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/*
* Copyright (c) 2018 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 */
size_t
br_rsa_i31_compute_modulus(void *n, const br_rsa_private_key *sk)
{
uint32_t tmp[4 * (((BR_MAX_RSA_SIZE / 2) + 30) / 31) + 5];
uint32_t *t, *p, *q;
const unsigned char *pbuf, *qbuf;
size_t nlen, plen, qlen, tlen;
/*
* Compute actual byte and lengths for p and q.
*/
pbuf = sk->p;
plen = sk->plen;
while (plen > 0 && *pbuf == 0) {
pbuf ++;
plen --;
}
qbuf = sk->q;
qlen = sk->qlen;
while (qlen > 0 && *qbuf == 0) {
qbuf ++;
qlen --;
}
t = tmp;
tlen = (sizeof tmp) / (sizeof tmp[0]);
/*
* Decode p.
*/
if ((31 * tlen) < (plen << 3) + 31) {
return 0;
}
br_i31_decode(t, pbuf, plen);
p = t;
plen = (p[0] + 63) >> 5;
t += plen;
tlen -= plen;
/*
* Decode q.
*/
if ((31 * tlen) < (qlen << 3) + 31) {
return 0;
}
br_i31_decode(t, qbuf, qlen);
q = t;
qlen = (q[0] + 63) >> 5;
t += qlen;
tlen -= qlen;
/*
* Computation can proceed only if we have enough room for the
* modulus.
*/
if (tlen < (plen + qlen + 1)) {
return 0;
}
/*
* Private key already contains the modulus bit length, from which
* we can infer the output length. Even if n is NULL, we still had
* to decode p and q to make sure that the product can be computed.
*/
nlen = (sk->n_bitlen + 7) >> 3;
if (n != NULL) {
br_i31_zero(t, p[0]);
br_i31_mulacc(t, p, q);
br_i31_encode(n, nlen, t);
}
return nlen;
}
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