1*0957b409SSimon J. Gerraty /*
2*0957b409SSimon J. Gerraty * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3*0957b409SSimon J. Gerraty *
4*0957b409SSimon J. Gerraty * Permission is hereby granted, free of charge, to any person obtaining
5*0957b409SSimon J. Gerraty * a copy of this software and associated documentation files (the
6*0957b409SSimon J. Gerraty * "Software"), to deal in the Software without restriction, including
7*0957b409SSimon J. Gerraty * without limitation the rights to use, copy, modify, merge, publish,
8*0957b409SSimon J. Gerraty * distribute, sublicense, and/or sell copies of the Software, and to
9*0957b409SSimon J. Gerraty * permit persons to whom the Software is furnished to do so, subject to
10*0957b409SSimon J. Gerraty * the following conditions:
11*0957b409SSimon J. Gerraty *
12*0957b409SSimon J. Gerraty * The above copyright notice and this permission notice shall be
13*0957b409SSimon J. Gerraty * included in all copies or substantial portions of the Software.
14*0957b409SSimon J. Gerraty *
15*0957b409SSimon J. Gerraty * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16*0957b409SSimon J. Gerraty * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17*0957b409SSimon J. Gerraty * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18*0957b409SSimon J. Gerraty * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19*0957b409SSimon J. Gerraty * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20*0957b409SSimon J. Gerraty * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21*0957b409SSimon J. Gerraty * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22*0957b409SSimon J. Gerraty * SOFTWARE.
23*0957b409SSimon J. Gerraty */
24*0957b409SSimon J. Gerraty
25*0957b409SSimon J. Gerraty #include "inner.h"
26*0957b409SSimon J. Gerraty
27*0957b409SSimon J. Gerraty /*
28*0957b409SSimon J. Gerraty * As a strict minimum, we need four buffers that can hold a
29*0957b409SSimon J. Gerraty * modular integer.
30*0957b409SSimon J. Gerraty */
31*0957b409SSimon J. Gerraty #define TLEN (4 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31)))
32*0957b409SSimon J. Gerraty
33*0957b409SSimon J. Gerraty /* see bearssl_rsa.h */
34*0957b409SSimon J. Gerraty uint32_t
br_rsa_i31_public(unsigned char * x,size_t xlen,const br_rsa_public_key * pk)35*0957b409SSimon J. Gerraty br_rsa_i31_public(unsigned char *x, size_t xlen,
36*0957b409SSimon J. Gerraty const br_rsa_public_key *pk)
37*0957b409SSimon J. Gerraty {
38*0957b409SSimon J. Gerraty const unsigned char *n;
39*0957b409SSimon J. Gerraty size_t nlen;
40*0957b409SSimon J. Gerraty uint32_t tmp[1 + TLEN];
41*0957b409SSimon J. Gerraty uint32_t *m, *a, *t;
42*0957b409SSimon J. Gerraty size_t fwlen;
43*0957b409SSimon J. Gerraty long z;
44*0957b409SSimon J. Gerraty uint32_t m0i, r;
45*0957b409SSimon J. Gerraty
46*0957b409SSimon J. Gerraty /*
47*0957b409SSimon J. Gerraty * Get the actual length of the modulus, and see if it fits within
48*0957b409SSimon J. Gerraty * our stack buffer. We also check that the length of x[] is valid.
49*0957b409SSimon J. Gerraty */
50*0957b409SSimon J. Gerraty n = pk->n;
51*0957b409SSimon J. Gerraty nlen = pk->nlen;
52*0957b409SSimon J. Gerraty while (nlen > 0 && *n == 0) {
53*0957b409SSimon J. Gerraty n ++;
54*0957b409SSimon J. Gerraty nlen --;
55*0957b409SSimon J. Gerraty }
56*0957b409SSimon J. Gerraty if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
57*0957b409SSimon J. Gerraty return 0;
58*0957b409SSimon J. Gerraty }
59*0957b409SSimon J. Gerraty z = (long)nlen << 3;
60*0957b409SSimon J. Gerraty fwlen = 1;
61*0957b409SSimon J. Gerraty while (z > 0) {
62*0957b409SSimon J. Gerraty z -= 31;
63*0957b409SSimon J. Gerraty fwlen ++;
64*0957b409SSimon J. Gerraty }
65*0957b409SSimon J. Gerraty /*
66*0957b409SSimon J. Gerraty * Round up length to an even number.
67*0957b409SSimon J. Gerraty */
68*0957b409SSimon J. Gerraty fwlen += (fwlen & 1);
69*0957b409SSimon J. Gerraty
70*0957b409SSimon J. Gerraty /*
71*0957b409SSimon J. Gerraty * The modulus gets decoded into m[].
72*0957b409SSimon J. Gerraty * The value to exponentiate goes into a[].
73*0957b409SSimon J. Gerraty * The temporaries for modular exponentiation are in t[].
74*0957b409SSimon J. Gerraty */
75*0957b409SSimon J. Gerraty m = tmp;
76*0957b409SSimon J. Gerraty a = m + fwlen;
77*0957b409SSimon J. Gerraty t = m + 2 * fwlen;
78*0957b409SSimon J. Gerraty
79*0957b409SSimon J. Gerraty /*
80*0957b409SSimon J. Gerraty * Decode the modulus.
81*0957b409SSimon J. Gerraty */
82*0957b409SSimon J. Gerraty br_i31_decode(m, n, nlen);
83*0957b409SSimon J. Gerraty m0i = br_i31_ninv31(m[1]);
84*0957b409SSimon J. Gerraty
85*0957b409SSimon J. Gerraty /*
86*0957b409SSimon J. Gerraty * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
87*0957b409SSimon J. Gerraty * an odd integer.
88*0957b409SSimon J. Gerraty */
89*0957b409SSimon J. Gerraty r = m0i & 1;
90*0957b409SSimon J. Gerraty
91*0957b409SSimon J. Gerraty /*
92*0957b409SSimon J. Gerraty * Decode x[] into a[]; we also check that its value is proper.
93*0957b409SSimon J. Gerraty */
94*0957b409SSimon J. Gerraty r &= br_i31_decode_mod(a, x, xlen, m);
95*0957b409SSimon J. Gerraty
96*0957b409SSimon J. Gerraty /*
97*0957b409SSimon J. Gerraty * Compute the modular exponentiation.
98*0957b409SSimon J. Gerraty */
99*0957b409SSimon J. Gerraty br_i31_modpow_opt(a, pk->e, pk->elen, m, m0i, t, TLEN - 2 * fwlen);
100*0957b409SSimon J. Gerraty
101*0957b409SSimon J. Gerraty /*
102*0957b409SSimon J. Gerraty * Encode the result.
103*0957b409SSimon J. Gerraty */
104*0957b409SSimon J. Gerraty br_i31_encode(x, xlen, a);
105*0957b409SSimon J. Gerraty return r;
106*0957b409SSimon J. Gerraty }
107