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/* Copyright 2016 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
/* An implementation of HKDF as per RFC 5869. */
#include "dcrypto.h"
#include "internal.h"
static int hkdf_extract(uint8_t *PRK, const uint8_t *salt, size_t salt_len,
const uint8_t *IKM, size_t IKM_len)
{
struct hmac_sha256_ctx ctx;
if (PRK == NULL)
return 0;
if (salt == NULL && salt_len > 0)
return 0;
if (IKM == NULL && IKM_len > 0)
return 0;
HMAC_SHA256_hw_init(&ctx, salt, salt_len);
HMAC_SHA256_update(&ctx, IKM, IKM_len);
memcpy(PRK, HMAC_SHA256_hw_final(&ctx), SHA256_DIGEST_SIZE);
return 1;
}
static int hkdf_expand(uint8_t *OKM, size_t OKM_len, const uint8_t *PRK,
const uint8_t *info, size_t info_len)
{
uint8_t count = 1;
const uint8_t *T = OKM;
size_t T_len = 0;
uint32_t num_blocks = (OKM_len / SHA256_DIGEST_SIZE) +
(OKM_len % SHA256_DIGEST_SIZE ? 1 : 0);
if (OKM == NULL || OKM_len == 0)
return 0;
if (PRK == NULL)
return 0;
if (info == NULL && info_len > 0)
return 0;
if (num_blocks > 255)
return 0;
while (OKM_len > 0) {
struct hmac_sha256_ctx ctx;
const size_t block_size = OKM_len < SHA256_DIGEST_SIZE ?
OKM_len : SHA256_DIGEST_SIZE;
HMAC_SHA256_hw_init(&ctx, PRK, SHA256_DIGEST_SIZE);
HMAC_SHA256_update(&ctx, T, T_len);
HMAC_SHA256_update(&ctx, info, info_len);
HMAC_SHA256_update(&ctx, &count, sizeof(count));
memcpy(OKM, HMAC_SHA256_hw_final(&ctx), block_size);
T += T_len;
T_len = SHA256_DIGEST_SIZE;
count += 1;
OKM += block_size;
OKM_len -= block_size;
}
return 1;
}
int DCRYPTO_hkdf(uint8_t *OKM, size_t OKM_len,
const uint8_t *salt, size_t salt_len,
const uint8_t *IKM, size_t IKM_len,
const uint8_t *info, size_t info_len)
{
int result;
uint8_t PRK[SHA256_DIGEST_SIZE];
if (!hkdf_extract(PRK, salt, salt_len, IKM, IKM_len))
return 0;
result = hkdf_expand(OKM, OKM_len, PRK, info, info_len);
always_memset(PRK, 0, sizeof(PRK));
return result;
}
#ifdef CRYPTO_TEST_SETUP
#include "extension.h"
enum {
TEST_RFC = 0,
};
#define MAX_OKM_BYTES 1024
static void hkdf_command_handler(void *cmd_body,
size_t cmd_size,
size_t *response_size)
{
uint8_t *cmd;
uint8_t *out;
uint8_t op;
size_t salt_len;
const uint8_t *salt;
size_t IKM_len;
const uint8_t *IKM;
size_t info_len;
const uint8_t *info;
size_t OKM_len;
uint8_t OKM[MAX_OKM_BYTES];
/* Command format.
*
* WIDTH FIELD
* 1 OP
* 1 MSB SALT LEN
* 1 LSB SALT LEN
* SALT_LEN SALT
* 1 MSB IKM LEN
* 1 LSB IKM LEN
* IKM_LEN IKM
* 1 MSB INFO LEN
* 1 LSB INFO LEN
* INFO_LEN INFO
* 1 MSB OKM LEN
* 1 LSB OKM LEN
*/
cmd = (uint8_t *) cmd_body;
out = (uint8_t *) cmd_body;
op = *cmd++;
salt_len = ((uint16_t) (cmd[0] << 8)) | cmd[1];
cmd += 2;
salt = cmd;
cmd += salt_len;
IKM_len = ((uint16_t) (cmd[0] << 8)) | cmd[1];
cmd += 2;
IKM = cmd;
cmd += IKM_len;
info_len = ((uint16_t) (cmd[0] << 8)) | cmd[1];
cmd += 2;
info = cmd;
cmd += info_len;
OKM_len = ((uint16_t) (cmd[0] << 8)) | cmd[1];
if (OKM_len > MAX_OKM_BYTES) {
*response_size = 0;
return;
}
switch (op) {
case TEST_RFC:
if (DCRYPTO_hkdf(OKM, OKM_len, salt, salt_len,
IKM, IKM_len, info, info_len)) {
memcpy(out, OKM, OKM_len);
*response_size = OKM_len;
} else {
*response_size = 0;
}
break;
default:
*response_size = 0;
}
}
DECLARE_EXTENSION_COMMAND(EXTENSION_HKDF, hkdf_command_handler);
#endif /* CRYPTO_TEST_SETUP */
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