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#if BR_INT128 || BR_UMUL128
28
29/*
30 * As a strict minimum, we need four buffers that can hold a
31 * modular integer. But TLEN is expressed in 64-bit words.
32 */
33#define TLEN   (2 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31)))
34
35/* see bearssl_rsa.h */
36uint32_t
37br_rsa_i62_public(unsigned char *x, size_t xlen,
38	const br_rsa_public_key *pk)
39{
40	const unsigned char *n;
41	size_t nlen;
42	uint64_t tmp[TLEN];
43	uint32_t *m, *a;
44	size_t fwlen;
45	long z;
46	uint32_t m0i, r;
47
48	/*
49	 * Get the actual length of the modulus, and see if it fits within
50	 * our stack buffer. We also check that the length of x[] is valid.
51	 */
52	n = pk->n;
53	nlen = pk->nlen;
54	while (nlen > 0 && *n == 0) {
55		n ++;
56		nlen --;
57	}
58	if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
59		return 0;
60	}
61	z = (long)nlen << 3;
62	fwlen = 1;
63	while (z > 0) {
64		z -= 31;
65		fwlen ++;
66	}
67	/*
68	 * Convert fwlen to a count in 62-bit words.
69	 */
70	fwlen = (fwlen + 1) >> 1;
71
72	/*
73	 * The modulus gets decoded into m[].
74	 * The value to exponentiate goes into a[].
75	 */
76	m = (uint32_t *)tmp;
77	a = (uint32_t *)(tmp + fwlen);
78
79	/*
80	 * Decode the modulus.
81	 */
82	br_i31_decode(m, n, nlen);
83	m0i = br_i31_ninv31(m[1]);
84
85	/*
86	 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
87	 * an odd integer.
88	 */
89	r = m0i & 1;
90
91	/*
92	 * Decode x[] into a[]; we also check that its value is proper.
93	 */
94	r &= br_i31_decode_mod(a, x, xlen, m);
95
96	/*
97	 * Compute the modular exponentiation.
98	 */
99	br_i62_modpow_opt(a, pk->e, pk->elen, m, m0i,
100		tmp + 2 * fwlen, TLEN - 2 * fwlen);
101
102	/*
103	 * Encode the result.
104	 */
105	br_i31_encode(x, xlen, a);
106	return r;
107}
108
109/* see bearssl_rsa.h */
110br_rsa_public
111br_rsa_i62_public_get(void)
112{
113	return &br_rsa_i62_public;
114}
115
116#else
117
118/* see bearssl_rsa.h */
119br_rsa_public
120br_rsa_i62_public_get(void)
121{
122	return 0;
123}
124
125#endif
126