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 */
28 uint32_t
29 br_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