sha256.c

Go to the documentation of this file.

/*
 * 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 "includes.h"

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


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);
}


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);
}


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++;
        }
}