bn_gcd.c revision e915367e40b579d18ac13c9c58c15fec614d9890
#include "../rename.h"
/* crypto/bn/bn_gcd.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
* All rights reserved.
*
* This package is an SSL implementation written
* by Eric Young (eay@cryptsoft.com).
* 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 (tjh@cryptsoft.com).
*
* 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 (eay@cryptsoft.com)"
* 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 (tjh@cryptsoft.com)"
*
* 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"
static BIGNUM *euclid(BIGNUM *a, BIGNUM *b);
int BN_gcd(BIGNUM *r, BIGNUM *in_a, BIGNUM *in_b, BN_CTX *ctx)
{
BIGNUM *a,*b,*t;
int ret=0;
bn_check_top(in_a);
bn_check_top(in_b);
BN_CTX_start(ctx);
a = BN_CTX_get(ctx);
b = BN_CTX_get(ctx);
if (a == NULL || b == NULL) goto err;
if (BN_copy(a,in_a) == NULL) goto err;
if (BN_copy(b,in_b) == NULL) goto err;
if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; }
t=euclid(a,b);
if (t == NULL) goto err;
if (BN_copy(r,t) == NULL) goto err;
ret=1;
err:
BN_CTX_end(ctx);
return(ret);
}
static BIGNUM *euclid(BIGNUM *a, BIGNUM *b)
{
BIGNUM *t;
int shifts=0;
bn_check_top(a);
bn_check_top(b);
for (;;)
{
if (BN_is_zero(b))
break;
if (BN_is_odd(a))
{
if (BN_is_odd(b))
{
if (!BN_sub(a,a,b)) goto err;
if (!BN_rshift1(a,a)) goto err;
if (BN_cmp(a,b) < 0)
{ t=a; a=b; b=t; }
}
else /* a odd - b even */
{
if (!BN_rshift1(b,b)) goto err;
if (BN_cmp(a,b) < 0)
{ t=a; a=b; b=t; }
}
}
else /* a is even */
{
if (BN_is_odd(b))
{
if (!BN_rshift1(a,a)) goto err;
if (BN_cmp(a,b) < 0)
{ t=a; a=b; b=t; }
}
else /* a even - b even */
{
if (!BN_rshift1(a,a)) goto err;
if (!BN_rshift1(b,b)) goto err;
shifts++;
}
}
}
if (shifts)
{
if (!BN_lshift(a,a,shifts)) goto err;
}
return(a);
err:
return(NULL);
}
/* solves ax == 1 (mod n) */
BIGNUM *BN_mod_inverse(BIGNUM *in, BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
{
BIGNUM *A,*B,*X,*Y,*M,*D,*R=NULL;
BIGNUM *T,*ret=NULL;
int sign;
bn_check_top(a);
bn_check_top(n);
BN_CTX_start(ctx);
A = BN_CTX_get(ctx);
B = BN_CTX_get(ctx);
X = BN_CTX_get(ctx);
D = BN_CTX_get(ctx);
M = BN_CTX_get(ctx);
Y = BN_CTX_get(ctx);
if (Y == NULL) goto err;
if (in == NULL)
R=BN_new();
else
R=in;
if (R == NULL) goto err;
BN_zero(X);
BN_one(Y);
if (BN_copy(A,a) == NULL) goto err;
if (BN_copy(B,n) == NULL) goto err;
sign=1;
while (!BN_is_zero(B))
{
if (!BN_div(D,M,A,B,ctx)) goto err;
T=A;
A=B;
B=M;
/* T has a struct, M does not */
if (!BN_mul(T,D,X,ctx)) goto err;
if (!BN_add(T,T,Y)) goto err;
M=Y;
Y=X;
X=T;
sign= -sign;
}
if (sign < 0)
{
if (!BN_sub(Y,n,Y)) goto err;
}
if (BN_is_one(A))
{ if (!BN_mod(R,Y,n,ctx)) goto err; }
else
{
BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE);
goto err;
}
ret=R;
err:
if ((ret == NULL) && (in == NULL)) BN_free(R);
BN_CTX_end(ctx);
return(ret);
}