1/*
2 * Copyright (c) 2017 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 inner.h */
28uint32_t
29br_rsa_pkcs1_sig_pad(const unsigned char *hash_oid,
30	const unsigned char *hash, size_t hash_len,
31	uint32_t n_bitlen, unsigned char *x)
32{
33	size_t u, x3, xlen;
34
35	/*
36	 * Padded hash value has format:
37	 *  00 01 FF .. FF 00 30 x1 30 x2 06 x3 OID 05 00 04 x4 HASH
38	 *
39	 * with the following rules:
40	 *
41	 *  -- Total length is equal to the modulus length (unsigned
42	 *     encoding).
43	 *
44	 *  -- There must be at least eight bytes of value 0xFF.
45	 *
46	 *  -- x4 is equal to the hash length (hash_len).
47	 *
48	 *  -- x3 is equal to the encoded OID value length (hash_oid[0]).
49	 *
50	 *  -- x2 = x3 + 4.
51	 *
52	 *  -- x1 = x2 + x4 + 4 = x3 + x4 + 8.
53	 *
54	 * Note: the "05 00" is optional (signatures with and without
55	 * that sequence exist in practice), but notes in PKCS#1 seem to
56	 * indicate that the presence of that sequence (specifically,
57	 * an ASN.1 NULL value for the hash parameters) may be slightly
58	 * more "standard" than the opposite.
59	 */
60	xlen = (n_bitlen + 7) >> 3;
61
62	if (hash_oid == NULL) {
63		if (xlen < hash_len + 11) {
64			return 0;
65		}
66		x[0] = 0x00;
67		x[1] = 0x01;
68		u = xlen - hash_len;
69		memset(x + 2, 0xFF, u - 3);
70		x[u - 1] = 0x00;
71	} else {
72		x3 = hash_oid[0];
73
74		/*
75		 * Check that there is enough room for all the elements,
76		 * including at least eight bytes of value 0xFF.
77		 */
78		if (xlen < (x3 + hash_len + 21)) {
79			return 0;
80		}
81		x[0] = 0x00;
82		x[1] = 0x01;
83		u = xlen - x3 - hash_len - 11;
84		memset(x + 2, 0xFF, u - 2);
85		x[u] = 0x00;
86		x[u + 1] = 0x30;
87		x[u + 2] = x3 + hash_len + 8;
88		x[u + 3] = 0x30;
89		x[u + 4] = x3 + 4;
90		x[u + 5] = 0x06;
91		memcpy(x + u + 6, hash_oid, x3 + 1);
92		u += x3 + 7;
93		x[u ++] = 0x05;
94		x[u ++] = 0x00;
95		x[u ++] = 0x04;
96		x[u ++] = hash_len;
97	}
98	memcpy(x + u, hash, hash_len);
99	return 1;
100}
101