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 */
28 uint32_t
br_rsa_i32_public(unsigned char * x,size_t xlen,const br_rsa_public_key * pk)29 br_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