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 */
36 uint32_t
br_rsa_i62_public(unsigned char * x,size_t xlen,const br_rsa_public_key * pk)37 br_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 */
110 br_rsa_public
br_rsa_i62_public_get(void)111 br_rsa_i62_public_get(void)
112 {
113 return &br_rsa_i62_public;
114 }
115
116 #else
117
118 /* see bearssl_rsa.h */
119 br_rsa_public
br_rsa_i62_public_get(void)120 br_rsa_i62_public_get(void)
121 {
122 return 0;
123 }
124
125 #endif
126