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 */
28uint32_t
29br_rsa_i32_public(unsigned char *x, size_t xlen,
30	const br_rsa_public_key *pk)
31{
32	const unsigned char *n;
33	size_t nlen;
34	uint32_t m[1 + (BR_MAX_RSA_SIZE >> 5)];
35	uint32_t a[1 + (BR_MAX_RSA_SIZE >> 5)];
36	uint32_t t1[1 + (BR_MAX_RSA_SIZE >> 5)];
37	uint32_t t2[1 + (BR_MAX_RSA_SIZE >> 5)];
38	uint32_t m0i, r;
39
40	/*
41	 * Get the actual length of the modulus, and see if it fits within
42	 * our stack buffer. We also check that the length of x[] is valid.
43	 */
44	n = pk->n;
45	nlen = pk->nlen;
46	while (nlen > 0 && *n == 0) {
47		n ++;
48		nlen --;
49	}
50	if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
51		return 0;
52	}
53	br_i32_decode(m, n, nlen);
54	m0i = br_i32_ninv32(m[1]);
55
56	/*
57	 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
58	 * an odd integer.
59	 */
60	r = m0i & 1;
61
62	/*
63	 * Decode x[] into a[]; we also check that its value is proper.
64	 */
65	r &= br_i32_decode_mod(a, x, xlen, m);
66
67	/*
68	 * Compute the modular exponentiation.
69	 */
70	br_i32_modpow(a, pk->e, pk->elen, m, m0i, t1, t2);
71
72	/*
73	 * Encode the result.
74	 */
75	br_i32_encode(x, xlen, a);
76	return r;
77}
78