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
  24 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  25
  26 /**
  27  * @file
  28  *
  29  * Keyed-Hashing for Message Authentication
  30  */
  31
  32 #include <string.h>
  33 #include <assert.h>
  34 #include <ipxe/crypto.h>
  35 #include <ipxe/hmac.h>
  36
  37 /**
  38  * Reduce HMAC key length
  39  *
  40  * @v digest            Digest algorithm to use
  41  * @v digest_ctx        Digest context
  42  * @v key               Key
  43  * @v key_len           Length of key
  44  */
  45 static void hmac_reduce_key ( struct digest_algorithm *digest,
  46                               void *key, size_t *key_len ) {
  47         uint8_t digest_ctx[digest->ctxsize];
  48
  49         digest_init ( digest, digest_ctx );
  50         digest_update ( digest, digest_ctx, key, *key_len );
  51         digest_final ( digest, digest_ctx, key );
  52         *key_len = digest->digestsize;
  53 }
  54
  55 /**
  56  * Initialise HMAC
  57  *
  58  * @v digest            Digest algorithm to use
  59  * @v digest_ctx        Digest context
  60  * @v key               Key
  61  * @v key_len           Length of key
  62  *
  63  * The length of the key should be less than the block size of the
  64  * digest algorithm being used.  (If the key length is greater, it
  65  * will be replaced with its own digest, and key_len will be updated
  66  * accordingly).
  67  */
  68 void hmac_init ( struct digest_algorithm *digest, void *digest_ctx,
  69                  void *key, size_t *key_len ) {
  70         unsigned char k_ipad[digest->blocksize];
  71         unsigned int i;
  72
  73         /* Reduce key if necessary */
  74         if ( *key_len > sizeof ( k_ipad ) )
  75                 hmac_reduce_key ( digest, key, key_len );
  76
  77         /* Construct input pad */
  78         memset ( k_ipad, 0, sizeof ( k_ipad ) );
  79         memcpy ( k_ipad, key, *key_len );
  80         for ( i = 0 ; i < sizeof ( k_ipad ) ; i++ ) {
  81                 k_ipad[i] ^= 0x36;
  82         }
  83
  84         /* Start inner hash */
  85         digest_init ( digest, digest_ctx );
  86         digest_update ( digest, digest_ctx, k_ipad, sizeof ( k_ipad ) );
  87 }
  88
  89 /**
  90  * Finalise HMAC
  91  *
  92  * @v digest            Digest algorithm to use
  93  * @v digest_ctx        Digest context
  94  * @v key               Key
  95  * @v key_len           Length of key
  96  * @v hmac              HMAC digest to fill in
  97  *
  98  * The length of the key should be less than the block size of the
  99  * digest algorithm being used.  (If the key length is greater, it
 100  * will be replaced with its own digest, and key_len will be updated
 101  * accordingly).
 102  */
 103 void hmac_final ( struct digest_algorithm *digest, void *digest_ctx,
 104                   void *key, size_t *key_len, void *hmac ) {
 105         unsigned char k_opad[digest->blocksize];
 106         unsigned int i;
 107
 108         /* Reduce key if necessary */
 109         if ( *key_len > sizeof ( k_opad ) )
 110                 hmac_reduce_key ( digest, key, key_len );
 111
 112         /* Construct output pad */
 113         memset ( k_opad, 0, sizeof ( k_opad ) );
 114         memcpy ( k_opad, key, *key_len );
 115         for ( i = 0 ; i < sizeof ( k_opad ) ; i++ ) {
 116                 k_opad[i] ^= 0x5c;
 117         }
 118
 119         /* Finish inner hash */
 120         digest_final ( digest, digest_ctx, hmac );
 121
 122         /* Perform outer hash */
 123         digest_init ( digest, digest_ctx );
 124         digest_update ( digest, digest_ctx, k_opad, sizeof ( k_opad ) );
 125         digest_update ( digest, digest_ctx, hmac, digest->digestsize );
 126         digest_final ( digest, digest_ctx, hmac );
 127 }