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/* ctr_prng.c - TinyCrypt implementation of CTR-PRNG */
#include <tinycrypt/ctr_prng.h>
#include <tinycrypt/utils.h>
#include <string.h>
//todo comment
static void arrInc(uint8_t arr[], uint32_t len)
{
uint32_t i;
if (0 != arr)
{
for (i = len; i > 0U; i--)
{
if (++arr[i-1] != 0U)
{
break;
}
}
}
}
//todo comment
static void tc_ctr_prng_update(TCCtrPrng_t * const ctx, uint8_t const providedData[])
{
if (0 != ctx)
{
/* 10.2.1.2 step 1 */
uint8_t temp[TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE];
uint32_t len = 0U;
/* 10.2.1.2 step 2 */
while (len < sizeof temp)
{
uint32_t 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)
{
uint32_t 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);
}
}
int32_t tc_ctr_prng_init(TCCtrPrng_t * const ctx,
uint8_t const entropy[],
uint32_t entropyLen,
uint8_t const personalization[],
uint32_t pLen)
{
int32_t result = TC_FAIL;
uint32_t i;
uint8_t persString[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 */
uint32_t len = pLen;
if (len > sizeof persString)
{
len = sizeof persString;
}
/* 10.2.1.3.1 step 2 */
memcpy(persString, 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] ^= persString[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_SUCCESS;
}
return result;
}
int32_t tc_ctr_prng_reseed(TCCtrPrng_t * const ctx,
uint8_t const entropy[],
uint32_t entropyLen)
{
int32_t result = TC_FAIL;
//todo - add additional input support
/*
* 10.2.1.4.1 steps 1 - 3 not required - no additional input accepted by
* this reseed function
*/
uint32_t seedlen = (uint32_t)TC_AES_KEY_SIZE + (uint32_t)TC_AES_BLOCK_SIZE;
if ((0 != ctx) && (entropyLen == seedlen))
{
/* 10.2.1.4.1 step 4 */
tc_ctr_prng_update(ctx, entropy);
/* 10.2.1.4.1 step 5 */
ctx->reseedCount = 1U;
result = TC_SUCCESS;
}
return result;
}
//todo comment
int32_t tc_ctr_prng_generate(TCCtrPrng_t * const ctx,
uint8_t out[],
uint32_t 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 uint32_t MAX_BYTES_PER_REQ = 65536U;
int32_t result = TC_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_RESEED_REQ;
}
else
{
//todo - add additional input support
/* 10.2.1.5.1 step 2 - no additional input supported, so no action */
/* 10.2.1.5.1 step 3 - implicit */
/* 10.2.1.5.1 step 4 */
uint32_t len = 0U;
while (len < outlen)
{
uint32_t 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, 0);
/* 10.2.1.5.1 step 7 */
ctx->reseedCount++;
/* 10.2.1.5.1 step 8 */
result = TC_SUCCESS;
}
}
return result;
}
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