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/* DiffieHellmanImpl.java -- implementation of the Diffie-Hellman key agreement.

   Copyright (C) 2005, 2006  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.javax.crypto.jce;

import java.math.BigInteger;

import java.security.InvalidKeyException;

import java.security.Key;

import java.security.SecureRandom;

import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.KeyAgreementSpi;

import javax.crypto.SecretKey;

import javax.crypto.ShortBufferException;

import javax.crypto.interfaces.DHPrivateKey;

import javax.crypto.interfaces.DHPublicKey;

import javax.crypto.spec.DHParameterSpec;

import javax.crypto.spec.SecretKeySpec;

/**

 * The JCE implementation of a 2-party Diffie-Hellman key agreement.

 *

 * @author Casey Marshall (csm@gnu.org)

 */

public final class DiffieHellmanImpl

    extends KeyAgreementSpi

{

  /** The private key being used for this agreement. */

  private DHPrivateKey key;

  /** The current result. */

  private byte[] result;

  /** True if the caller told us we are done. */

  private boolean last_phase_done;

  /** Trivial default constructor. */

  public DiffieHellmanImpl()

  {

    super();

    key = null;

    result = null;

    last_phase_done = false;

  }

  protected Key engineDoPhase(Key incoming, boolean lastPhase)

      throws InvalidKeyException

  {

    if (key == null)

      throw new IllegalStateException("Not initialized");

    if (last_phase_done)

      throw new IllegalStateException("Last phase already done");

    if (! (incoming instanceof DHPublicKey))

      throw new InvalidKeyException("Key MUST be a DHPublicKey");

    DHPublicKey pub = (DHPublicKey) incoming;

    DHParameterSpec s1 = key.getParams();

    DHParameterSpec s2 = pub.getParams();

    if (! s1.getG().equals(s2.getG()) || ! s1.getP().equals(s2.getP()))

      throw new InvalidKeyException("Incompatible key");

    if (! lastPhase)

      throw new IllegalArgumentException(

          "This key-agreement MUST be concluded in one step only");

    BigInteger resultBI = pub.getY().modPow(key.getX(), s1.getP());

    result = resultBI.toByteArray();

    if (result[0] == 0x00)

      {

        byte[] buf = new byte[result.length - 1];

        System.arraycopy(result, 1, buf, 0, buf.length);

        result = buf;

      }

    last_phase_done = true;

    return null;

  }

  protected byte[] engineGenerateSecret()

  {

    checkState();

    byte[] res = (byte[]) result.clone();

    reset();

    return res;

  }

  protected int engineGenerateSecret(byte[] secret, int offset)

      throws ShortBufferException

  {

    checkState();

    if (result.length > secret.length - offset)

      throw new ShortBufferException();

    System.arraycopy(result, 0, secret, offset, result.length);

    int res = result.length;

    reset();

    return res;

  }

  protected SecretKey engineGenerateSecret(String algorithm)

      throws InvalidKeyException

  {

    checkState();

    byte[] s = (byte[]) result.clone();

    SecretKey res = new SecretKeySpec(s, algorithm);

    reset();

    return res;

  }

  protected void engineInit(Key key, SecureRandom random)

      throws InvalidKeyException

  {

    if (! (key instanceof DHPrivateKey))

      throw new InvalidKeyException("Key MUST be a DHPrivateKey");

    this.key = (DHPrivateKey) key;

    reset();

  }

  protected void engineInit(Key key, AlgorithmParameterSpec params,

                            SecureRandom random)

      throws InvalidKeyException

  {

    engineInit(key, random);

  }

  private void reset()

  {

    result = null;

    last_phase_done = false;

  }

  private void checkState()

  {

    if (result == null || ! last_phase_done)

      throw new IllegalStateException("Not finished");

  }

}