2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
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
28 * As a strict minimum, we need four buffers that can hold a
31 #define TLEN (4 * (2 + ((BR_MAX_RSA_SIZE + 14) / 15)))
33 /* see bearssl_rsa.h */
35 br_rsa_i15_public(unsigned char *x
, size_t xlen
,
36 const br_rsa_public_key
*pk
)
38 const unsigned char *n
;
40 uint16_t tmp
[1 + TLEN
];
48 * Get the actual length of the modulus, and see if it fits within
49 * our stack buffer. We also check that the length of x[] is valid.
53 while (nlen
> 0 && *n
== 0) {
57 if (nlen
== 0 || nlen
> (BR_MAX_RSA_SIZE
>> 3) || xlen
!= nlen
) {
67 * Round up length to an even number.
72 * The modulus gets decoded into m[].
73 * The value to exponentiate goes into a[].
74 * The temporaries for modular exponentiations are in t[].
76 * We want the first value word of each integer to be aligned
77 * on a 32-bit boundary.
80 if (((uintptr_t)m
& 2) == 0) {
89 br_i15_decode(m
, n
, nlen
);
90 m0i
= br_i15_ninv15(m
[1]);
93 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
99 * Decode x[] into a[]; we also check that its value is proper.
101 r
&= br_i15_decode_mod(a
, x
, xlen
, m
);
104 * Compute the modular exponentiation.
106 br_i15_modpow_opt(a
, pk
->e
, pk
->elen
, m
, m0i
, t
, TLEN
- 2 * fwlen
);
111 br_i15_encode(x
, xlen
, a
);