_ Git - BearSSL/blob - src/rsa/rsa_ssl_decrypt.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_rsa.h */
  28 uint32_t
  29 br_rsa_ssl_decrypt(br_rsa_private core, const br_rsa_private_key *sk,
  30         unsigned char *data, size_t len)
  31 {
  32         uint32_t x;
  33         size_t u;
  34
  35         /*
  36          * A first check on length. Since this test works only on the
  37          * buffer length, it needs not (and cannot) be constant-time.
  38          */
  39         if (len < 59 || len != (sk->n_bitlen + 7) >> 3) {
  40                 return 0;
  41         }
  42         x = core(data, sk);
  43
  44         x &= EQ(data[0], 0x00);
  45         x &= EQ(data[1], 0x02);
  46         for (u = 2; u < (len - 49); u ++) {
  47                 x &= NEQ(data[u], 0);
  48         }
  49         x &= EQ(data[len - 49], 0x00);
  50         memmove(data, data + len - 48, 48);
  51         return x;
  52 }