path: root/gnu/javax/crypto/key/dh/GnuDHKeyPairGenerator.java

/* GnuDHKeyPairGenerator.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a 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
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your option) any later version.

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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.

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Foundation, Inc., 51 Franklin St, 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
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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package gnu.javax.crypto.key.dh;

import gnu.java.security.Registry;
import gnu.java.security.hash.Sha160;
import gnu.java.security.key.IKeyPairGenerator;
import gnu.java.security.util.PRNG;

import java.io.PrintWriter;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.util.Map;

import javax.crypto.spec.DHGenParameterSpec;

/**
 * <p>An implementation of a Diffie-Hellman keypair generator.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://www.ietf.org/rfc/rfc2631.txt">Diffie-Hellman Key
 *    Agreement Method</a><br>
 *    Eric Rescorla.</li>
 * </ol>
 */
public class GnuDHKeyPairGenerator implements IKeyPairGenerator
{

  // Debugging methods and variables
  // -------------------------------------------------------------------------

  private static final String NAME = "dh";

  private static final boolean DEBUG = false;

  private static final int debuglevel = 5;

  private static final PrintWriter err = new PrintWriter(System.out, true);

  private static void debug(String s)
  {
    err.println(">>> " + NAME + ": " + s);
  }

  // Constants and variables
  // -------------------------------------------------------------------------

  /**
   * Property name of an optional {@link SecureRandom} instance to use. The
   * default is to use a classloader singleton from {@link PRNG}.
   */
  public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.dh.prng";

  /**
   * Property name of an optional {@link DHGenParameterSpec} instance to use
   * for this generator.
   */
  public static final String DH_PARAMETERS = "gnu.crypto.dh.params";

  /** Property name of the size in bits (Integer) of the public prime (p). */
  public static final String PRIME_SIZE = "gnu.crypto.dh.L";

  /** Property name of the size in bits (Integer) of the private exponent (x). */
  public static final String EXPONENT_SIZE = "gnu.crypto.dh.m";

  /** Default value for the size in bits of the public prime (p). */
  //   private static final int DEFAULT_PRIME_SIZE = 1024;
  private static final int DEFAULT_PRIME_SIZE = 512;

  /** Default value for the size in bits of the private exponent (x). */
  private static final int DEFAULT_EXPONENT_SIZE = 160;

  /** The SHA instance to use. */
  private Sha160 sha = new Sha160();

  /** The optional {@link SecureRandom} instance to use. */
  private SecureRandom rnd = null;

  /** The desired size in bits of the public prime (p). */
  private int l;

  /** The desired size in bits of the private exponent (x). */
  private int m;

  private BigInteger seed;

  private BigInteger counter;

  private BigInteger q;

  private BigInteger p;

  private BigInteger j;

  private BigInteger g;

  /** Our default source of randomness. */
  private PRNG prng = null;

  // Constructor(s)
  // -------------------------------------------------------------------------

  // default 0-arguments constructor

  // Class methods
  // -------------------------------------------------------------------------

  // Instance methods
  // -------------------------------------------------------------------------

  // gnu.crypto.keys.IKeyPairGenerator interface implementation ---------------

  public String name()
  {
    return Registry.DH_KPG;
  }

  public void setup(Map attributes)
  {
    // do we have a SecureRandom, or should we use our own?
    rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);

    // are we given a set of Diffie-Hellman generation parameters or we shall
    // use our own?
    DHGenParameterSpec params = (DHGenParameterSpec) attributes.get(DH_PARAMETERS);

    // find out the desired sizes
    if (params != null)
      {
        l = params.getPrimeSize();
        m = params.getExponentSize();
      }
    else
      {
        Integer bi = (Integer) attributes.get(PRIME_SIZE);
        l = (bi == null ? DEFAULT_PRIME_SIZE : bi.intValue());
        bi = (Integer) attributes.get(EXPONENT_SIZE);
        m = (bi == null ? DEFAULT_EXPONENT_SIZE : bi.intValue());
      }

    //      if ((L % 256) != 0 || L < 1024) {
    if ((l % 256) != 0 || l < DEFAULT_PRIME_SIZE)
      {
        throw new IllegalArgumentException("invalid modulus size");
      }
    if ((m % 8) != 0 || m < DEFAULT_EXPONENT_SIZE)
      {
        throw new IllegalArgumentException("invalid exponent size");
      }
    if (m > l)
      {
        throw new IllegalArgumentException("exponent size > modulus size");
      }
  }

  public KeyPair generate()
  {
    if (p == null)
      {
        BigInteger[] params = new RFC2631(m, l, rnd).generateParameters();
        seed = params[RFC2631.DH_PARAMS_SEED];
        counter = params[RFC2631.DH_PARAMS_COUNTER];
        q = params[RFC2631.DH_PARAMS_Q];
        p = params[RFC2631.DH_PARAMS_P];
        j = params[RFC2631.DH_PARAMS_J];
        g = params[RFC2631.DH_PARAMS_G];
        if (DEBUG && debuglevel > 0)
          {
            debug("seed: 0x" + seed.toString(16));
            debug("counter: " + counter.intValue());
            debug("q: 0x" + q.toString(16));
            debug("p: 0x" + p.toString(16));
            debug("j: 0x" + j.toString(16));
            debug("g: 0x" + g.toString(16));
          }
      }

    // generate a private number x of length m such as: 1 < x < q - 1
    BigInteger q_minus_1 = q.subtract(BigInteger.ONE);
    byte[] mag = new byte[(m + 7) / 8];
    BigInteger x;
    while (true)
      {
        nextRandomBytes(mag);
        x = new BigInteger(1, mag);
        if (x.bitLength() == m && x.compareTo(BigInteger.ONE) > 0
            && x.compareTo(q_minus_1) < 0)
          {
            break;
          }
      }
    BigInteger y = g.modPow(x, p);

    PrivateKey secK = new GnuDHPrivateKey(q, p, g, x);
    PublicKey pubK = new GnuDHPublicKey(q, p, g, y);

    return new KeyPair(pubK, secK);
  }

  // other methods -----------------------------------------------------------

  /**
   * <p>Fills the designated byte array with random data.</p>
   *
   * @param buffer the byte array to fill with random data.
   */
  private void nextRandomBytes(byte[] buffer)
  {
    if (rnd != null)
      {
        rnd.nextBytes(buffer);
      }
    else
      getDefaultPRNG().nextBytes(buffer);
  }

  private PRNG getDefaultPRNG()
  {
    if (prng == null)
      prng = PRNG.getInstance();

    return prng;
  }
}