Fixed typo in C preprocessor expression.
[BearSSL] / src / rsa / rsa_i32_priv.c
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 #define U (1 + (BR_MAX_RSA_FACTOR >> 5))
28
29 /* see bearssl_rsa.h */
30 uint32_t
31 br_rsa_i32_private(unsigned char *x, const br_rsa_private_key *sk)
32 {
33 const unsigned char *p, *q;
34 size_t plen, qlen;
35 uint32_t tmp[6 * U];
36 uint32_t *mp, *mq, *s1, *s2, *t1, *t2, *t3;
37 uint32_t p0i, q0i;
38 size_t xlen;
39
40 /*
41 * All our temporary buffers are from the tmp[] array.
42 *
43 * The mp, mq, s1, s2, t1 and t2 buffers are large enough to
44 * contain a RSA factor. The t3 buffer can contain a complete
45 * RSA modulus. t3 shares its storage space with s2, s1 and t1,
46 * in that order (this is important, see below).
47 */
48 mq = tmp;
49 mp = tmp + U;
50 t2 = tmp + 2 * U;
51 s2 = tmp + 3 * U;
52 s1 = tmp + 4 * U;
53 t1 = tmp + 5 * U;
54 t3 = s2;
55
56 /*
57 * Compute the actual lengths (in bytes) of p and q, and check
58 * that they fit within our stack buffers.
59 */
60 p = sk->p;
61 plen = sk->plen;
62 while (plen > 0 && *p == 0) {
63 p ++;
64 plen --;
65 }
66 q = sk->q;
67 qlen = sk->qlen;
68 while (qlen > 0 && *q == 0) {
69 q ++;
70 qlen --;
71 }
72 if (plen > (BR_MAX_RSA_FACTOR >> 3)
73 || qlen > (BR_MAX_RSA_FACTOR >> 3))
74 {
75 return 0;
76 }
77
78 /*
79 * Decode p and q.
80 */
81 br_i32_decode(mp, p, plen);
82 br_i32_decode(mq, q, qlen);
83
84 /*
85 * obsolete -- we do not compute the length of n, it is now
86 * an input parameter.
87 br_i32_zero(t3, mp[0]);
88 br_i32_mulacc(t3, mp, mq);
89 n_bitlen = br_i32_bit_length(t3 + 1, (t3[0] + 31) >> 5);
90 if (xlen != ((n_bitlen + 7) >> 3)) {
91 return 0;
92 }
93 */
94 xlen = (sk->n_bitlen + 7) >> 3;
95
96 /*
97 * Compute s1 = x^dp mod p.
98 */
99 p0i = br_i32_ninv32(mp[1]);
100 br_i32_decode_reduce(s1, x, xlen, mp);
101 br_i32_modpow(s1, sk->dp, sk->dplen, mp, p0i, t1, t2);
102
103 /*
104 * Compute s2 = x^dq mod q.
105 */
106 q0i = br_i32_ninv32(mq[1]);
107 br_i32_decode_reduce(s2, x, xlen, mq);
108 br_i32_modpow(s2, sk->dq, sk->dqlen, mq, q0i, t1, t2);
109
110 /*
111 * Compute:
112 * h = (s1 - s2)*(1/q) mod p
113 * s1 is an integer modulo p, but s2 is modulo q. PKCS#1 is
114 * unclear about whether p may be lower than q (some existing,
115 * widely deployed implementations of RSA don't tolerate p < q),
116 * but we want to support that occurrence, so we need to use the
117 * reduction function.
118 *
119 * Since we use br_i32_decode_reduce() for iq (purportedly, the
120 * inverse of q modulo p), we also tolerate improperly large
121 * values for this parameter.
122 */
123 br_i32_reduce(t2, s2, mp);
124 br_i32_add(s1, mp, br_i32_sub(s1, t2, 1));
125 br_i32_to_monty(s1, mp);
126 br_i32_decode_reduce(t1, sk->iq, sk->iqlen, mp);
127 br_i32_montymul(t2, s1, t1, mp, p0i);
128
129 /*
130 * h is now in t2. We compute the final result:
131 * s = s2 + q*h
132 * All these operations are non-modular.
133 *
134 * We need mq, s2 and t2. We use the t3 buffer as destination.
135 * The buffers mp, s1 and t1 are no longer needed. Moreover,
136 * the first step is to copy s2 into the destination buffer t3.
137 * We thus arranged for t3 to actually share space with s2, and
138 * to be followed by the space formerly used by s1 and t1.
139 */
140 br_i32_mulacc(t3, mq, t2);
141
142 /*
143 * Encode the result. Since we already checked the value of xlen,
144 * we can just use it right away.
145 */
146 br_i32_encode(x, xlen, t3);
147
148 /*
149 * The only error conditions remaining at that point are invalid
150 * values for p and q (even integers).
151 */
152 return p0i & q0i & 1;
153 }