100 lines
2.5 KiB
C
100 lines
2.5 KiB
C
/*
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* Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "inner.h"
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/* see bearssl_rsa.h */
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size_t
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br_rsa_i15_compute_modulus(void *n, const br_rsa_private_key *sk)
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{
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uint16_t tmp[2 * ((BR_MAX_RSA_SIZE + 14) / 15) + 5];
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uint16_t *t, *p, *q;
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const unsigned char *pbuf, *qbuf;
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size_t nlen, plen, qlen, tlen;
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/*
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* Compute actual byte and lengths for p and q.
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*/
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pbuf = sk->p;
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plen = sk->plen;
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while (plen > 0 && *pbuf == 0) {
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pbuf ++;
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plen --;
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}
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qbuf = sk->q;
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qlen = sk->qlen;
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while (qlen > 0 && *qbuf == 0) {
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qbuf ++;
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qlen --;
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}
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t = tmp;
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tlen = (sizeof tmp) / (sizeof tmp[0]);
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/*
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* Decode p.
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*/
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if ((15 * tlen) < (plen << 3) + 15) {
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return 0;
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}
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br_i15_decode(t, pbuf, plen);
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p = t;
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plen = (p[0] + 31) >> 4;
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t += plen;
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tlen -= plen;
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/*
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* Decode q.
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*/
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if ((15 * tlen) < (qlen << 3) + 15) {
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return 0;
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}
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br_i15_decode(t, qbuf, qlen);
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q = t;
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qlen = (q[0] + 31) >> 4;
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t += qlen;
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tlen -= qlen;
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/*
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* Computation can proceed only if we have enough room for the
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* modulus.
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*/
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if (tlen < (plen + qlen + 1)) {
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return 0;
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}
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/*
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* Private key already contains the modulus bit length, from which
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* we can infer the output length. Even if n is NULL, we still had
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* to decode p and q to make sure that the product can be computed.
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*/
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nlen = (sk->n_bitlen + 7) >> 3;
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if (n != NULL) {
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br_i15_zero(t, p[0]);
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br_i15_mulacc(t, p, q);
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br_i15_encode(n, nlen, t);
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}
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return nlen;
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}
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