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elgamal.c
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/
elgamal.c
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/*
* Copyright (c) 1999, 2000, 2001, 2002 X-Way Rights BV
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
/*!\file elgamal.c
* \brief ElGamal algorithm.
* \author Bob Deblier <bob.deblier@telenet.be>
*/
#define BEECRYPT_DLL_EXPORT
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include "beecrypt/elgamal.h"
#include "beecrypt/dldp.h"
int elgv1sign(const mpbarrett* p, const mpbarrett* n, const mpnumber* g, randomGeneratorContext* rgc, const mpnumber* hm, const mpnumber* x, mpnumber* r, mpnumber* s)
{
register size_t size = p->size;
register mpw* temp = (mpw*) malloc((8*size+6)*sizeof(mpw));
if (temp)
{
/* get a random k, invertible modulo (p-1) */
mpbrndinv_w(n, rgc, temp, temp+size, temp+2*size);
/* compute r = g^k mod p */
mpnfree(r);
mpnsize(r, size);
mpbpowmod_w(p, g->size, g->data, size, temp, r->data, temp+2*size);
/* compute x*r mod n */
mpbmulmod_w(n, x->size, x->data, r->size, r->data, temp, temp+2*size);
/* compute -(x*r) mod n */
mpneg(size, temp);
mpadd(size, temp, n->modl);
/* compute h(m) - x*r mod n */
mpbaddmod_w(n, hm->size, hm->data, size, temp, temp, temp+2*size);
/* compute s = inv(k)*(h(m) - x*r) mod n */
mpnfree(s);
mpnsize(s, size);
mpbmulmod_w(n, size, temp, size, temp+size, s->data, temp+2*size);
free(temp);
return 0;
}
return -1;
}
int elgv1vrfy(const mpbarrett* p, const mpbarrett* n, const mpnumber* g, const mpnumber* hm, const mpnumber* y, const mpnumber* r, const mpnumber* s)
{
register size_t size = p->size;
register mpw* temp;
if (mpz(r->size, r->data))
return 0;
if (mpgex(r->size, r->data, size, p->modl))
return 0;
if (mpz(s->size, s->data))
return 0;
if (mpgex(s->size, s->data, n->size, n->modl))
return 0;
temp = (mpw*) malloc((6*size+2)*sizeof(mpw));
if (temp)
{
register int rc;
/* compute u1 = y^r mod p */
mpbpowmod_w(p, y->size, y->data, r->size, r->data, temp, temp+2*size);
/* compute u2 = r^s mod p */
mpbpowmod_w(p, r->size, r->data, s->size, s->data, temp+size, temp+2*size);
/* compute v1 = u1*u2 mod p */
mpbmulmod_w(p, size, temp, size, temp+size, temp+size, temp+2*size);
/* compute v2 = g^h(m) mod p */
mpbpowmod_w(p, g->size, g->data, hm->size, hm->data, temp, temp+2*size);
rc = mpeq(size, temp, temp+size);
free(temp);
return rc;
}
return 0;
}
int elgv3sign(const mpbarrett* p, const mpbarrett* n, const mpnumber* g, randomGeneratorContext* rgc, const mpnumber* hm, const mpnumber* x, mpnumber* r, mpnumber* s)
{
register size_t size = p->size;
register mpw* temp = (mpw*) malloc((6*size+2)*sizeof(mpw));
if (temp)
{
/* get a random k */
mpbrnd_w(p, rgc, temp, temp+2*size);
/* compute r = g^k mod p */
mpnfree(r);
mpnsize(r, size);
mpbpowmod_w(p, g->size, g->data, size, temp, r->data, temp+2*size);
/* compute u1 = x*r mod n */
mpbmulmod_w(n, x->size, x->data, size, r->data, temp+size, temp+2*size);
/* compute u2 = k*h(m) mod n */
mpbmulmod_w(n, size, temp, hm->size, hm->data, temp, temp+2*size);
/* compute s = u1+u2 mod n */
mpnfree(s);
mpnsize(s, n->size);
mpbaddmod_w(n, size, temp, size, temp+size, s->data, temp+2*size);
free(temp);
return 0;
}
return -1;
}
int elgv3vrfy(const mpbarrett* p, const mpbarrett* n, const mpnumber* g, const mpnumber* hm, const mpnumber* y, const mpnumber* r, const mpnumber* s)
{
register size_t size = p->size;
register mpw* temp;
if (mpz(r->size, r->data))
return 0;
if (mpgex(r->size, r->data, size, p->modl))
return 0;
if (mpz(s->size, s->data))
return 0;
if (mpgex(s->size, s->data, n->size, n->modl))
return 0;
temp = (mpw*) malloc((6*size+2)*sizeof(mpw));
if (temp)
{
register int rc;
/* compute u1 = y^r mod p */
mpbpowmod_w(p, y->size, y->data, r->size, r->data, temp, temp+2*size);
/* compute u2 = r^h(m) mod p */
mpbpowmod_w(p, r->size, r->data, hm->size, hm->data, temp+size, temp+2*size);
/* compute v2 = u1*u2 mod p */
mpbmulmod_w(p, size, temp, size, temp+size, temp+size, temp+2*size);
/* compute v1 = g^s mod p */
mpbpowmod_w(p, g->size, g->data, s->size, s->data, temp, temp+2*size);
rc = mpeq(size, temp, temp+size);
free(temp);
return rc;
}
return 0;
}
/*!\}
*/