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src/rsa/rsa_i15_priv.c  view on Meta::CPAN

/*
 * 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"

#define U      (2 + ((BR_MAX_RSA_FACTOR + 14) / 15))
#define TLEN   (8 * U)

/* see bearssl_rsa.h */
uint32_t
br_rsa_i15_private(unsigned char *x, const br_rsa_private_key *sk)
{
	const unsigned char *p, *q;
	size_t plen, qlen;
	size_t fwlen;
	uint16_t p0i, q0i;
	size_t xlen, u;
	uint16_t tmp[1 + TLEN];
	long z;
	uint16_t *mp, *mq, *s1, *s2, *t1, *t2, *t3;
	uint32_t r;

	/*
	 * Compute the actual lengths of p and q, in bytes.
	 * These lengths are not considered secret (we cannot really hide
	 * them anyway in constant-time code).
	 */
	p = sk->p;
	plen = sk->plen;
	while (plen > 0 && *p == 0) {
		p ++;
		plen --;
	}
	q = sk->q;
	qlen = sk->qlen;
	while (qlen > 0 && *q == 0) {
		q ++;
		qlen --;
	}

	/*
	 * Compute the maximum factor length, in words.
	 */
	z = (long)(plen > qlen ? plen : qlen) << 3;
	fwlen = 1;
	while (z > 0) {
		z -= 15;
		fwlen ++;
	}
	/*
	 * Round up the word length to an even number.
	 */
	fwlen += (fwlen & 1);

	/*
	 * We need to fit at least 6 values in the stack buffer.
	 */
	if (6 * fwlen > TLEN) {
		return 0;
	}

	/*
	 * Compute signature length (in bytes).
	 */
	xlen = (sk->n_bitlen + 7) >> 3;

	/*
	 * Ensure 32-bit alignment for value words.
	 */
	mq = tmp;
	if (((uintptr_t)mq & 2) == 0) {