the cipher context */
srtp_crypto_free(c);
return srtp_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
*/
static srtp_err_status_t srtp_aes_icm_context_init(void *cv, const uint8_t *key)
{
srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
srtp_err_status_t status;
int base_key_len, copy_len;
if (c->key_size == SRTP_AES_ICM_128_KEY_LEN_WSALT ||
c->key_size == SRTP_AES_ICM_256_KEY_LEN_WSALT) {
base_key_len = c->key_size - SRTP_SALT_LEN;
} else {
return srtp_err_status_bad_param;
}
/*
* set counter and initial values to 'offset' value, being careful not to
* go past the end of the key buffer
*/
v128_set_to_zero(&c->counter);
v128_set_to_zero(&c->offset);
copy_len = c->key_size - base_key_len;
/* force last two octets of the offset to be left zero (for srtp
* compatibility) */
if (copy_len > SRTP_SALT_LEN) {
copy_len = SRTP_SALT_LEN;
}
memcpy(&c->counter, key + base_key_len, copy_len);
memcpy(&c->offset, key + base_key_len, copy_len);
debug_print(srtp_mod_aes_icm, "key: %s",
srtp_octet_string_hex_string(key, base_key_len));
debug_print(srtp_mod_aes_icm, "offset: %s", v128_hex_string(&c->offset));
/* expand key */
status =
srtp_aes_expand_encryption_key(key, base_key_len, &c->expanded_key);
if (status) {
v128_set_to_zero(&c->counter);
v128_set_to_zero(&c->offset);
return status;
}
/* indicate that the keystream_buffer is empty */
c->bytes_in_buffer = 0;
return srtp_err_status_ok;
}
/*
* aes_icm_set_iv(c, iv) sets the counter value to the exor of iv with
* the offset
*/
static srtp_err_status_t srtp_aes_icm_set_iv(void *cv,
uint8_t *iv,
srtp_cipher_direction_t direction)
{
srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
v128_t nonce;
(void)direction;
/* set nonce (for alignment) */
v128_copy_octet_string(&nonce, iv);
debug_print(srtp_mod_aes_icm, "setting iv: %s", v128_hex_string(&nonce));
v128_xor(&c->counter, &c->offset, &nonce);
debug_print(srtp_mod_aes_icm, "set_counter: %s",
v128_hex_string(&c->counter));
/* indicate that the keystream_buffer is empty */
c->bytes_in_buffer = 0;
return srtp_err_status_ok;
}
/*
* aes_icm_advance(...) refills the keystream_buffer and
* advances the block index of the sicm_context forward by one
*
* this is an internal, hopefully inlined function
*/
static void srtp_aes_icm_advance(srtp_aes_icm_ctx_t *c)
{
/* fill buffer with new keystream */
v128_copy(&c->keystream_buffer, &c->counter);
srtp_aes_encrypt(&c->keystream_buffer, &c->expanded_key);
c->bytes_in_buffer = sizeof(v128_t);
debug_print(srtp_mod_aes_icm, "counter: %s",
v128_hex_string(&c->counter));
debug_print(srtp_mod_aes_icm, "ciphertext: %s",
v128_hex_string(&c->keystream_buffer));
/* clock counter forward */
if (!++(c->counter.v8[15])) {
++(c->counter.v8[14]);
}
}
/*
* icm_encrypt deals with the following cases:
*
* bytes_to_encr < bytes_in_buffer
* - add keystream into data
*
* bytes_to_encr > bytes_in_buffer
* - add keystream into data until keystream_buffer is depleted
* - loop over blocks, filling keystream_buffer and then
* adding keystream into data
* - fill buffer then add in remaining (< 16) bytes of keystream
*/
static srtp_err_status_t srtp_aes_icm_encrypt(void *cv,
unsigned char *buf,
unsigned int *enc_len)
{
srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
unsigned int bytes_to_encr = *enc_len;
unsigned int i;
uint32_t *b;
/* check that there's enough segment left*/
unsigned int bytes_of_new_keystream = bytes_to_encr - c->bytes_in_buffer;
unsigned int blocks_of_new_keystream = (bytes_of_new_keystream + 15) >> 4;
if ((blocks_of_new_keystream + htons(c->counter.v16[7])) > 0xffff) {
return srtp_err_status_terminus;
}
debug_print(srtp_mod_aes_icm, "block index: %d", htons(c->counter.v16[7]));
if (bytes_to_encr <= (unsigned int)c->bytes_in_buffer) {
/* deal with odd case of small bytes_to_encr */
for (i = (sizeof(v128_t) - c->bytes_in_buffer);
i < (sizeof(v128_t) - c->bytes_in_buffer + bytes_to_encr); i++) {
*buf++ ^= c->keystream_buffer.v8[i];
}
c->bytes_in_buffer -= bytes_to_encr;
/* return now to avoid the main loop */
return srtp_err_status_ok;
} else {
/* encrypt bytes until the remaining data is 16-byte aligned */
for (i = (sizeof(v128_t) - c->bytes_in_buffer); i < sizeof(v128_t);
i++) {
*buf++ ^= c->keystream_buffer.v8[i];
}
bytes_to_encr -= c->bytes_in_buffer;
c->bytes_in_buffer = 0;
}
/* now loop over entire 16-byte blocks of keystream */
for (i = 0; i < (bytes_to_encr / sizeof(v128_t)); i++) {
/* fill buffer with new keystream */
srtp_aes_icm_advance(c);
/*
* add keystream into the data buffer (this would be a lot faster
* if we could assume 32-bit alignment!)
*/
#if ALIGN_32
b = (uint32_t *)buf;
*b++ ^= c->keystream_buffer.v32[0];
*b++ ^= c->keystream_buffer.v32[1];
*b++ ^= c->keystream_buffer.v32[2];
*b++ ^= c->keystream_buffer.v32[3];
buf = (uint8_t *)b;
#else
if ((((uintptr_t)buf) & 0x03) != 0) {
*buf++ ^= c->keystream_buffer.v8[0];
*buf++ ^= c->keystream_buffer.v8[1];
*buf++ ^= c->keystream_buffer.v8[2];
*buf++ ^= c->keystream_buffer.v8[3];
*buf++ ^= c->keystream_buffer.v8[4];
*buf++ ^= c->keystream_buffer.v8[5];
*buf++ ^= c->keystream_buffer.v8[6];
*buf++ ^= c->keystream_buffer.v8[7];
*buf++ ^= c->keystream_buffer.v8[8];
*buf++ ^= c->keystream_buffer.v8[9];
*buf++ ^= c->keystream_buffer.v8[10];
*buf++ ^= c->keystream_buffer.v8[11];
*buf++ ^= c->keystream_buffer.v8[12];
*buf++ ^= c->keystream_buffer.v8[13];
*buf++ ^= c->keystream_buffer.v8[14];
*buf++ ^= c->keystream_buffer.v8[15];
} else {
b = (uint32_t *)buf;
*b++ ^= c->keystream_buffer.v32[0];
*b++ ^= c->keystream_buffer.v32[1];
*b++ ^= c->keystream_buffer.v32[2];
*b++ ^= c->keystream_buffer.v32[3];
buf = (uint8_t *)b;
}
#endif /* #if ALIGN_32 */
}
/* if there is a tail end of the data, process it */
if ((bytes_to_encr & 0xf) != 0) {
/* fill buffer with new keystream */
srtp_aes_icm_advance(c);
for (i = 0; i < (bytes_to_encr & 0xf); i++) {
*buf++ ^= c->keystream_buffer.v8[i];
}
/* reset the keystream buffer size to right value */
c->bytes_in_buffer = sizeof(v128_t) - i;
} else {
/* no tail, so just reset the keystream buffer size to zero */
c->bytes_in_buffer = 0;
}
return srtp_err_status_ok;
}
static const char srtp_aes_icm_128_description[] =
"AES-128 integer counter mode";
static const char srtp_aes_icm_256_description[] =
"AES-256 integer counter mode";
/*
* note: the encrypt function is identical to the decrypt function
*/
const srtp_cipher_type_t srtp_aes_icm_128 = {
srtp_aes_icm_alloc, /* */
srtp_aes_icm_dealloc, /* */
srtp_aes_icm_context_init, /* */
0, /* set_aad */
srtp_aes_icm_encrypt, /* */
srtp_aes_icm_encrypt, /* */
srtp_aes_icm_set_iv, /* */
0, /* get_tag */
srtp_aes_icm_128_description, /* */
&srtp_aes_icm_128_test_case_0, /* */
SRTP_AES_ICM_128 /* */
};
const srtp_cipher_type_t srtp_aes_icm_256 = {
srtp_aes_icm_alloc, /* */
srtp_aes_icm_dealloc, /* */
srtp_aes_icm_context_init, /* */
0, /* set_aad */
srtp_aes_icm_encrypt, /* */
srtp_aes_icm_encrypt, /* */
srtp_aes_icm_set_iv, /* */
0, /* get_tag */
srtp_aes_icm_256_description, /* */
&srtp_aes_icm_256_test_case_0, /* */
SRTP_AES_ICM_256 /* */
};