/* dsa.c  -  DSA signature algorithm
 *	Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <linux/kernel.h>
#include <linux/crypto/mpi.h>
#include <asm/errno.h>
#include "local.h"

/*****************************************************************************/
/*
 * perform DSA algorithm signature verification
 */
int DSA_verify(const MPI datahash, const MPI sig[], const MPI pkey[])
{
	MPI p, q, g, y, r, s;
	MPI w = NULL, u1 = NULL, u2 = NULL, v = NULL;
	MPI base[3];
	MPI exp[3];
	int rc;

	if (!datahash ||
	    !sig[0] || !sig[1] ||
	    !pkey[0] || !pkey[1] || !pkey[2] || !pkey[3]
	    )
		return -EINVAL;

	p = pkey[0];	/* prime */
	q = pkey[1];	/* group order */
	g = pkey[2];	/* group generator */
	y = pkey[3];	/* g^x mod p */
	r = sig[0];
	s = sig[1];

	if (!(mpi_cmp_ui(r, 0) > 0 && mpi_cmp(r, q) < 0)) {
		printk("DSA_verify assertion failed [0 < r < q]\n");
		return -EPERM;
	}

	if (!(mpi_cmp_ui(s, 0) > 0 && mpi_cmp(s, q) < 0)) {
		printk("DSA_verify assertion failed [0 < s < q]\n");
		return -EPERM;
	}

	rc = -ENOMEM;
	w  = mpi_alloc(mpi_get_nlimbs(q)); if (!w ) goto cleanup;
	u1 = mpi_alloc(mpi_get_nlimbs(q)); if (!u1) goto cleanup;
	u2 = mpi_alloc(mpi_get_nlimbs(q)); if (!u2) goto cleanup;
	v  = mpi_alloc(mpi_get_nlimbs(p)); if (!v ) goto cleanup;

	/* w = s^(-1) mod q */
	if (mpi_invm(w, s, q) < 0)
		goto cleanup;

	/* u1 = (datahash * w) mod q */
	if (mpi_mulm(u1, datahash, w, q) < 0)
		goto cleanup;

	/* u2 = r * w mod q  */
	if (mpi_mulm(u2, r, w, q) < 0)
		goto cleanup;

	/* v =  g^u1 * y^u2 mod p mod q */
	base[0] = g;	exp[0] = u1;
	base[1] = y;	exp[1] = u2;
	base[2] = NULL;	exp[2] = NULL;

	if (mpi_mulpowm(v, base, exp, p) < 0)
		goto cleanup;

	if (mpi_fdiv_r(v, v, q) < 0)
		goto cleanup;

	rc = mpi_cmp(v, r) == 0 ? 0 : -EPERM;

 cleanup:
	mpi_free(w);
	mpi_free(u1);
	mpi_free(u2);
	mpi_free(v);
	return rc;
} /* end DSA_verify() */