bn_recp.c

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/* crypto/bn/bn_recp.c */
/* Copyright (C) 1995-1998 Eric Young ([e-mail])
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young ([e-mail]).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson ([e-mail]).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young ([e-mail])"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson ([e-mail])"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include "cryptlib.h"
#include "bn_lcl.h"
#include "workaround.h"

void BN_RECP_CTX_init(BN_RECP_CTX * recp)
{
    BN_init(&(recp->N));
    BN_init(&(recp->Nr));
    recp->num_bits = 0;
    recp->flags = 0;
}

BN_RECP_CTX *BN_RECP_CTX_new(void)
{
    BN_RECP_CTX *ret;

    if ((ret = (BN_RECP_CTX *) Our_malloc(sizeof(BN_RECP_CTX))) == NULL)
	return (NULL);

    BN_RECP_CTX_init(ret);
    ret->flags = BN_FLG_MALLOCED;
    return (ret);
}

void BN_RECP_CTX_free(BN_RECP_CTX * recp)
{
    if (recp == NULL)
	return;

    BN_free(&(recp->N));
    BN_free(&(recp->Nr));
    if (recp->flags & BN_FLG_MALLOCED)
	OPENSSL_free(recp);
}

int BN_RECP_CTX_set(BN_RECP_CTX * recp, const BIGNUM * d, BN_CTX * ctx)
{
    BN_copy(&(recp->N), d);
    BN_zero(&(recp->Nr));
    recp->num_bits = BN_num_bits(d);
    recp->shift = 0;
    return (1);
}

int BN_mod_mul_reciprocal(BIGNUM * r, BIGNUM * x, BIGNUM * y,
			  BN_RECP_CTX * recp, BN_CTX * ctx)
{
    int ret = 0;
    BIGNUM *a;

    BN_CTX_start(ctx);
    if ((a = BN_CTX_get(ctx)) == NULL)
	goto err;
    if (y != NULL) {
	if (x == y) {
	    if (!BN_sqr(a, x, ctx))
		goto err;
	} else {
	    if (!BN_mul(a, x, y, ctx))
		goto err;
	}
    } else
	a = x;			/* Just do the mod */

    BN_div_recp(NULL, r, a, recp, ctx);
    ret = 1;
  err:
    BN_CTX_end(ctx);
    return (ret);
}

int BN_div_recp(BIGNUM * dv, BIGNUM * rem, BIGNUM * m, BN_RECP_CTX * recp,
		BN_CTX * ctx)
{
    int i, j, ret = 0;
    BIGNUM *a, *b, *d, *r;

    BN_CTX_start(ctx);
    a = BN_CTX_get(ctx);
    b = BN_CTX_get(ctx);
    if (dv != NULL)
	d = dv;
    else
	d = BN_CTX_get(ctx);
    if (rem != NULL)
	r = rem;
    else
	r = BN_CTX_get(ctx);
    if (a == NULL || b == NULL || d == NULL || r == NULL)
	goto err;

    if (BN_ucmp(m, &(recp->N)) < 0) {
	BN_zero(d);
	BN_copy(r, m);
	BN_CTX_end(ctx);
	return (1);
    }

    /* We want the remainder
     * Given input of ABCDEF / ab
     * we need multiply ABCDEF by 3 digests of the reciprocal of ab
     *
     */
    i = BN_num_bits(m);

    j = recp->num_bits << 1;
    if (j > i)
	i = j;
    j >>= 1;

    if (i != recp->shift)
	recp->shift = BN_reciprocal(&(recp->Nr), &(recp->N), i, ctx);

    if (!BN_rshift(a, m, j))
	goto err;
    if (!BN_mul(b, a, &(recp->Nr), ctx))
	goto err;
    if (!BN_rshift(d, b, i - j))
	goto err;
    d->neg = 0;
    if (!BN_mul(b, &(recp->N), d, ctx))
	goto err;
    if (!BN_usub(r, m, b))
	goto err;
    r->neg = 0;

#if 1
    j = 0;
    while (BN_ucmp(r, &(recp->N)) >= 0) {
	if (j++ > 2) {
	    BNerr(BN_F_BN_MOD_MUL_RECIPROCAL, BN_R_BAD_RECIPROCAL);
	    goto err;
	}
	if (!BN_usub(r, r, &(recp->N)))
	    goto err;
	if (!BN_add_word(d, 1))
	    goto err;
    }
#endif

    r->neg = BN_is_zero(r) ? 0 : m->neg;
    d->neg = m->neg ^ recp->N.neg;
    ret = 1;
  err:
    BN_CTX_end(ctx);
    return (ret);
}

/* len is the expected size of the result
 * We actually calculate with an extra word of precision, so
 * we can do faster division if the remainder is not required.
 */
int BN_reciprocal(BIGNUM * r, BIGNUM * m, int len, BN_CTX * ctx)
{
    int ret = -1;
    BIGNUM t;

    BN_init(&t);

    BN_zero(&t);
    if (!BN_set_bit(&t, len))
	goto err;

    if (!BN_div(r, NULL, &t, m, ctx))
	goto err;
    ret = len;
  err:
    BN_free(&t);
    return (ret);
}