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  }