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/**
 * Copyright 2003-2016 SSHTOOLS Limited. All Rights Reserved.
 *
 * For product documentation visit https://www.sshtools.com/
 *
 * This file is part of J2SSH Maverick.
 *
 * J2SSH Maverick 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 3 of the License, or
 * (at your option) any later version.
 *
 * J2SSH Maverick 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 J2SSH Maverick.  If not, see .
 */
package com.sshtools.ssh.components.jce;

import java.io.IOException;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.DSAPrivateKeySpec;

import com.sshtools.ssh.SshException;
import com.sshtools.ssh.components.SshDsaPrivateKey;
import com.sshtools.ssh.components.SshDsaPublicKey;
import com.sshtools.util.SimpleASNReader;

/**
 * DSA private key implementation for the SSH2 protocol.
 * 
 * @author Lee David Painter
 */
public class Ssh2DsaPrivateKey implements SshDsaPrivateKey {

	protected DSAPrivateKey prv;
	private Ssh2DsaPublicKey pub;

	public Ssh2DsaPrivateKey(DSAPrivateKey prv, DSAPublicKey pub) {
		this.prv = prv;
		this.pub = new Ssh2DsaPublicKey(pub);
	}

	public Ssh2DsaPrivateKey(BigInteger p, BigInteger q, BigInteger g,
			BigInteger x, BigInteger y) throws SshException {

		try {
			KeyFactory kf = JCEProvider
					.getProviderForAlgorithm(JCEAlgorithms.JCE_DSA) == null ? KeyFactory
					.getInstance(JCEAlgorithms.JCE_DSA) : KeyFactory
					.getInstance(JCEAlgorithms.JCE_DSA, JCEProvider
							.getProviderForAlgorithm(JCEAlgorithms.JCE_DSA));
			DSAPrivateKeySpec spec = new DSAPrivateKeySpec(x, p, q, g);
			prv = (DSAPrivateKey) kf.generatePrivate(spec);

			pub = new Ssh2DsaPublicKey(p, q, g, y);
		} catch (Throwable e) {
			throw new SshException(e);
		}

	}

	public byte[] sign(byte[] data) throws IOException {
		try {
			Signature l_sig = JCEProvider
					.getProviderForAlgorithm(JCEAlgorithms.JCE_SHA1WithDSA) == null ? Signature
					.getInstance(JCEAlgorithms.JCE_SHA1WithDSA)
					: Signature
							.getInstance(
									JCEAlgorithms.JCE_SHA1WithDSA,
									JCEProvider
											.getProviderForAlgorithm(JCEAlgorithms.JCE_SHA1WithDSA));
			l_sig.initSign(prv);
			l_sig.update(data);

			byte[] signature = l_sig.sign();

			SimpleASNReader asn = new SimpleASNReader(signature);
			asn.getByte();
			asn.getLength();
			asn.getByte();

			byte[] r = asn.getData();
			asn.getByte();

			byte[] s = asn.getData();

			byte[] decoded = null;
			int numSize = 32;
			if (r.length < numSize) {
				numSize = 28;
				if (r.length < numSize) {
					numSize = 20;
				}
			}

			decoded = new byte[numSize * 2];
			if (r.length >= numSize) {
				System.arraycopy(r, r.length - numSize, decoded, 0, numSize);
			} else {
				System.arraycopy(r, 0, decoded, numSize - r.length, r.length);
			}

			if (s.length >= numSize) {
				System.arraycopy(s, s.length - numSize, decoded, numSize,
						numSize);
			} else {
				System.arraycopy(s, 0, decoded, numSize + (numSize - s.length),
						s.length);
			}

			return decoded;
		} catch (Exception e) {
			throw new IOException("Failed to sign data! " + e.getMessage());
		}

	}

	public String getAlgorithm() {
		return "ssh-dss";
	}

	public SshDsaPublicKey getPublicKey() {
		return pub;
	}

	public BigInteger getX() {
		return prv.getX();
	}

}