src/crypto/aes_wrap.c

   1 /*
   2  * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
   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 #include <stdlib.h>
  22 #include <string.h>
  23 #include <gpxe/crypto.h>
  24 #include <gpxe/aes.h>
  25
  26 /**
  27  * Wrap a key or other data using AES Key Wrap (RFC 3394)
  28  *
  29  * @v kek       Key Encryption Key, 16 bytes
  30  * @v src       Data to encrypt
  31  * @v nblk      Number of 8-byte blocks in @a data
  32  * @ret dest    Encrypted data (8 bytes longer than input)
  33  *
  34  * The algorithm is implemented such that @a src and @a dest may point
  35  * to the same buffer.
  36  */
  37 int aes_wrap ( const void *kek, const void *src, void *dest, int nblk )
  38 {
  39         u8 *A = dest;
  40         u8 B[16];
  41         u8 *R;
  42         int i, j;
  43         void *aes_ctx = malloc ( AES_CTX_SIZE );
  44
  45         if ( ! aes_ctx )
  46                 return -1;
  47
  48         cipher_setkey ( &aes_algorithm, aes_ctx, kek, 16 );
  49
  50         /* Set up */
  51         memset ( A, 0xA6, sizeof ( A ) );
  52         memmove ( dest + 8, src, nblk * 8 );
  53
  54         /* Wrap */
  55         for ( j = 0; j < 6; j++ ) {
  56                 R = dest + 8;
  57                 for ( i = 1; i <= nblk; i++ ) {
  58                         memcpy ( B, A, 8 );
  59                         memcpy ( B + 8, R, 8 );
  60                         cipher_encrypt ( &aes_algorithm, aes_ctx, B, B, 16 );
  61                         memcpy ( A, B, 8 );
  62                         A[7] ^= ( nblk * j ) + i;
  63                         memcpy ( R, B + 8, 8 );
  64                         R += 8;
  65                 }
  66         }
  67
  68         free ( aes_ctx );
  69         return 0;
  70 }
  71
  72 /**
  73  * Unwrap a key or other data using AES Key Wrap (RFC 3394)
  74  *
  75  * @v kek       Key Encryption Key, 16 bytes
  76  * @v src       Data to decrypt
  77  * @v nblk      Number of 8-byte blocks in @e plaintext key
  78  * @ret dest    Decrypted data (8 bytes shorter than input)
  79  * @ret rc      Zero on success, nonzero on IV mismatch
  80  *
  81  * The algorithm is implemented such that @a src and @a dest may point
  82  * to the same buffer.
  83  */
  84 int aes_unwrap ( const void *kek, const void *src, void *dest, int nblk )
  85 {
  86         u8 A[8], B[16];
  87         u8 *R;
  88         int i, j;
  89         void *aes_ctx = malloc ( AES_CTX_SIZE );
  90
  91         if ( ! aes_ctx )
  92                 return -1;
  93
  94         cipher_setkey ( &aes_algorithm, aes_ctx, kek, 16 );
  95
  96         /* Set up */
  97         memcpy ( A, src, 8 );
  98         memmove ( dest, src + 8, nblk * 8 );
  99
 100         /* Unwrap */
 101         for ( j = 5; j >= 0; j-- ) {
 102                 R = dest + ( nblk - 1 ) * 8;
 103                 for ( i = nblk; i >= 1; i-- ) {
 104                         memcpy ( B, A, 8 );
 105                         memcpy ( B + 8, R, 8 );
 106                         B[7] ^= ( nblk * j ) + i;
 107                         cipher_decrypt ( &aes_algorithm, aes_ctx, B, B, 16 );
 108                         memcpy ( A, B, 8 );
 109                         memcpy ( R, B + 8, 8 );
 110                         R -= 8;
 111                 }
 112         }
 113
 114         free ( aes_ctx );
 115
 116         /* Check IV */
 117         for ( i = 0; i < 8; i++ ) {
 118                 if ( A[i] != 0xA6 )
 119                         return -1;
 120         }
 121
 122         return 0;
 123 }