source: trunk/cscrypt/bn_exp.c@ 1

/* crypto/bn/bn_exp.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.]
 */
/* ====================================================================
 * Copyright (c) 1998-2000 The OpenSSL Project.  All rights reserved.
 *
 * 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 above 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 acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@openssl.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED 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 OpenSSL PROJECT OR
 * ITS 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.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */


#include <stdio.h>
#include "bn_lcl.h"

#define TABLE_SIZE  32

/* slow but works */
int BN_mod_mul(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m, BN_CTX *ctx)
    {
    BIGNUM *t;
    int r=0;

    bn_check_top(a);
    bn_check_top(b);
    bn_check_top(m);

    BN_CTX_start(ctx);
    if ((t = BN_CTX_get(ctx)) == NULL) goto err;
    if (a == b)
        { if (!BN_sqr(t,a,ctx)) goto err; }
    else
        { if (!BN_mul(t,a,b,ctx)) goto err; }
    if (!BN_mod(ret,t,m,ctx)) goto err;
    r=1;
err:
    BN_CTX_end(ctx);
    return(r);
    }


int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
           BN_CTX *ctx)
    {
    int ret;

    bn_check_top(a);
    bn_check_top(p);
    bn_check_top(m);

    ret=BN_mod_exp_simple(r,a,p,m,ctx);

    return(ret);
    }





/* The old fallback, simple version :-) */
int BN_mod_exp_simple(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
         BN_CTX *ctx)
    {
    int i,j,bits,ret=0,wstart,wend,window,wvalue,ts=0;
    int start=1;
    BIGNUM *d;
    BIGNUM val[TABLE_SIZE];

    bits=BN_num_bits(p);

    if (bits == 0)
        {
        BN_one(r);
        return(1);
        }

    BN_CTX_start(ctx);
    if ((d = BN_CTX_get(ctx)) == NULL) goto err;

    BN_init(&(val[0]));
    ts=1;
    if (!BN_mod(&(val[0]),a,m,ctx)) goto err;       /* 1 */

    window = BN_window_bits_for_exponent_size(bits);
    if (window > 1)
        {
        if (!BN_mod_mul(d,&(val[0]),&(val[0]),m,ctx))
            goto err;               /* 2 */
        j=1<<(window-1);
        for (i=1; i<j; i++)
            {
            BN_init(&(val[i]));
            if (!BN_mod_mul(&(val[i]),&(val[i-1]),d,m,ctx))
                goto err;
            }
        ts=i;
        }

    start=1;    /* This is used to avoid multiplication etc
             * when there is only the value '1' in the
             * buffer. */
    wvalue=0;   /* The 'value' of the window */
    wstart=bits-1;  /* The top bit of the window */
    wend=0;     /* The bottom bit of the window */

    if (!BN_one(r)) goto err;

    for (;;)
        {
        if (BN_is_bit_set(p,wstart) == 0)
            {
            if (!start)
                if (!BN_mod_mul(r,r,r,m,ctx))
                goto err;
            if (wstart == 0) break;
            wstart--;
            continue;
            }
        /* We now have wstart on a 'set' bit, we now need to work out
         * how bit a window to do.  To do this we need to scan
         * forward until the last set bit before the end of the
         * window */
        j=wstart;
        wvalue=1;
        wend=0;
        for (i=1; i<window; i++)
            {
            if (wstart-i < 0) break;
            if (BN_is_bit_set(p,wstart-i))
                {
                wvalue<<=(i-wend);
                wvalue|=1;
                wend=i;
                }
            }

        /* wend is the size of the current window */
        j=wend+1;
        /* add the 'bytes above' */
        if (!start)
            for (i=0; i<j; i++)
                {
                if (!BN_mod_mul(r,r,r,m,ctx))
                    goto err;
                }
        
        /* wvalue will be an odd number < 2^window */
        if (!BN_mod_mul(r,r,&(val[wvalue>>1]),m,ctx))
            goto err;

        /* move the 'window' down further */
        wstart-=wend+1;
        wvalue=0;
        start=0;
        if (wstart < 0) break;
        }
    ret=1;
err:
    BN_CTX_end(ctx);
    for (i=0; i<ts; i++)
        BN_clear_free(&(val[i]));
    return(ret);
    }