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/*
* Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/*
* As a strict minimum, we need four buffers that can hold a
* modular integer.
*/
#define TLEN (4 * (2 + ((BR_MAX_RSA_SIZE + 14) / 15)))
/* see bearssl_rsa.h */
uint32_t
br_rsa_i15_public(unsigned char *x, size_t xlen,
const br_rsa_public_key *pk)
{
const unsigned char *n;
size_t nlen;
uint16_t tmp[1 + TLEN];
uint16_t *m, *a, *t;
size_t fwlen;
long z;
uint16_t m0i;
uint32_t r;
/*
* Get the actual length of the modulus, and see if it fits within
* our stack buffer. We also check that the length of x[] is valid.
*/
n = pk->n;
nlen = pk->nlen;
while (nlen > 0 && *n == 0) {
n ++;
nlen --;
}
if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
return 0;
}
z = (long)nlen << 3;
fwlen = 1;
while (z > 0) {
z -= 15;
fwlen ++;
}
/*
* Round up length to an even number.
*/
fwlen += (fwlen & 1);
/*
* The modulus gets decoded into m[].
* The value to exponentiate goes into a[].
* The temporaries for modular exponentiations are in t[].
*
* We want the first value word of each integer to be aligned
* on a 32-bit boundary.
*/
m = tmp;
if (((uintptr_t)m & 2) == 0) {
m ++;
}
a = m + fwlen;
t = m + 2 * fwlen;
/*
* Decode the modulus.
*/
br_i15_decode(m, n, nlen);
m0i = br_i15_ninv15(m[1]);
/*
* Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
* an odd integer.
*/
r = m0i & 1;
/*
* Decode x[] into a[]; we also check that its value is proper.
*/
r &= br_i15_decode_mod(a, x, xlen, m);
/*
* Compute the modular exponentiation.
*/
br_i15_modpow_opt(a, pk->e, pk->elen, m, m0i, t, TLEN - 2 * fwlen);
/*
* Encode the result.
*/
br_i15_encode(x, xlen, a);
return r;
}
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