/*
 * Copyright 1999-2007 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.crypto.provider;

import java.security.SecureRandom;
import java.security.InvalidParameterException;
import java.security.InvalidAlgorithmParameterException;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.KeyGeneratorSpi;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

/**
 * This class generates a secret key for use with the HMAC-MD5 algorithm.
 *
 * @author Jan Luehe
 *
 */

public final class HmacMD5KeyGenerator extends KeyGeneratorSpi {

    private SecureRandom random = null;
    private int keysize = 64; // default keysize (in number of bytes)

    /**
     * Verify the SunJCE provider in the constructor.
     *
     * @exception SecurityException if fails to verify
     * its own integrity
     */
    public HmacMD5KeyGenerator() {
        if (!SunJCE.verifySelfIntegrity(this.getClass())) {
            throw new SecurityException("The SunJCE provider may have " +
                                        "been tampered.");
        }
    }

    /**
     * Initializes this key generator.
     *
     * @param random the source of randomness for this generator
     */
    protected void engineInit(SecureRandom random) {
        this.random = random;
    }

    /**
     * Initializes this key generator with the specified parameter
     * set and a user-provided source of randomness.
     *
     * @param params the key generation parameters
     * @param random the source of randomness for this key generator
     *
     * @exception InvalidAlgorithmParameterException if <code>params</code> is
     * inappropriate for this key generator
     */
    protected void engineInit(AlgorithmParameterSpec params,
                              SecureRandom random)
        throws InvalidAlgorithmParameterException
    {
        throw new InvalidAlgorithmParameterException
            ("HMAC-MD5 key generation does not take any parameters");
    }

    /**
     * Initializes this key generator for a certain keysize, using the given
     * source of randomness.
     *
     * @param keysize the keysize. This is an algorithm-specific
     * metric specified in number of bits.
     * @param random the source of randomness for this key generator
     */
    protected void engineInit(int keysize, SecureRandom random) {
        this.keysize = (keysize+7) / 8;
        this.engineInit(random);
    }

    /**
     * Generates an HMAC-MD5 key.
     *
     * @return the new HMAC-MD5 key
     */
    protected SecretKey engineGenerateKey() {
        if (this.random == null) {
            this.random = SunJCE.RANDOM;
        }

        byte[] keyBytes = new byte[this.keysize];
        this.random.nextBytes(keyBytes);

        return new SecretKeySpec(keyBytes, "HmacMD5");
    }
}