1 /*
2 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19 FILE_LICENCE ( GPL2_OR_LATER );
20
21 /**
22 * @file
23 *
24 * Keyed-Hashing for Message Authentication
25 */
26
27 #include <string.h>
28 #include <assert.h>
29 #include <gpxe/crypto.h>
30 #include <gpxe/hmac.h>
31
32 /**
33 * Reduce HMAC key length
34 *
35 * @v digest Digest algorithm to use
36 * @v digest_ctx Digest context
37 * @v key Key
38 * @v key_len Length of key
39 */
hmac_reduce_key(struct digest_algorithm * digest,void * key,size_t * key_len)40 static void hmac_reduce_key ( struct digest_algorithm *digest,
41 void *key, size_t *key_len ) {
42 uint8_t digest_ctx[digest->ctxsize];
43
44 digest_init ( digest, digest_ctx );
45 digest_update ( digest, digest_ctx, key, *key_len );
46 digest_final ( digest, digest_ctx, key );
47 *key_len = digest->digestsize;
48 }
49
50 /**
51 * Initialise HMAC
52 *
53 * @v digest Digest algorithm to use
54 * @v digest_ctx Digest context
55 * @v key Key
56 * @v key_len Length of key
57 *
58 * The length of the key should be less than the block size of the
59 * digest algorithm being used. (If the key length is greater, it
60 * will be replaced with its own digest, and key_len will be updated
61 * accordingly).
62 */
hmac_init(struct digest_algorithm * digest,void * digest_ctx,void * key,size_t * key_len)63 void hmac_init ( struct digest_algorithm *digest, void *digest_ctx,
64 void *key, size_t *key_len ) {
65 unsigned char k_ipad[digest->blocksize];
66 unsigned int i;
67
68 /* Reduce key if necessary */
69 if ( *key_len > sizeof ( k_ipad ) )
70 hmac_reduce_key ( digest, key, key_len );
71
72 /* Construct input pad */
73 memset ( k_ipad, 0, sizeof ( k_ipad ) );
74 memcpy ( k_ipad, key, *key_len );
75 for ( i = 0 ; i < sizeof ( k_ipad ) ; i++ ) {
76 k_ipad[i] ^= 0x36;
77 }
78
79 /* Start inner hash */
80 digest_init ( digest, digest_ctx );
81 digest_update ( digest, digest_ctx, k_ipad, sizeof ( k_ipad ) );
82 }
83
84 /**
85 * Finalise HMAC
86 *
87 * @v digest Digest algorithm to use
88 * @v digest_ctx Digest context
89 * @v key Key
90 * @v key_len Length of key
91 * @v hmac HMAC digest to fill in
92 *
93 * The length of the key should be less than the block size of the
94 * digest algorithm being used. (If the key length is greater, it
95 * will be replaced with its own digest, and key_len will be updated
96 * accordingly).
97 */
hmac_final(struct digest_algorithm * digest,void * digest_ctx,void * key,size_t * key_len,void * hmac)98 void hmac_final ( struct digest_algorithm *digest, void *digest_ctx,
99 void *key, size_t *key_len, void *hmac ) {
100 unsigned char k_opad[digest->blocksize];
101 unsigned int i;
102
103 /* Reduce key if necessary */
104 if ( *key_len > sizeof ( k_opad ) )
105 hmac_reduce_key ( digest, key, key_len );
106
107 /* Construct output pad */
108 memset ( k_opad, 0, sizeof ( k_opad ) );
109 memcpy ( k_opad, key, *key_len );
110 for ( i = 0 ; i < sizeof ( k_opad ) ; i++ ) {
111 k_opad[i] ^= 0x5c;
112 }
113
114 /* Finish inner hash */
115 digest_final ( digest, digest_ctx, hmac );
116
117 /* Perform outer hash */
118 digest_init ( digest, digest_ctx );
119 digest_update ( digest, digest_ctx, k_opad, sizeof ( k_opad ) );
120 digest_update ( digest, digest_ctx, hmac, digest->digestsize );
121 digest_final ( digest, digest_ctx, hmac );
122 }
123