bn_gcd.c revision 55714
155714Skris/* crypto/bn/bn_gcd.c */ 255714Skris/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) 355714Skris * All rights reserved. 455714Skris * 555714Skris * This package is an SSL implementation written 655714Skris * by Eric Young (eay@cryptsoft.com). 755714Skris * The implementation was written so as to conform with Netscapes SSL. 855714Skris * 955714Skris * This library is free for commercial and non-commercial use as long as 1055714Skris * the following conditions are aheared to. The following conditions 1155714Skris * apply to all code found in this distribution, be it the RC4, RSA, 1255714Skris * lhash, DES, etc., code; not just the SSL code. The SSL documentation 1355714Skris * included with this distribution is covered by the same copyright terms 1455714Skris * except that the holder is Tim Hudson (tjh@cryptsoft.com). 1555714Skris * 1655714Skris * Copyright remains Eric Young's, and as such any Copyright notices in 1755714Skris * the code are not to be removed. 1855714Skris * If this package is used in a product, Eric Young should be given attribution 1955714Skris * as the author of the parts of the library used. 2055714Skris * This can be in the form of a textual message at program startup or 2155714Skris * in documentation (online or textual) provided with the package. 2255714Skris * 2355714Skris * Redistribution and use in source and binary forms, with or without 2455714Skris * modification, are permitted provided that the following conditions 2555714Skris * are met: 2655714Skris * 1. Redistributions of source code must retain the copyright 2755714Skris * notice, this list of conditions and the following disclaimer. 2855714Skris * 2. Redistributions in binary form must reproduce the above copyright 2955714Skris * notice, this list of conditions and the following disclaimer in the 3055714Skris * documentation and/or other materials provided with the distribution. 3155714Skris * 3. All advertising materials mentioning features or use of this software 3255714Skris * must display the following acknowledgement: 3355714Skris * "This product includes cryptographic software written by 3455714Skris * Eric Young (eay@cryptsoft.com)" 3555714Skris * The word 'cryptographic' can be left out if the rouines from the library 3655714Skris * being used are not cryptographic related :-). 3755714Skris * 4. If you include any Windows specific code (or a derivative thereof) from 3855714Skris * the apps directory (application code) you must include an acknowledgement: 3955714Skris * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" 4055714Skris * 4155714Skris * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND 4255714Skris * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 4355714Skris * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 4455714Skris * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 4555714Skris * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 4655714Skris * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 4755714Skris * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 4855714Skris * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 4955714Skris * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 5055714Skris * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 5155714Skris * SUCH DAMAGE. 5255714Skris * 5355714Skris * The licence and distribution terms for any publically available version or 5455714Skris * derivative of this code cannot be changed. i.e. this code cannot simply be 5555714Skris * copied and put under another distribution licence 5655714Skris * [including the GNU Public Licence.] 5755714Skris */ 5855714Skris 5955714Skris#include <stdio.h> 6055714Skris#include "cryptlib.h" 6155714Skris#include "bn_lcl.h" 6255714Skris 6355714Skrisstatic BIGNUM *euclid(BIGNUM *a, BIGNUM *b); 6455714Skrisint BN_gcd(BIGNUM *r, BIGNUM *in_a, BIGNUM *in_b, BN_CTX *ctx) 6555714Skris { 6655714Skris BIGNUM *a,*b,*t; 6755714Skris int ret=0; 6855714Skris 6955714Skris bn_check_top(in_a); 7055714Skris bn_check_top(in_b); 7155714Skris 7255714Skris a= &(ctx->bn[ctx->tos]); 7355714Skris b= &(ctx->bn[ctx->tos+1]); 7455714Skris 7555714Skris if (BN_copy(a,in_a) == NULL) goto err; 7655714Skris if (BN_copy(b,in_b) == NULL) goto err; 7755714Skris 7855714Skris if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; } 7955714Skris t=euclid(a,b); 8055714Skris if (t == NULL) goto err; 8155714Skris 8255714Skris if (BN_copy(r,t) == NULL) goto err; 8355714Skris ret=1; 8455714Skriserr: 8555714Skris return(ret); 8655714Skris } 8755714Skris 8855714Skrisstatic BIGNUM *euclid(BIGNUM *a, BIGNUM *b) 8955714Skris { 9055714Skris BIGNUM *t; 9155714Skris int shifts=0; 9255714Skris 9355714Skris bn_check_top(a); 9455714Skris bn_check_top(b); 9555714Skris 9655714Skris for (;;) 9755714Skris { 9855714Skris if (BN_is_zero(b)) 9955714Skris break; 10055714Skris 10155714Skris if (BN_is_odd(a)) 10255714Skris { 10355714Skris if (BN_is_odd(b)) 10455714Skris { 10555714Skris if (!BN_sub(a,a,b)) goto err; 10655714Skris if (!BN_rshift1(a,a)) goto err; 10755714Skris if (BN_cmp(a,b) < 0) 10855714Skris { t=a; a=b; b=t; } 10955714Skris } 11055714Skris else /* a odd - b even */ 11155714Skris { 11255714Skris if (!BN_rshift1(b,b)) goto err; 11355714Skris if (BN_cmp(a,b) < 0) 11455714Skris { t=a; a=b; b=t; } 11555714Skris } 11655714Skris } 11755714Skris else /* a is even */ 11855714Skris { 11955714Skris if (BN_is_odd(b)) 12055714Skris { 12155714Skris if (!BN_rshift1(a,a)) goto err; 12255714Skris if (BN_cmp(a,b) < 0) 12355714Skris { t=a; a=b; b=t; } 12455714Skris } 12555714Skris else /* a even - b even */ 12655714Skris { 12755714Skris if (!BN_rshift1(a,a)) goto err; 12855714Skris if (!BN_rshift1(b,b)) goto err; 12955714Skris shifts++; 13055714Skris } 13155714Skris } 13255714Skris } 13355714Skris if (shifts) 13455714Skris { 13555714Skris if (!BN_lshift(a,a,shifts)) goto err; 13655714Skris } 13755714Skris return(a); 13855714Skriserr: 13955714Skris return(NULL); 14055714Skris } 14155714Skris 14255714Skris/* solves ax == 1 (mod n) */ 14355714SkrisBIGNUM *BN_mod_inverse(BIGNUM *in, BIGNUM *a, const BIGNUM *n, BN_CTX *ctx) 14455714Skris { 14555714Skris BIGNUM *A,*B,*X,*Y,*M,*D,*R; 14655714Skris BIGNUM *T,*ret=NULL; 14755714Skris int sign; 14855714Skris 14955714Skris bn_check_top(a); 15055714Skris bn_check_top(n); 15155714Skris 15255714Skris A= &(ctx->bn[ctx->tos]); 15355714Skris B= &(ctx->bn[ctx->tos+1]); 15455714Skris X= &(ctx->bn[ctx->tos+2]); 15555714Skris D= &(ctx->bn[ctx->tos+3]); 15655714Skris M= &(ctx->bn[ctx->tos+4]); 15755714Skris Y= &(ctx->bn[ctx->tos+5]); 15855714Skris ctx->tos+=6; 15955714Skris if (in == NULL) 16055714Skris R=BN_new(); 16155714Skris else 16255714Skris R=in; 16355714Skris if (R == NULL) goto err; 16455714Skris 16555714Skris BN_zero(X); 16655714Skris BN_one(Y); 16755714Skris if (BN_copy(A,a) == NULL) goto err; 16855714Skris if (BN_copy(B,n) == NULL) goto err; 16955714Skris sign=1; 17055714Skris 17155714Skris while (!BN_is_zero(B)) 17255714Skris { 17355714Skris if (!BN_div(D,M,A,B,ctx)) goto err; 17455714Skris T=A; 17555714Skris A=B; 17655714Skris B=M; 17755714Skris /* T has a struct, M does not */ 17855714Skris 17955714Skris if (!BN_mul(T,D,X,ctx)) goto err; 18055714Skris if (!BN_add(T,T,Y)) goto err; 18155714Skris M=Y; 18255714Skris Y=X; 18355714Skris X=T; 18455714Skris sign= -sign; 18555714Skris } 18655714Skris if (sign < 0) 18755714Skris { 18855714Skris if (!BN_sub(Y,n,Y)) goto err; 18955714Skris } 19055714Skris 19155714Skris if (BN_is_one(A)) 19255714Skris { if (!BN_mod(R,Y,n,ctx)) goto err; } 19355714Skris else 19455714Skris { 19555714Skris BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE); 19655714Skris goto err; 19755714Skris } 19855714Skris ret=R; 19955714Skriserr: 20055714Skris if ((ret == NULL) && (in == NULL)) BN_free(R); 20155714Skris ctx->tos-=6; 20255714Skris return(ret); 20355714Skris } 20455714Skris 205