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/*
* SHA256-based PRF (IEEE 802.11r)
* Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#include "includes.h"
#include "common.h"
#include "sha256.h"
#include "crypto.h"
/**
* 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++;
}
}
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