lib/crypto/aes_cmac_128.c

   1 /*
   2    AES-CMAC-128 (rfc 4493)
   3    Copyright (C) Stefan Metzmacher 2012
   4    Copyright (C) Jeremy Allison 2012
   5    Copyright (C) Michael Adam 2012
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21 #include "replace.h"
  22 #include "../lib/crypto/crypto.h"
  23
  24 static const uint8_t const_Zero[] = {
  25         0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
  26         0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00
  27 };
  28
  29 static const uint8_t const_Rb[] = {
  30         0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
  31         0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x87
  32 };
  33
  34 #define _MSB(x) (((x)[0] & 0x80)?1:0)
  35
  36 void aes_cmac_128_init(struct aes_cmac_128_context *ctx,
  37                        const uint8_t K[AES_BLOCK_SIZE])
  38 {
  39         ZERO_STRUCTP(ctx);
  40
  41         AES_set_encrypt_key(K, 128, &ctx->aes_key);
  42
  43         /* step 1 - generate subkeys k1 and k2 */
  44
  45         AES_encrypt(const_Zero, ctx->L, &ctx->aes_key);
  46
  47         if (_MSB(ctx->L) == 0) {
  48                 aes_block_lshift(ctx->L, ctx->K1);
  49         } else {
  50                 aes_block_lshift(ctx->L, ctx->tmp);
  51                 aes_block_xor(ctx->tmp, const_Rb, ctx->K1);
  52         }
  53
  54         if (_MSB(ctx->K1) == 0) {
  55                 aes_block_lshift(ctx->K1, ctx->K2);
  56         } else {
  57                 aes_block_lshift(ctx->K1, ctx->tmp);
  58                 aes_block_xor(ctx->tmp, const_Rb, ctx->K2);
  59         }
  60 }
  61
  62 void aes_cmac_128_update(struct aes_cmac_128_context *ctx,
  63                          const uint8_t *msg, size_t msg_len)
  64 {
  65         /*
  66          * check if we expand the block
  67          */
  68         if (ctx->last_len < AES_BLOCK_SIZE) {
  69                 size_t len = MIN(AES_BLOCK_SIZE - ctx->last_len, msg_len);
  70
  71                 memcpy(&ctx->last[ctx->last_len], msg, len);
  72                 msg += len;
  73                 msg_len -= len;
  74                 ctx->last_len += len;
  75         }
  76
  77         if (msg_len == 0) {
  78                 /* if it is still the last block, we are done */
  79                 return;
  80         }
  81
  82         /*
  83          * now checksum everything but the last block
  84          */
  85         aes_block_xor(ctx->X, ctx->last, ctx->Y);
  86         AES_encrypt(ctx->Y, ctx->X, &ctx->aes_key);
  87
  88         while (msg_len > AES_BLOCK_SIZE) {
  89                 aes_block_xor(ctx->X, msg, ctx->Y);
  90                 AES_encrypt(ctx->Y, ctx->X, &ctx->aes_key);
  91                 msg += AES_BLOCK_SIZE;
  92                 msg_len -= AES_BLOCK_SIZE;
  93         }
  94
  95         /*
  96          * copy the last block, it will be processed in
  97          * aes_cmac_128_final().
  98          */
  99         ZERO_STRUCT(ctx->last);
 100         memcpy(ctx->last, msg, msg_len);
 101         ctx->last_len = msg_len;
 102 }
 103
 104 void aes_cmac_128_final(struct aes_cmac_128_context *ctx,
 105                         uint8_t T[AES_BLOCK_SIZE])
 106 {
 107         if (ctx->last_len < AES_BLOCK_SIZE) {
 108                 ctx->last[ctx->last_len] = 0x80;
 109                 aes_block_xor(ctx->last, ctx->K2, ctx->tmp);
 110         } else {
 111                 aes_block_xor(ctx->last, ctx->K1, ctx->tmp);
 112         }
 113
 114         aes_block_xor(ctx->tmp, ctx->X, ctx->Y);
 115         AES_encrypt(ctx->Y, T, &ctx->aes_key);
 116
 117         ZERO_STRUCTP(ctx);
 118 }