src/gsm/kdf/sha256.c

/*
 * SHA-256 hash implementation and interface functions
 * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */


#include "common.h"
#include "sha256.h"
#include "crypto.h"


/**
 * hmac_sha256_vector - HMAC-SHA256 over data vector (RFC 2104)
 * @key: Key for HMAC operations
 * @key_len: Length of the key in bytes
 * @num_elem: Number of elements in the data vector
 * @addr: Pointers to the data areas
 * @len: Lengths of the data blocks
 * @mac: Buffer for the hash (32 bytes)
 */
void hmac_sha256_vector(const u8 *key, size_t key_len, size_t num_elem,
			const u8 *addr[], const size_t *len, u8 *mac)
{
	unsigned char k_pad[64]; /* padding - key XORd with ipad/opad */
	unsigned char tk[32];
	const u8 *_addr[6];
	size_t _len[6], i;

	if (num_elem > 5) {
		/*
		 * Fixed limit on the number of fragments to avoid having to
		 * allocate memory (which could fail).
		 */
		return;
	}

        /* if key is longer than 64 bytes reset it to key = SHA256(key) */
        if (key_len > 64) {
		sha256_vector(1, &key, &key_len, tk);
		key = tk;
		key_len = 32;
        }

	/* the HMAC_SHA256 transform looks like:
	 *
	 * SHA256(K XOR opad, SHA256(K XOR ipad, text))
	 *
	 * where K is an n byte key
	 * ipad is the byte 0x36 repeated 64 times
	 * opad is the byte 0x5c repeated 64 times
	 * and text is the data being protected */

	/* start out by storing key in ipad */
	os_memset(k_pad, 0, sizeof(k_pad));
	os_memcpy(k_pad, key, key_len);
	/* XOR key with ipad values */
	for (i = 0; i < 64; i++)
		k_pad[i] ^= 0x36;

	/* perform inner SHA256 */
	_addr[0] = k_pad;
	_len[0] = 64;
	for (i = 0; i < num_elem; i++) {
		_addr[i + 1] = addr[i];
		_len[i + 1] = len[i];
	}
	sha256_vector(1 + num_elem, _addr, _len, mac);

	os_memset(k_pad, 0, sizeof(k_pad));
	os_memcpy(k_pad, key, key_len);
	/* XOR key with opad values */
	for (i = 0; i < 64; i++)
		k_pad[i] ^= 0x5c;

	/* perform outer SHA256 */
	_addr[0] = k_pad;
	_len[0] = 64;
	_addr[1] = mac;
	_len[1] = SHA256_MAC_LEN;
	sha256_vector(2, _addr, _len, mac);
}


/**
 * hmac_sha256 - HMAC-SHA256 over data buffer (RFC 2104)
 * @key: Key for HMAC operations
 * @key_len: Length of the key in bytes
 * @data: Pointers to the data area
 * @data_len: Length of the data area
 * @mac: Buffer for the hash (20 bytes)
 */
void hmac_sha256(const u8 *key, size_t key_len, const u8 *data,
		 size_t data_len, u8 *mac)
{
	hmac_sha256_vector(key, key_len, 1, &data, &data_len, mac);
}


/**
 * sha256_prf - SHA256-based Pseudo-Random Function (IEEE 802.11r, 8.5.1.5.2)
 * @key: Key for PRF
 * @key_len: Length of the key in bytes
 * @label: A unique label for each purpose of the PRF
 * @data: Extra data to bind into the key
 * @data_len: Length of the data
 * @buf: Buffer for the generated pseudo-random key
 * @buf_len: Number of bytes of key to generate
 *
 * This function is used to derive new, cryptographically separate keys from a
 * given key.
 */
void sha256_prf(const u8 *key, size_t key_len, const char *label,
		const u8 *data, size_t data_len, u8 *buf, size_t buf_len)
{
	u16 counter = 1;
	size_t pos, plen;
	u8 hash[SHA256_MAC_LEN];
	const u8 *addr[4];
	size_t len[4];
	u8 counter_le[2], length_le[2];

	addr[0] = counter_le;
	len[0] = 2;
	addr[1] = (u8 *) label;
	len[1] = os_strlen(label);
	addr[2] = data;
	len[2] = data_len;
	addr[3] = length_le;
	len[3] = sizeof(length_le);

	WPA_PUT_LE16(length_le, buf_len * 8);
	pos = 0;
	while (pos < buf_len) {
		plen = buf_len - pos;
		WPA_PUT_LE16(counter_le, counter);
		if (plen >= SHA256_MAC_LEN) {
			hmac_sha256_vector(key, key_len, 4, addr, len,
					   &buf[pos]);
			pos += SHA256_MAC_LEN;
		} else {
			hmac_sha256_vector(key, key_len, 4, addr, len, hash);
			os_memcpy(&buf[pos], hash, plen);
			break;
		}
		counter++;
	}
}