1 /* crypto/bn/bn_gcd.c */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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.
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).
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.
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
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)"
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
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.]
63 static BIGNUM *euclid(BIGNUM *a, BIGNUM *b);
65 int BN_gcd(BIGNUM *r, BIGNUM *in_a, BIGNUM *in_b, BN_CTX *ctx)
76 if (a == NULL || b == NULL) goto err;
78 if (BN_copy(a,in_a) == NULL) goto err;
79 if (BN_copy(b,in_b) == NULL) goto err;
81 if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; }
83 if (t == NULL) goto err;
85 if (BN_copy(r,t) == NULL) goto err;
92 static BIGNUM *euclid(BIGNUM *a, BIGNUM *b)
109 if (!BN_sub(a,a,b)) goto err;
110 if (!BN_rshift1(a,a)) goto err;
114 else /* a odd - b even */
116 if (!BN_rshift1(b,b)) goto err;
125 if (!BN_rshift1(a,a)) goto err;
129 else /* a even - b even */
131 if (!BN_rshift1(a,a)) goto err;
132 if (!BN_rshift1(b,b)) goto err;
139 if (!BN_lshift(a,a,shifts)) goto err;
146 /* solves ax == 1 (mod n) */
147 BIGNUM *BN_mod_inverse(BIGNUM *in, BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
149 BIGNUM *A,*B,*X,*Y,*M,*D,*R=NULL;
163 if (Y == NULL) goto err;
169 if (R == NULL) goto err;
173 if (BN_copy(A,a) == NULL) goto err;
174 if (BN_copy(B,n) == NULL) goto err;
177 while (!BN_is_zero(B))
179 if (!BN_div(D,M,A,B,ctx)) goto err;
183 /* T has a struct, M does not */
185 if (!BN_mul(T,D,X,ctx)) goto err;
186 if (!BN_add(T,T,Y)) goto err;
194 if (!BN_sub(Y,n,Y)) goto err;
198 { if (!BN_mod(R,Y,n,ctx)) goto err; }
201 BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE);
206 if ((ret == NULL) && (in == NULL)) BN_free(R);