messagedigest.java

一个非常好的ssh客户端实现

/******************************************************************************
 *
 * Copyright (c) 1999-2003 AppGate Network Security AB. All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code as
 * defined in and that are subject to the MindTerm Public Source License,
 * Version 2.0, (the 'License'). You may not use this file except in compliance
 * with the License.
 * 
 * You should have received a copy of the MindTerm Public Source License
 * along with this software; see the file LICENSE.  If not, write to
 * AppGate Network Security AB, Otterhallegatan 2, SE-41118 Goteborg, SWEDEN
 *
 *****************************************************************************/

package com.mindbright.jca.security;

public abstract class MessageDigest extends MessageDigestSpi {

    protected String           algorithm;
    protected Provider         provider;

    protected MessageDigest(String algorithm) {
	this.algorithm = algorithm;
    }

    public static MessageDigest getInstance(String algorithm)
	throws NoSuchAlgorithmException
    {
	try {
	    String provider =
		ProviderLookup.findImplementingProvider("MessageDigest",
							algorithm);
	    return getInstance(algorithm, provider);
	} catch (NoSuchProviderException e) {
	    throw new Error("Error in MessageDigest: " + e);
	}
    }

    public static MessageDigest getInstance(String algorithm,
					    String provider)
	throws NoSuchAlgorithmException, NoSuchProviderException
    {
	ProviderLookup pl = ProviderLookup.getImplementation("MessageDigest",
							     algorithm,
							     provider);
	MessageDigest md = (MessageDigest) pl.getImpl();
	md.provider      = pl.getProvider();
	md.engineReset();
	return md;
    }

    public byte[] digest() {
	return engineDigest();
    }

    public byte[] digest(byte[] input) {
	engineUpdate(input, 0, input.length);
	return engineDigest();
    }

    public int digest(byte[] buf, int offset, int len) throws DigestException {
	return engineDigest(buf, offset, len);
    }

    public void reset() {
	engineReset();
    }

    public void update(byte input) {
	engineUpdate(input);
    }

    public void update(byte[] input) {
	engineUpdate(input, 0, input.length);
    }

    public void update(byte[] input, int offset, int len) {
	engineUpdate(input, offset, len);
    }

    public final Provider getProvider() {
	return provider;
    }

    public final String getAlgorithm() {
	return algorithm;
    }

    public final int getDigestLength() {
	return engineGetDigestLength();
    }

    public static boolean isEqual(byte[] digesta, byte[] digestb) {
	if(digesta.length != digestb.length)
	    return false;

	for(int i = 0; i < digesta.length; i++) {
	    if(digesta[i] != digestb[i]) {
		return false;
	    }
	}
	return true;
    }

    public String toString() {
	return provider.getName() + " (" + provider.getVersion() +
	    ") MessageDigest." + algorithm;
    }

    public Object clone() throws CloneNotSupportedException {
	if(this instanceof Cloneable) {
	    return super.clone();
	} else {
	    throw new CloneNotSupportedException();
	}
    }

}