/* Copyright (c) 2017, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <openssl/rand.h>
#include <openssl/type_check.h>
#include <openssl/mem.h>
#include "internal.h"
#include "../cipher/internal.h"
// Section references in this file refer to SP 800-90Ar1:
// http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-90Ar1.pdf
// See table 3.
static const uint64_t kMaxReseedCount = UINT64_C(1) << 48;
int CTR_DRBG_init(CTR_DRBG_STATE *drbg,
const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],
const uint8_t *personalization, size_t personalization_len) {
// Section 10.2.1.3.1
if (personalization_len > CTR_DRBG_ENTROPY_LEN) {
return 0;
}
uint8_t seed_material[CTR_DRBG_ENTROPY_LEN];
OPENSSL_memcpy(seed_material, entropy, CTR_DRBG_ENTROPY_LEN);
for (size_t i = 0; i < personalization_len; i++) {
seed_material[i] ^= personalization[i];
}
// Section 10.2.1.2
// kInitMask is the result of encrypting blocks with big-endian value 1, 2
// and 3 with the all-zero AES-256 key.
static const uint8_t kInitMask[CTR_DRBG_ENTROPY_LEN] = {
0x53, 0x0f, 0x8a, 0xfb, 0xc7, 0x45, 0x36, 0xb9, 0xa9, 0x63, 0xb4, 0xf1,
0xc4, 0xcb, 0x73, 0x8b, 0xce, 0xa7, 0x40, 0x3d, 0x4d, 0x60, 0x6b, 0x6e,
0x07, 0x4e, 0xc5, 0xd3, 0xba, 0xf3, 0x9d, 0x18, 0x72, 0x60, 0x03, 0xca,
0x37, 0xa6, 0x2a, 0x74, 0xd1, 0xa2, 0xf5, 0x8e, 0x75, 0x06, 0x35, 0x8e,
};
for (size_t i = 0; i < sizeof(kInitMask); i++) {
seed_material[i] ^= kInitMask[i];
}
drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, seed_material, 32);
OPENSSL_memcpy(drbg->counter.bytes, seed_material + 32, 16);
drbg->reseed_counter = 1;
return 1;
}
OPENSSL_STATIC_ASSERT(CTR_DRBG_ENTROPY_LEN % AES_BLOCK_SIZE == 0,
"not a multiple of AES block size");
// ctr_inc adds |n| to the last four bytes of |drbg->counter|, treated as a
// big-endian number.
static void ctr32_add(CTR_DRBG_STATE *drbg, uint32_t n) {
drbg->counter.words[3] =
CRYPTO_bswap4(CRYPTO_bswap4(drbg->counter.words[3]) + n);
}
static int ctr_drbg_update(CTR_DRBG_STATE *drbg, const uint8_t *data,
size_t data_len) {
// Per section 10.2.1.2, |data_len| must be |CTR_DRBG_ENTROPY_LEN|. Here, we
// allow shorter inputs and right-pad them with zeros. This is equivalent to
// the specified algorithm but saves a copy in |CTR_DRBG_generate|.
if (data_len > CTR_DRBG_ENTROPY_LEN) {
return 0;
}
uint8_t temp[CTR_DRBG_ENTROPY_LEN];
for (size_t i = 0; i < CTR_DRBG_ENTROPY_LEN; i += AES_BLOCK_SIZE) {
ctr32_add(drbg, 1);
drbg->block(drbg->counter.bytes, temp + i, &drbg->ks);
}
for (size_t i = 0; i < data_len; i++) {
temp[i] ^= data[i];
}
drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, temp, 32);
OPENSSL_memcpy(drbg->counter.bytes, temp + 32, 16);
return 1;
}
int CTR_DRBG_reseed(CTR_DRBG_STATE *drbg,
const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],
const uint8_t *additional_data,
size_t additional_data_len) {
// Section 10.2.1.4
uint8_t entropy_copy[CTR_DRBG_ENTROPY_LEN];
if (additional_data_len > 0) {
if (additional_data_len > CTR_DRBG_ENTROPY_LEN) {
return 0;
}
OPENSSL_memcpy(entropy_copy, entropy, CTR_DRBG_ENTROPY_LEN);
for (size_t i = 0; i < additional_data_len; i++) {
entropy_copy[i] ^= additional_data[i];
}
entropy = entropy_copy;
}
if (!ctr_drbg_update(drbg, entropy, CTR_DRBG_ENTROPY_LEN)) {
return 0;
}
drbg->reseed_counter = 1;
return 1;
}
int CTR_DRBG_generate(CTR_DRBG_STATE *drbg, uint8_t *out, size_t out_len,
const uint8_t *additional_data,
size_t additional_data_len) {
// See 9.3.1
if (out_len > CTR_DRBG_MAX_GENERATE_LENGTH) {
return 0;
}
// See 10.2.1.5.1
if (drbg->reseed_counter > kMaxReseedCount) {
return 0;
}
if (additional_data_len != 0 &&
!ctr_drbg_update(drbg, additional_data, additional_data_len)) {
return 0;
}
// kChunkSize is used to interact better with the cache. Since the AES-CTR
// code assumes that it's encrypting rather than just writing keystream, the
// buffer has to be zeroed first. Without chunking, large reads would zero
// the whole buffer, flushing the L1 cache, and then do another pass (missing
// the cache every time) to “encrypt” it. The code can avoid this by
// chunking.
static const size_t kChunkSize = 8 * 1024;
while (out_len >= AES_BLOCK_SIZE) {
size_t todo = kChunkSize;
if (todo > out_len) {
todo = out_len;
}
todo &= ~(AES_BLOCK_SIZE-1);
const size_t num_blocks = todo / AES_BLOCK_SIZE;
if (drbg->ctr) {
OPENSSL_memset(out, 0, todo);
ctr32_add(drbg, 1);
drbg->ctr(out, out, num_blocks, &drbg->ks, drbg->counter.bytes);
ctr32_add(drbg, num_blocks - 1);
} else {
for (size_t i = 0; i < todo; i += AES_BLOCK_SIZE) {
ctr32_add(drbg, 1);
drbg->block(drbg->counter.bytes, out + i, &drbg->ks);
}
}
out += todo;
out_len -= todo;
}
if (out_len > 0) {
uint8_t block[AES_BLOCK_SIZE];
ctr32_add(drbg, 1);
drbg->block(drbg->counter.bytes, block, &drbg->ks);
OPENSSL_memcpy(out, block, out_len);
}
// Right-padding |additional_data| in step 2.2 is handled implicitly by
// |ctr_drbg_update|, to save a copy.
if (!ctr_drbg_update(drbg, additional_data, additional_data_len)) {
return 0;
}
drbg->reseed_counter++;
return 1;
}
void CTR_DRBG_clear(CTR_DRBG_STATE *drbg) {
OPENSSL_cleanse(drbg, sizeof(CTR_DRBG_STATE));
}