hmac.java

来自「一个非常好的ssh客户端实现」· Java 代码 · 共 165 行

/******************************************************************************
 *
 * 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.security.mac;

import com.mindbright.jca.security.Key;
import com.mindbright.jca.security.MessageDigest;
import com.mindbright.jca.security.DigestException;
import com.mindbright.jca.security.InvalidKeyException;
import com.mindbright.jca.security.InvalidAlgorithmParameterException;
import com.mindbright.jca.security.spec.AlgorithmParameterSpec;

import com.mindbright.jce.crypto.spec.SecretKeySpec;
import com.mindbright.jce.crypto.MacSpi;

/**
 * Class implementing message authentication through keyed hashing
 * (referred to as HMAC) described in rfc2104
 */
public class HMAC extends MacSpi {

    protected int macLength;
    protected int hashLength;
    protected int blockSize;

    protected byte[] k_ipad;
    protected byte[] k_opad;

    protected byte[] innerHash;
    protected byte[] outerHash;

    protected MessageDigest inner;
    protected MessageDigest outer;
    protected MessageDigest innerClone;
    protected MessageDigest outerClone;

    protected HMAC(String hashAlgorithm) {
	try {
	    inner = MessageDigest.getInstance(hashAlgorithm);
	    outer = MessageDigest.getInstance(hashAlgorithm);
	} catch (Exception e) {
	    throw new Error("Error in HMAC: " + e);
	}

	macLength = inner.getDigestLength();
	blockSize = 64; // Bad API... would like inner.blockSize()

	hashLength = macLength;
	innerHash  = new byte[hashLength];
	outerHash  = new byte[hashLength];

	k_ipad = new byte[blockSize];
	k_opad = new byte[blockSize];
    }

    private final void init(byte[] key) {
	inner.reset();
	outer.reset();

	int keyLen = key.length;

	if(keyLen > blockSize) {
	    inner.update(key);
	    key = inner.digest();
	    inner.reset();
	    keyLen = blockSize;
	}

	System.arraycopy(key, 0, k_ipad, 0, keyLen);
	System.arraycopy(key, 0, k_opad, 0, keyLen);

	for(int i = 0; i < blockSize; i++) {
	    k_ipad[i] ^= (byte)0x36;
	    k_opad[i] ^= (byte)0x5c;
	}

	updatePads();

	if(inner instanceof Cloneable) {
	    try {
		innerClone = (MessageDigest)inner.clone();
		outerClone = (MessageDigest)outer.clone();
	    } catch (CloneNotSupportedException e) {
		innerClone = null;
		outerClone = null;
	    }
	}
    }

    protected final byte[] engineDoFinal() {
	byte[] hmac;

	try {
	    inner.digest(innerHash, 0, hashLength);
	    outer.update(innerHash, 0, hashLength);
	    outer.digest(outerHash, 0, hashLength);
	} catch (DigestException e) {
	    throw new Error("Error/bug in HMAC, buffer too short");
	}

	// This copy could be avoided if MessageDigest would be defined
	// to support shorter buffer (see API doc)
	//
	hmac = new byte[macLength];
	System.arraycopy(outerHash, 0, hmac, 0, macLength);

	updatePads();

	return hmac;
    }

    protected final int engineGetMacLength() {
	return macLength;
    }

    protected final void engineInit(Key key, AlgorithmParameterSpec params)
	throws InvalidKeyException, InvalidAlgorithmParameterException {
	init(((SecretKeySpec)key).getEncoded());
    }

    protected final void engineReset() {
	updatePads();
    }

    protected final void engineUpdate(byte input) {
	engineUpdate(new byte[] { input }, 0, 1);
    }

    protected final void engineUpdate(byte[] input, int offset, int len) {
	inner.update(input, offset, len);
    }

    private final void updatePads() {
	if(innerClone != null) {
	    try {
		inner = (MessageDigest)innerClone.clone();
		outer = (MessageDigest)outerClone.clone();
	    } catch (CloneNotSupportedException e) {
		innerClone = null;
		outerClone = null;
		updatePads();
	    }
	} else {
	    inner.reset();
	    outer.reset();
	    inner.update(k_ipad);
	    outer.update(k_opad);
	}
    }


}