diff options
Diffstat (limited to 'chip/g/dcrypto/hkdf.c')
-rw-r--r-- | chip/g/dcrypto/hkdf.c | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/chip/g/dcrypto/hkdf.c b/chip/g/dcrypto/hkdf.c new file mode 100644 index 0000000000..3afdc6b2eb --- /dev/null +++ b/chip/g/dcrypto/hkdf.c @@ -0,0 +1,83 @@ +/* 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" + +#include "cryptoc/sha256.h" +#include "cryptoc/util.h" + +static int hkdf_extract(uint8_t *PRK, const uint8_t *salt, size_t salt_len, + const uint8_t *IKM, size_t IKM_len) +{ + LITE_HMAC_CTX ctx; + + if (PRK == NULL) + return 0; + if (salt == NULL && salt_len > 0) + return 0; + if (IKM == NULL && IKM_len > 0) + return 0; + + DCRYPTO_HMAC_SHA256_init(&ctx, salt, salt_len); + HASH_update(&ctx.hash, IKM, IKM_len); + memcpy(PRK, DCRYPTO_HMAC_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) { + LITE_HMAC_CTX ctx; + const size_t block_size = OKM_len < SHA256_DIGEST_SIZE ? + OKM_len : SHA256_DIGEST_SIZE; + + DCRYPTO_HMAC_SHA256_init(&ctx, PRK, SHA256_DIGEST_SIZE); + HASH_update(&ctx.hash, T, T_len); + HASH_update(&ctx.hash, info, info_len); + HASH_update(&ctx.hash, &count, sizeof(count)); + memcpy(OKM, DCRYPTO_HMAC_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; +} |