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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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

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 * 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).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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package com.sun.crypto.provider;

import java.math.BigInteger;

import java.security.*;

import java.security.spec.*;

import javax.crypto.spec.DHParameterSpec;

import javax.crypto.spec.DHGenParameterSpec;

import static sun.security.util.SecurityProviderConstants.DEF_DH_KEY_SIZE;

/*

 * This class generates parameters for the Diffie-Hellman algorithm.

 * The parameters are a prime, a base, and optionally the length in bits of

 * the private value.

 *

 * <p>The Diffie-Hellman parameter generation accepts the size in bits of the

 * prime modulus and the size in bits of the random exponent as input.

 *

 * @author Jan Luehe

 *

 *

 * @see java.security.AlgorithmParameters

 * @see java.security.spec.AlgorithmParameterSpec

 * @see DHParameters

 */

public final class DHParameterGenerator extends AlgorithmParameterGeneratorSpi {

    // The size in bits of the prime modulus

    private int primeSize = DEF_DH_KEY_SIZE;

    // The size in bits of the random exponent (private value)

    private int exponentSize = 0;

    // The source of randomness

    private SecureRandom random = null;

    private static void checkKeySize(int keysize)

            throws InvalidParameterException {

        boolean supported = ((keysize == 2048) || (keysize == 3072) ||

            ((keysize >= 512) && (keysize <= 1024) && ((keysize & 0x3F) == 0)));

        if (!supported) {

            throw new InvalidParameterException(

                    "DH key size must be multiple of 64 and range " +

                    "from 512 to 1024 (inclusive), or 2048, 3072. " +

                    "The specific key size " + keysize + " is not supported");

        }

    }

    /**

     * Initializes this parameter generator for a certain keysize

     * and source of randomness.

     * The keysize is specified as the size in bits of the prime modulus.

     *

     * @param keysize the keysize (size of prime modulus) in bits

     * @param random the source of randomness

     */

    @Override

    protected void engineInit(int keysize, SecureRandom random) {

        checkKeySize(keysize);

        this.primeSize = keysize;

        this.random = random;

    }

    /**

     * Initializes this parameter generator with a set of parameter

     * generation values, which specify the size of the prime modulus and

     * the size of the random exponent, both in bits.

     *

     * @param genParamSpec the set of parameter generation values

     * @param random the source of randomness

     *

     * @exception InvalidAlgorithmParameterException if the given parameter

     * generation values are inappropriate for this parameter generator

     */

    @Override

    protected void engineInit(AlgorithmParameterSpec genParamSpec,

          SecureRandom random) throws InvalidAlgorithmParameterException {

        if (!(genParamSpec instanceof DHGenParameterSpec)) {

            throw new InvalidAlgorithmParameterException

                ("Inappropriate parameter type");

        }

        DHGenParameterSpec dhParamSpec = (DHGenParameterSpec)genParamSpec;

        primeSize = dhParamSpec.getPrimeSize();

        exponentSize = dhParamSpec.getExponentSize();

        if ((exponentSize <= 0) || (exponentSize >= primeSize)) {

            throw new InvalidAlgorithmParameterException(

                    "Exponent size (" + exponentSize +

                    ") must be positive and less than modulus size (" +

                    primeSize + ")");

        }

        try {

            checkKeySize(primeSize);

        } catch (InvalidParameterException ipe) {

            throw new InvalidAlgorithmParameterException(ipe.getMessage());

        }

        this.random = random;

    }

    /**

     * Generates the parameters.

     *

     * @return the new AlgorithmParameters object

     */

    @Override

    protected AlgorithmParameters engineGenerateParameters() {

        if (this.exponentSize == 0) {

            this.exponentSize = this.primeSize - 1;

        }

        if (random == null) {

            random = SunJCE.getRandom();

        }

        BigInteger paramP = null;

        BigInteger paramG = null;

        try {

            AlgorithmParameterGenerator dsaParamGen =

                    AlgorithmParameterGenerator.getInstance("DSA");

            dsaParamGen.init(primeSize, random);

            AlgorithmParameters dsaParams = dsaParamGen.generateParameters();

            DSAParameterSpec dsaParamSpec =

                    dsaParams.getParameterSpec(DSAParameterSpec.class);

            DHParameterSpec dhParamSpec;

            if (this.exponentSize > 0) {

                dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),

                                                  dsaParamSpec.getG(),

                                                  this.exponentSize);

            } else {

                dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),

                                                  dsaParamSpec.getG());

            }

            AlgorithmParameters algParams =

                    AlgorithmParameters.getInstance("DH", SunJCE.getInstance());

            algParams.init(dhParamSpec);

            return algParams;

        } catch (Exception ex) {

            throw new ProviderException("Unexpected exception", ex);

        }

    }

}