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/*
* Copyright (c) 2016 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"
/* see bearssl_rsa.h */
uint32_t
br_rsa_i32_public(unsigned char *x, size_t xlen,
const br_rsa_public_key *pk)
{
const unsigned char *n;
size_t nlen;
uint32_t m[1 + (BR_MAX_RSA_SIZE >> 5)];
uint32_t a[1 + (BR_MAX_RSA_SIZE >> 5)];
uint32_t t1[1 + (BR_MAX_RSA_SIZE >> 5)];
uint32_t t2[1 + (BR_MAX_RSA_SIZE >> 5)];
uint32_t m0i, 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;
}
br_i32_decode(m, n, nlen);
m0i = br_i32_ninv32(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_i32_decode_mod(a, x, xlen, m);
/*
* Compute the modular exponentiation.
*/
br_i32_modpow(a, pk->e, pk->elen, m, m0i, t1, t2);
/*
* Encode the result.
*/
br_i32_encode(x, xlen, a);
return r;
}
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