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trezor-firmware/crypto/tls_prf.c

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/**
* Copyright (c) 2023 Andrew R. Kozlik
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
* OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
/*
* For a specification of TLS-PRF see
* https://datatracker.ietf.org/doc/html/rfc5246#section-5
*/
#include <string.h>
#include "hmac.h"
#include "memzero.h"
#include "sha2.h"
void tls_prf_sha256(const uint8_t *secret, size_t secret_len,
const uint8_t *label, size_t label_len, const uint8_t *seed,
size_t seed_len, uint8_t *output, size_t out_len) {
uint32_t idig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)] = {0};
uint32_t odig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)] = {0};
uint8_t a[SHA256_DIGEST_LENGTH] = {0};
uint8_t result[SHA256_DIGEST_LENGTH] = {0};
SHA256_CTX ctx = {0};
// Prepare inner and outer digest.
hmac_sha256_prepare(secret, secret_len, odig, idig);
// a = HMAC(secret, label + seed)
sha256_Init_ex(&ctx, idig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, label, label_len);
sha256_Update(&ctx, seed, seed_len);
sha256_Final(&ctx, a);
sha256_Init_ex(&ctx, odig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, a, SHA256_DIGEST_LENGTH);
sha256_Final(&ctx, a);
while (1) {
// result = HMAC(secret, a + label + seed)
sha256_Init_ex(&ctx, idig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, a, SHA256_DIGEST_LENGTH);
sha256_Update(&ctx, label, label_len);
sha256_Update(&ctx, seed, seed_len);
sha256_Final(&ctx, result);
sha256_Init_ex(&ctx, odig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, result, SHA256_DIGEST_LENGTH);
sha256_Final(&ctx, result);
if (out_len <= SHA256_DIGEST_LENGTH) {
break;
}
memcpy(output, result, SHA256_DIGEST_LENGTH);
output += SHA256_DIGEST_LENGTH;
out_len -= SHA256_DIGEST_LENGTH;
// a = HMAC(secret, a)
sha256_Init_ex(&ctx, idig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, a, SHA256_DIGEST_LENGTH);
sha256_Final(&ctx, a);
sha256_Init_ex(&ctx, odig, 8 * SHA256_BLOCK_LENGTH);
sha256_Update(&ctx, a, SHA256_DIGEST_LENGTH);
sha256_Final(&ctx, a);
}
memcpy(output, result, out_len);
memzero(idig, sizeof(idig));
memzero(odig, sizeof(odig));
memzero(a, sizeof(a));
memzero(result, sizeof(result));
}