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/* ctr_prng.c - TinyCrypt implementation of CTR-PRNG */
/*
* Copyright (c) 2016, Chris Morrison
* 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.
*
* 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 HOLDER 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.
*/
#include <tinycrypt/ctr_prng.h>
#include <tinycrypt/utils.h>
#include <tinycrypt/constants.h>
#include <string.h>
/*
* This PRNG is based on the CTR_DRBG described in Recommendation for Random
* Number Generation Using Deterministic Random Bit Generators,
* NIST SP 800-90A Rev. 1.
*
* Annotations to particular steps (e.g. 10.2.1.2 Step 1) refer to the steps
* described in that document.
*
*/
/**
* @brief Array incrementer
* Treats the supplied array as one contiguous number (MSB in arr[0]), and
* increments it by one
* @return none
* @param arr IN/OUT -- array to be incremented
* @param len IN -- size of arr in bytes
*/
static void arrInc(uint8_t arr[], unsigned int len)
{
unsigned int i;
if (0 != arr) {
for (i = len; i > 0U; i--) {
if (++arr[i-1] != 0U) {
break;
}
}
}
}
/**
* @brief CTR PRNG update
* Updates the internal state of supplied the CTR PRNG context
* increments it by one
* @return none
* @note Assumes: providedData is (TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE) bytes long
* @param ctx IN/OUT -- CTR PRNG state
* @param providedData IN -- data used when updating the internal state
*/
static void tc_ctr_prng_update(TCCtrPrng_t * const ctx, uint8_t const * const providedData)
{
if (0 != ctx) {
/* 10.2.1.2 step 1 */
uint8_t temp[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE];
unsigned int len = 0U;
/* 10.2.1.2 step 2 */
while (len < sizeof temp) {
unsigned int blocklen = sizeof(temp) - len;
uint8_t output_block[TC_AES_BLOCK_SIZE];
/* 10.2.1.2 step 2.1 */
arrInc(ctx->V, sizeof ctx->V);
/* 10.2.1.2 step 2.2 */
if (blocklen > TC_AES_BLOCK_SIZE) {
blocklen = TC_AES_BLOCK_SIZE;
}
(void)tc_aes_encrypt(output_block, ctx->V, &ctx->key);
/* 10.2.1.2 step 2.3/step 3 */
memcpy(&(temp[len]), output_block, blocklen);
len += blocklen;
}
/* 10.2.1.2 step 4 */
if (0 != providedData) {
unsigned int i;
for (i = 0U; i < sizeof temp; i++) {
temp[i] ^= providedData[i];
}
}
/* 10.2.1.2 step 5 */
(void)tc_aes128_set_encrypt_key(&ctx->key, temp);
/* 10.2.1.2 step 6 */
memcpy(ctx->V, &(temp[TC_AES_KEY_SIZE]), TC_AES_BLOCK_SIZE);
}
}
int tc_ctr_prng_init(TCCtrPrng_t * const ctx,
uint8_t const * const entropy,
unsigned int entropyLen,
uint8_t const * const personalization,
unsigned int pLen)
{
int result = TC_CRYPTO_FAIL;
unsigned int i;
uint8_t personalization_buf[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE] = {0U};
uint8_t seed_material[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE];
uint8_t zeroArr[TC_AES_BLOCK_SIZE] = {0U};
if (0 != personalization) {
/* 10.2.1.3.1 step 1 */
unsigned int len = pLen;
if (len > sizeof personalization_buf) {
len = sizeof personalization_buf;
}
/* 10.2.1.3.1 step 2 */
memcpy(personalization_buf, personalization, len);
}
if ((0 != ctx) && (0 != entropy) && (entropyLen >= sizeof seed_material)) {
/* 10.2.1.3.1 step 3 */
memcpy(seed_material, entropy, sizeof seed_material);
for (i = 0U; i < sizeof seed_material; i++) {
seed_material[i] ^= personalization_buf[i];
}
/* 10.2.1.3.1 step 4 */
(void)tc_aes128_set_encrypt_key(&ctx->key, zeroArr);
/* 10.2.1.3.1 step 5 */
memset(ctx->V, 0x00, sizeof ctx->V);
/* 10.2.1.3.1 step 6 */
tc_ctr_prng_update(ctx, seed_material);
/* 10.2.1.3.1 step 7 */
ctx->reseedCount = 1U;
result = TC_CRYPTO_SUCCESS;
}
return result;
}
int tc_ctr_prng_reseed(TCCtrPrng_t * const ctx,
uint8_t const * const entropy,
unsigned int entropyLen,
uint8_t const * const additional_input,
unsigned int additionallen)
{
unsigned int i;
int result = TC_CRYPTO_FAIL;
uint8_t additional_input_buf[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE] = {0U};
uint8_t seed_material[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE];
if (0 != additional_input) {
/* 10.2.1.4.1 step 1 */
unsigned int len = additionallen;
if (len > sizeof additional_input_buf) {
len = sizeof additional_input_buf;
}
/* 10.2.1.4.1 step 2 */
memcpy(additional_input_buf, additional_input, len);
}
unsigned int seedlen = (unsigned int)TC_AES_KEY_SIZE + (unsigned int)TC_AES_BLOCK_SIZE;
if ((0 != ctx) && (entropyLen >= seedlen)) {
/* 10.2.1.4.1 step 3 */
memcpy(seed_material, entropy, sizeof seed_material);
for (i = 0U; i < sizeof seed_material; i++) {
seed_material[i] ^= additional_input_buf[i];
}
/* 10.2.1.4.1 step 4 */
tc_ctr_prng_update(ctx, seed_material);
/* 10.2.1.4.1 step 5 */
ctx->reseedCount = 1U;
result = TC_CRYPTO_SUCCESS;
}
return result;
}
int tc_ctr_prng_generate(TCCtrPrng_t * const ctx,
uint8_t const * const additional_input,
unsigned int additionallen,
uint8_t * const out,
unsigned int outlen)
{
/* 2^48 - see section 10.2.1 */
static const uint64_t MAX_REQS_BEFORE_RESEED = 0x1000000000000ULL;
/* 2^19 bits - see section 10.2.1 */
static const unsigned int MAX_BYTES_PER_REQ = 65536U;
unsigned int result = TC_CRYPTO_FAIL;
if ((0 != ctx) && (0 != out) && (outlen < MAX_BYTES_PER_REQ)) {
/* 10.2.1.5.1 step 1 */
if (ctx->reseedCount > MAX_REQS_BEFORE_RESEED) {
result = TC_CTR_PRNG_RESEED_REQ;
} else {
uint8_t additional_input_buf[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE] = {0U};
if (0 != additional_input) {
/* 10.2.1.5.1 step 2 */
unsigned int len = additionallen;
if (len > sizeof additional_input_buf) {
len = sizeof additional_input_buf;
}
memcpy(additional_input_buf, additional_input, len);
tc_ctr_prng_update(ctx, additional_input_buf);
}
/* 10.2.1.5.1 step 3 - implicit */
/* 10.2.1.5.1 step 4 */
unsigned int len = 0U;
while (len < outlen) {
unsigned int blocklen = outlen - len;
uint8_t output_block[TC_AES_BLOCK_SIZE];
/* 10.2.1.5.1 step 4.1 */
arrInc(ctx->V, sizeof ctx->V);
/* 10.2.1.5.1 step 4.2 */
(void)tc_aes_encrypt(output_block, ctx->V, &ctx->key);
/* 10.2.1.5.1 step 4.3/step 5 */
if (blocklen > TC_AES_BLOCK_SIZE) {
blocklen = TC_AES_BLOCK_SIZE;
}
memcpy(&(out[len]), output_block, blocklen);
len += blocklen;
}
/* 10.2.1.5.1 step 6 */
tc_ctr_prng_update(ctx, additional_input_buf);
/* 10.2.1.5.1 step 7 */
ctx->reseedCount++;
/* 10.2.1.5.1 step 8 */
result = TC_CRYPTO_SUCCESS;
}
}
return result;
}
void tc_ctr_prng_uninstantiate(TCCtrPrng_t * const ctx)
{
if (0 != ctx) {
memset(ctx->key.words, 0x00, sizeof ctx->key.words);
memset(ctx->V, 0x00, sizeof ctx->V);
ctx->reseedCount = 0U;
}
}
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