bn_gcd.c revision 100936
1/* crypto/bn/bn_gcd.c */ 2/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) 3 * All rights reserved. 4 * 5 * This package is an SSL implementation written 6 * by Eric Young (eay@cryptsoft.com). 7 * The implementation was written so as to conform with Netscapes SSL. 8 * 9 * This library is free for commercial and non-commercial use as long as 10 * the following conditions are aheared to. The following conditions 11 * apply to all code found in this distribution, be it the RC4, RSA, 12 * lhash, DES, etc., code; not just the SSL code. The SSL documentation 13 * included with this distribution is covered by the same copyright terms 14 * except that the holder is Tim Hudson (tjh@cryptsoft.com). 15 * 16 * Copyright remains Eric Young's, and as such any Copyright notices in 17 * the code are not to be removed. 18 * If this package is used in a product, Eric Young should be given attribution 19 * as the author of the parts of the library used. 20 * This can be in the form of a textual message at program startup or 21 * in documentation (online or textual) provided with the package. 22 * 23 * Redistribution and use in source and binary forms, with or without 24 * modification, are permitted provided that the following conditions 25 * are met: 26 * 1. Redistributions of source code must retain the copyright 27 * notice, this list of conditions and the following disclaimer. 28 * 2. Redistributions in binary form must reproduce the above copyright 29 * notice, this list of conditions and the following disclaimer in the 30 * documentation and/or other materials provided with the distribution. 31 * 3. All advertising materials mentioning features or use of this software 32 * must display the following acknowledgement: 33 * "This product includes cryptographic software written by 34 * Eric Young (eay@cryptsoft.com)" 35 * The word 'cryptographic' can be left out if the rouines from the library 36 * being used are not cryptographic related :-). 37 * 4. If you include any Windows specific code (or a derivative thereof) from 38 * the apps directory (application code) you must include an acknowledgement: 39 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" 40 * 41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND 42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 44 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 51 * SUCH DAMAGE. 52 * 53 * The licence and distribution terms for any publically available version or 54 * derivative of this code cannot be changed. i.e. this code cannot simply be 55 * copied and put under another distribution licence 56 * [including the GNU Public Licence.] 57 */ 58 59#include <stdio.h> 60#include "cryptlib.h" 61#include "bn_lcl.h" 62 63static BIGNUM *euclid(BIGNUM *a, BIGNUM *b); 64 65int BN_gcd(BIGNUM *r, BIGNUM *in_a, BIGNUM *in_b, BN_CTX *ctx) 66 { 67 BIGNUM *a,*b,*t; 68 int ret=0; 69 70 bn_check_top(in_a); 71 bn_check_top(in_b); 72 73 BN_CTX_start(ctx); 74 a = BN_CTX_get(ctx); 75 b = BN_CTX_get(ctx); 76 if (a == NULL || b == NULL) goto err; 77 78 if (BN_copy(a,in_a) == NULL) goto err; 79 if (BN_copy(b,in_b) == NULL) goto err; 80 81 if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; } 82 t=euclid(a,b); 83 if (t == NULL) goto err; 84 85 if (BN_copy(r,t) == NULL) goto err; 86 ret=1; 87err: 88 BN_CTX_end(ctx); 89 return(ret); 90 } 91 92static BIGNUM *euclid(BIGNUM *a, BIGNUM *b) 93 { 94 BIGNUM *t; 95 int shifts=0; 96 97 bn_check_top(a); 98 bn_check_top(b); 99 100 for (;;) 101 { 102 if (BN_is_zero(b)) 103 break; 104 105 if (BN_is_odd(a)) 106 { 107 if (BN_is_odd(b)) 108 { 109 if (!BN_sub(a,a,b)) goto err; 110 if (!BN_rshift1(a,a)) goto err; 111 if (BN_cmp(a,b) < 0) 112 { t=a; a=b; b=t; } 113 } 114 else /* a odd - b even */ 115 { 116 if (!BN_rshift1(b,b)) goto err; 117 if (BN_cmp(a,b) < 0) 118 { t=a; a=b; b=t; } 119 } 120 } 121 else /* a is even */ 122 { 123 if (BN_is_odd(b)) 124 { 125 if (!BN_rshift1(a,a)) goto err; 126 if (BN_cmp(a,b) < 0) 127 { t=a; a=b; b=t; } 128 } 129 else /* a even - b even */ 130 { 131 if (!BN_rshift1(a,a)) goto err; 132 if (!BN_rshift1(b,b)) goto err; 133 shifts++; 134 } 135 } 136 } 137 if (shifts) 138 { 139 if (!BN_lshift(a,a,shifts)) goto err; 140 } 141 return(a); 142err: 143 return(NULL); 144 } 145 146/* solves ax == 1 (mod n) */ 147BIGNUM *BN_mod_inverse(BIGNUM *in, BIGNUM *a, const BIGNUM *n, BN_CTX *ctx) 148 { 149 BIGNUM *A,*B,*X,*Y,*M,*D,*R=NULL; 150 BIGNUM *T,*ret=NULL; 151 int sign; 152 153 bn_check_top(a); 154 bn_check_top(n); 155 156 BN_CTX_start(ctx); 157 A = BN_CTX_get(ctx); 158 B = BN_CTX_get(ctx); 159 X = BN_CTX_get(ctx); 160 D = BN_CTX_get(ctx); 161 M = BN_CTX_get(ctx); 162 Y = BN_CTX_get(ctx); 163 if (Y == NULL) goto err; 164 165 if (in == NULL) 166 R=BN_new(); 167 else 168 R=in; 169 if (R == NULL) goto err; 170 171 if (!BN_zero(X)) goto err; 172 if (!BN_one(Y)) goto err; 173 if (BN_copy(A,a) == NULL) goto err; 174 if (BN_copy(B,n) == NULL) goto err; 175 sign=1; 176 177 while (!BN_is_zero(B)) 178 { 179 if (!BN_div(D,M,A,B,ctx)) goto err; 180 T=A; 181 A=B; 182 B=M; 183 /* T has a struct, M does not */ 184 185 if (!BN_mul(T,D,X,ctx)) goto err; 186 if (!BN_add(T,T,Y)) goto err; 187 M=Y; 188 Y=X; 189 X=T; 190 sign= -sign; 191 } 192 if (sign < 0) 193 { 194 if (!BN_sub(Y,n,Y)) goto err; 195 } 196 197 if (BN_is_one(A)) 198 { if (!BN_mod(R,Y,n,ctx)) goto err; } 199 else 200 { 201 BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE); 202 goto err; 203 } 204 ret=R; 205err: 206 if ((ret == NULL) && (in == NULL)) BN_free(R); 207 BN_CTX_end(ctx); 208 return(ret); 209 } 210 211