bn_recp.c revision 656d9c7f52f88b3a3daccafa7655dec086c4756e 
1/* crypto/bn/bn_recp.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
63void BN_RECP_CTX_init(BN_RECP_CTX *recp)
64	{
65	BN_init(&(recp->N));
66	BN_init(&(recp->Nr));
67	recp->num_bits=0;
68	recp->flags=0;
69	}
70
71BN_RECP_CTX *BN_RECP_CTX_new(void)
72	{
73	BN_RECP_CTX *ret;
74
75	if ((ret=(BN_RECP_CTX *)OPENSSL_malloc(sizeof(BN_RECP_CTX))) == NULL)
76		return(NULL);
77
78	BN_RECP_CTX_init(ret);
79	ret->flags=BN_FLG_MALLOCED;
80	return(ret);
81	}
82
83void BN_RECP_CTX_free(BN_RECP_CTX *recp)
84	{
85	if(recp == NULL)
86	    return;
87
88	BN_free(&(recp->N));
89	BN_free(&(recp->Nr));
90	if (recp->flags & BN_FLG_MALLOCED)
91		OPENSSL_free(recp);
92	}
93
94int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *d, BN_CTX *ctx)
95	{
96	if (!BN_copy(&(recp->N),d)) return 0;
97	BN_zero(&(recp->Nr));
98	recp->num_bits=BN_num_bits(d);
99	recp->shift=0;
100	return(1);
101	}
102
103int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,
104	BN_RECP_CTX *recp, BN_CTX *ctx)
105	{
106	int ret=0;
107	BIGNUM *a;
108	const BIGNUM *ca;
109
110	BN_CTX_start(ctx);
111	if ((a = BN_CTX_get(ctx)) == NULL) goto err;
112	if (y != NULL)
113		{
114		if (x == y)
115			{ if (!BN_sqr(a,x,ctx)) goto err; }
116		else
117			{ if (!BN_mul(a,x,y,ctx)) goto err; }
118		ca = a;
119		}
120	else
121		ca=x; /* Just do the mod */
122
123	ret = BN_div_recp(NULL,r,ca,recp,ctx);
124err:
125	BN_CTX_end(ctx);
126	bn_check_top(r);
127	return(ret);
128	}
129
130int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m,
131	BN_RECP_CTX *recp, BN_CTX *ctx)
132	{
133	int i,j,ret=0;
134	BIGNUM *a,*b,*d,*r;
135
136	BN_CTX_start(ctx);
137	a=BN_CTX_get(ctx);
138	b=BN_CTX_get(ctx);
139	if (dv != NULL)
140		d=dv;
141	else
142		d=BN_CTX_get(ctx);
143	if (rem != NULL)
144		r=rem;
145	else
146		r=BN_CTX_get(ctx);
147	if (a == NULL || b == NULL || d == NULL || r == NULL) goto err;
148
149	if (BN_ucmp(m,&(recp->N)) < 0)
150		{
151		BN_zero(d);
152		if (!BN_copy(r,m)) return 0;
153		BN_CTX_end(ctx);
154		return(1);
155		}
156
157	/* We want the remainder
158	 * Given input of ABCDEF / ab
159	 * we need multiply ABCDEF by 3 digests of the reciprocal of ab
160	 *
161	 */
162
163	/* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
164	i=BN_num_bits(m);
165	j=recp->num_bits<<1;
166	if (j>i) i=j;
167
168	/* Nr := round(2^i / N) */
169	if (i != recp->shift)
170		recp->shift=BN_reciprocal(&(recp->Nr),&(recp->N),
171			i,ctx); /* BN_reciprocal returns i, or -1 for an error */
172	if (recp->shift == -1) goto err;
173
174	/* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|
175	 *    = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|
176	 *   <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|
177	 *    = |m/N|
178	 */
179	if (!BN_rshift(a,m,recp->num_bits)) goto err;
180	if (!BN_mul(b,a,&(recp->Nr),ctx)) goto err;
181	if (!BN_rshift(d,b,i-recp->num_bits)) goto err;
182	d->neg=0;
183
184	if (!BN_mul(b,&(recp->N),d,ctx)) goto err;
185	if (!BN_usub(r,m,b)) goto err;
186	r->neg=0;
187
188#if 1
189	j=0;
190	while (BN_ucmp(r,&(recp->N)) >= 0)
191		{
192		if (j++ > 2)
193			{
194			BNerr(BN_F_BN_DIV_RECP,BN_R_BAD_RECIPROCAL);
195			goto err;
196			}
197		if (!BN_usub(r,r,&(recp->N))) goto err;
198		if (!BN_add_word(d,1)) goto err;
199		}
200#endif
201
202	r->neg=BN_is_zero(r)?0:m->neg;
203	d->neg=m->neg^recp->N.neg;
204	ret=1;
205err:
206	BN_CTX_end(ctx);
207	bn_check_top(dv);
208	bn_check_top(rem);
209	return(ret);
210	}
211
212/* len is the expected size of the result
213 * We actually calculate with an extra word of precision, so
214 * we can do faster division if the remainder is not required.
215 */
216/* r := 2^len / m */
217int BN_reciprocal(BIGNUM *r, const BIGNUM *m, int len, BN_CTX *ctx)
218	{
219	int ret= -1;
220	BIGNUM *t;
221
222	BN_CTX_start(ctx);
223	if((t = BN_CTX_get(ctx)) == NULL) goto err;
224
225	if (!BN_set_bit(t,len)) goto err;
226
227	if (!BN_div(r,NULL,t,m,ctx)) goto err;
228
229	ret=len;
230err:
231	bn_check_top(r);
232	BN_CTX_end(ctx);
233	return(ret);
234	}
235