_ Git - BearSSL/blob - src/symcipher/aes_ct_cbcdec.c

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "inner.h"
  26
  27 /* see bearssl_block.h */
  28 void
  29 br_aes_ct_cbcdec_init(br_aes_ct_cbcdec_keys *ctx,
  30         const void *key, size_t len)
  31 {
  32         ctx->vtable = &br_aes_ct_cbcdec_vtable;
  33         ctx->num_rounds = br_aes_ct_keysched(ctx->skey, key, len);
  34 }
  35
  36 /* see bearssl_block.h */
  37 void
  38 br_aes_ct_cbcdec_run(const br_aes_ct_cbcdec_keys *ctx,
  39         void *iv, void *data, size_t len)
  40 {
  41         unsigned char *buf, *ivbuf;
  42         uint32_t iv0, iv1, iv2, iv3;
  43         uint32_t sk_exp[120];
  44
  45         br_aes_ct_skey_expand(sk_exp, ctx->num_rounds, ctx->skey);
  46         ivbuf = iv;
  47         iv0 = br_dec32le(ivbuf);
  48         iv1 = br_dec32le(ivbuf + 4);
  49         iv2 = br_dec32le(ivbuf + 8);
  50         iv3 = br_dec32le(ivbuf + 12);
  51         buf = data;
  52         while (len > 0) {
  53                 uint32_t q[8], sq[8];
  54
  55                 q[0] = br_dec32le(buf);
  56                 q[2] = br_dec32le(buf + 4);
  57                 q[4] = br_dec32le(buf + 8);
  58                 q[6] = br_dec32le(buf + 12);
  59                 if (len >= 32) {
  60                         q[1] = br_dec32le(buf + 16);
  61                         q[3] = br_dec32le(buf + 20);
  62                         q[5] = br_dec32le(buf + 24);
  63                         q[7] = br_dec32le(buf + 28);
  64                 } else {
  65                         q[1] = 0;
  66                         q[3] = 0;
  67                         q[5] = 0;
  68                         q[7] = 0;
  69                 }
  70                 memcpy(sq, q, sizeof q);
  71                 br_aes_ct_ortho(q);
  72                 br_aes_ct_bitslice_decrypt(ctx->num_rounds, sk_exp, q);
  73                 br_aes_ct_ortho(q);
  74                 br_enc32le(buf, q[0] ^ iv0);
  75                 br_enc32le(buf + 4, q[2] ^ iv1);
  76                 br_enc32le(buf + 8, q[4] ^ iv2);
  77                 br_enc32le(buf + 12, q[6] ^ iv3);
  78                 if (len < 32) {
  79                         iv0 = sq[0];
  80                         iv1 = sq[2];
  81                         iv2 = sq[4];
  82                         iv3 = sq[6];
  83                         break;
  84                 }
  85                 br_enc32le(buf + 16, q[1] ^ sq[0]);
  86                 br_enc32le(buf + 20, q[3] ^ sq[2]);
  87                 br_enc32le(buf + 24, q[5] ^ sq[4]);
  88                 br_enc32le(buf + 28, q[7] ^ sq[6]);
  89                 iv0 = sq[1];
  90                 iv1 = sq[3];
  91                 iv2 = sq[5];
  92                 iv3 = sq[7];
  93                 buf += 32;
  94                 len -= 32;
  95         }
  96         br_enc32le(ivbuf, iv0);
  97         br_enc32le(ivbuf + 4, iv1);
  98         br_enc32le(ivbuf + 8, iv2);
  99         br_enc32le(ivbuf + 12, iv3);
 100 }
 101
 102 /* see bearssl_block.h */
 103 const br_block_cbcdec_class br_aes_ct_cbcdec_vtable = {
 104         sizeof(br_aes_ct_cbcdec_keys),
 105         16,
 106         4,
 107         (void (*)(const br_block_cbcdec_class **, const void *, size_t))
 108                 &br_aes_ct_cbcdec_init,
 109         (void (*)(const br_block_cbcdec_class *const *, void *, void *, size_t))
 110                 &br_aes_ct_cbcdec_run
 111 };