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Extend hmac_sha256_kdf() to support HKDF-Expand() as defined in RFC 5869

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The KDF define in RFC 5295 is very similar to HKDF-Expand() defined in
RFC 5869. Allow a NULL label to be used to select the RFC 5869 version
with arbitrary seed (info in RFC 5869) material without forcing the
label and NULL termination to be included. HKDF-Expand() will be needed
for OWE.

Signed-off-by: Jouni Malinen <j@w1.fi>
This commit is contained in:
Jouni Malinen 2017-03-11 22:38:47 +02:00
parent ae1ec1aaf2
commit 4ec833daf8
1 changed files with 14 additions and 6 deletions
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20
src/crypto/sha256-kdf.c
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@ -1,6 +1,6 @@
/*
* HMAC-SHA256 KDF (RFC 5295)
* Copyright (c) 2014, Jouni Malinen <j@w1.fi>
* HMAC-SHA256 KDF (RFC 5295) and HKDF-Expand(SHA256) (RFC 5869)
* Copyright (c) 2014-2017, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
@ -16,7 +16,8 @@
* hmac_sha256_kdf - HMAC-SHA256 based KDF (RFC 5295)
* @secret: Key for KDF
* @secret_len: Length of the key in bytes
* @label: A unique label for each purpose of the KDF
* @label: A unique label for each purpose of the KDF or %NULL to select
* RFC 5869 HKDF-Expand() with arbitrary seed (= info)
* @seed: Seed value to bind into the key
* @seed_len: Length of the seed
* @out: Buffer for the generated pseudo-random key
@ -24,7 +25,9 @@
* Returns: 0 on success, -1 on failure.
*
* This function is used to derive new, cryptographically separate keys from a
* given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2.
* given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2. When used
* with label = NULL and seed = info, this matches HKDF-Expand() defined in
* RFC 5869, Chapter 2.3.
*/
int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
const char *label, const u8 *seed, size_t seed_len,
@ -38,8 +41,13 @@ int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
addr[0] = T;
len[0] = SHA256_MAC_LEN;
addr[1] = (const unsigned char *) label;
len[1] = os_strlen(label) + 1;
if (label) {
addr[1] = (const unsigned char *) label;
len[1] = os_strlen(label) + 1;
} else {
addr[1] = (const u8 *) "";
len[1] = 0;
}
addr[2] = seed;
len[2] = seed_len;
addr[3] = &iter;