src/crypto/hmac.c

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  17  * 02110-1301, USA.
  18  *
  19  * You can also choose to distribute this program under the terms of
  20  * the Unmodified Binary Distribution Licence (as given in the file
  21  * COPYING.UBDL), provided that you have satisfied its requirements.
  22  *
  23  * Alternatively, you may distribute this code in source or binary
  24  * form, with or without modification, provided that the following
  25  * conditions are met:
  26  *
  27  *  1. Redistributions of source code must retain the above copyright
  28  *     notice, this list of conditions and the above disclaimer.
  29  *
  30  *  2. Redistributions in binary form must reproduce the above
  31  *     copyright notice, this list of conditions and the above
  32  *     disclaimer in the documentation and/or other materials provided
  33  *     with the distribution.
  34  */
  35
  36 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  37
  38 /**
  39  * @file
  40  *
  41  * Keyed-Hashing for Message Authentication
  42  */
  43
  44 #include <string.h>
  45 #include <assert.h>
  46 #include <ipxe/crypto.h>
  47 #include <ipxe/hmac.h>
  48
  49 /**
  50  * Reduce HMAC key length
  51  *
  52  * @v digest            Digest algorithm to use
  53  * @v digest_ctx        Digest context
  54  * @v key               Key
  55  * @v key_len           Length of key
  56  */
  57 static void hmac_reduce_key ( struct digest_algorithm *digest,
  58                               void *key, size_t *key_len ) {
  59         uint8_t digest_ctx[digest->ctxsize];
  60
  61         digest_init ( digest, digest_ctx );
  62         digest_update ( digest, digest_ctx, key, *key_len );
  63         digest_final ( digest, digest_ctx, key );
  64         *key_len = digest->digestsize;
  65 }
  66
  67 /**
  68  * Initialise HMAC
  69  *
  70  * @v digest            Digest algorithm to use
  71  * @v digest_ctx        Digest context
  72  * @v key               Key
  73  * @v key_len           Length of key
  74  *
  75  * The length of the key should be less than the block size of the
  76  * digest algorithm being used.  (If the key length is greater, it
  77  * will be replaced with its own digest, and key_len will be updated
  78  * accordingly).
  79  */
  80 void hmac_init ( struct digest_algorithm *digest, void *digest_ctx,
  81                  void *key, size_t *key_len ) {
  82         unsigned char k_ipad[digest->blocksize];
  83         unsigned int i;
  84
  85         /* Reduce key if necessary */
  86         if ( *key_len > sizeof ( k_ipad ) )
  87                 hmac_reduce_key ( digest, key, key_len );
  88
  89         /* Construct input pad */
  90         memset ( k_ipad, 0, sizeof ( k_ipad ) );
  91         memcpy ( k_ipad, key, *key_len );
  92         for ( i = 0 ; i < sizeof ( k_ipad ) ; i++ ) {
  93                 k_ipad[i] ^= 0x36;
  94         }
  95
  96         /* Start inner hash */
  97         digest_init ( digest, digest_ctx );
  98         digest_update ( digest, digest_ctx, k_ipad, sizeof ( k_ipad ) );
  99 }
 100
 101 /**
 102  * Finalise HMAC
 103  *
 104  * @v digest            Digest algorithm to use
 105  * @v digest_ctx        Digest context
 106  * @v key               Key
 107  * @v key_len           Length of key
 108  * @v hmac              HMAC digest to fill in
 109  *
 110  * The length of the key should be less than the block size of the
 111  * digest algorithm being used.  (If the key length is greater, it
 112  * will be replaced with its own digest, and key_len will be updated
 113  * accordingly).
 114  */
 115 void hmac_final ( struct digest_algorithm *digest, void *digest_ctx,
 116                   void *key, size_t *key_len, void *hmac ) {
 117         unsigned char k_opad[digest->blocksize];
 118         unsigned int i;
 119
 120         /* Reduce key if necessary */
 121         if ( *key_len > sizeof ( k_opad ) )
 122                 hmac_reduce_key ( digest, key, key_len );
 123
 124         /* Construct output pad */
 125         memset ( k_opad, 0, sizeof ( k_opad ) );
 126         memcpy ( k_opad, key, *key_len );
 127         for ( i = 0 ; i < sizeof ( k_opad ) ; i++ ) {
 128                 k_opad[i] ^= 0x5c;
 129         }
 130
 131         /* Finish inner hash */
 132         digest_final ( digest, digest_ctx, hmac );
 133
 134         /* Perform outer hash */
 135         digest_init ( digest, digest_ctx );
 136         digest_update ( digest, digest_ctx, k_opad, sizeof ( k_opad ) );
 137         digest_update ( digest, digest_ctx, hmac, digest->digestsize );
 138         digest_final ( digest, digest_ctx, hmac );
 139 }