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      1 /*
      2  * SHA1 T-PRF for EAP-FAST
      3  * Copyright (c) 2003-2005, Jouni Malinen <j (at) w1.fi>
      4  *
      5  * This software may be distributed under the terms of the BSD license.
      6  * See README for more details.
      7  */
      8 
      9 #include "includes.h"
     10 
     11 #include "common.h"
     12 #include "sha1.h"
     13 #include "crypto.h"
     14 
     15 /**
     16  * sha1_t_prf - EAP-FAST Pseudo-Random Function (T-PRF)
     17  * @key: Key for PRF
     18  * @key_len: Length of the key in bytes
     19  * @label: A unique label for each purpose of the PRF
     20  * @seed: Seed value to bind into the key
     21  * @seed_len: Length of the seed
     22  * @buf: Buffer for the generated pseudo-random key
     23  * @buf_len: Number of bytes of key to generate
     24  * Returns: 0 on success, -1 of failure
     25  *
     26  * This function is used to derive new, cryptographically separate keys from a
     27  * given key for EAP-FAST. T-PRF is defined in RFC 4851, Section 5.5.
     28  */
     29 int sha1_t_prf(const u8 *key, size_t key_len, const char *label,
     30 	       const u8 *seed, size_t seed_len, u8 *buf, size_t buf_len)
     31 {
     32 	unsigned char counter = 0;
     33 	size_t pos, plen;
     34 	u8 hash[SHA1_MAC_LEN];
     35 	size_t label_len = os_strlen(label);
     36 	u8 output_len[2];
     37 	const unsigned char *addr[5];
     38 	size_t len[5];
     39 
     40 	addr[0] = hash;
     41 	len[0] = 0;
     42 	addr[1] = (unsigned char *) label;
     43 	len[1] = label_len + 1;
     44 	addr[2] = seed;
     45 	len[2] = seed_len;
     46 	addr[3] = output_len;
     47 	len[3] = 2;
     48 	addr[4] = &counter;
     49 	len[4] = 1;
     50 
     51 	output_len[0] = (buf_len >> 8) & 0xff;
     52 	output_len[1] = buf_len & 0xff;
     53 	pos = 0;
     54 	while (pos < buf_len) {
     55 		counter++;
     56 		plen = buf_len - pos;
     57 		if (hmac_sha1_vector(key, key_len, 5, addr, len, hash))
     58 			return -1;
     59 		if (plen >= SHA1_MAC_LEN) {
     60 			os_memcpy(&buf[pos], hash, SHA1_MAC_LEN);
     61 			pos += SHA1_MAC_LEN;
     62 		} else {
     63 			os_memcpy(&buf[pos], hash, plen);
     64 			break;
     65 		}
     66 		len[0] = SHA1_MAC_LEN;
     67 	}
     68 
     69 	return 0;
     70 }
     71