/*

 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package com.sun.crypto.provider;

import java.security.SecureRandom;

import java.security.InvalidParameterException;

import java.security.InvalidAlgorithmParameterException;

import java.security.InvalidKeyException;

import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.KeyGeneratorSpi;

import javax.crypto.SecretKey;

import javax.crypto.spec.DESKeySpec;

/**

 * This class generates a DES key.

 *

 * @author Jan Luehe

 *

 */

public final class DESKeyGenerator extends KeyGeneratorSpi {

    private SecureRandom random = null;

    /**

     * Empty constructor

     */

    public DESKeyGenerator() {

    }

    /**

     * 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

                ("DES 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) {

        if (keysize != 56) {

            throw new InvalidParameterException("Wrong keysize: must "

                                                + "be equal to 56");

        }

        this.engineInit(random);

    }

    /**

     * Generates the DES key.

     *

     * @return the new DES key

     */

    protected SecretKey engineGenerateKey() {

        DESKey desKey = null;

        if (this.random == null) {

            this.random = SunJCE.getRandom();

        }

        try {

            byte[] key = new byte[DESKeySpec.DES_KEY_LEN];

            do {

                this.random.nextBytes(key);

                setParityBit(key, 0);

            } while (DESKeySpec.isWeak(key, 0));

            desKey = new DESKey(key);

        } catch (InvalidKeyException e) {

            // this is never thrown

        }

        return desKey;

    }

    /*

     * Does parity adjustment, using bit in position 8 as the parity bit,

     * for 8 key bytes, starting at <code>offset</code>.

     *

     * The 8 parity bits of a DES key are only used for sanity-checking

     * of the key, to see if the key could actually be a key. If you check

     * the parity of the quantity, and it winds up not having the correct

     * parity, then you'll know something went wrong.

     *

     * A key that is not parity adjusted (e.g. e4e4e4e4e4e4e4e4) produces the

     * same output as a key that is parity adjusted (e.g. e5e5e5e5e5e5e5e5),

     * because it is the 56 bits of the DES key that are cryptographically

     * significant/"effective" -- the other 8 bits are just used for parity

     * checking.

     */

    static void setParityBit(byte[] key, int offset) {

        if (key == null)

            return;

        for (int i = 0; i < DESKeySpec.DES_KEY_LEN; i++) {

            int b = key[offset] & 0xfe;

            b |= (Integer.bitCount(b) & 1) ^ 1;

            key[offset++] = (byte)b;

        }

    }

}