path: root/gnu/javax/crypto/key/srp6/SRPKeyPairGenerator.java

/* SRPKeyPairGenerator.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
the Free Software Foundation; either version 2 of the License, 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; if not, write to the Free Software
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
conditions of the GNU General Public License cover the whole
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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
executable, regardless of the license terms of these independent
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package gnu.javax.crypto.key.srp6;

import gnu.java.security.Configuration;
import gnu.java.security.Registry;
import gnu.java.security.key.IKeyPairGenerator;
import gnu.java.security.util.PRNG;

import java.math.BigInteger;
import java.security.KeyPair;
import java.security.SecureRandom;
import java.util.Map;
import java.util.logging.Logger;

/**
 * Reference:
 * <ol>
 * <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 * Thomas J. Wu.</li>
 * </ol>
 */
public class SRPKeyPairGenerator
    implements IKeyPairGenerator
{
  private static final Logger log = Logger.getLogger(SRPKeyPairGenerator.class.getName());
  private static final BigInteger ZERO = BigInteger.ZERO;
  private static final BigInteger ONE = BigInteger.ONE;
  private static final BigInteger TWO = BigInteger.valueOf(2L);
  private static final BigInteger THREE = BigInteger.valueOf(3L);
  /** Property name of the length (Integer) of the modulus (N) of an SRP key. */
  public static final String MODULUS_LENGTH = "gnu.crypto.srp.L";
  /** Property name of the Boolean indicating wether or not to use defaults. */
  public static final String USE_DEFAULTS = "gnu.crypto.srp.use.defaults";
  /** Property name of the modulus (N) of an SRP key. */
  public static final String SHARED_MODULUS = "gnu.crypto.srp.N";
  /** Property name of the generator (g) of an SRP key. */
  public static final String GENERATOR = "gnu.crypto.srp.g";
  /** Property name of the user's verifier (v) for a Server SRP key. */
  public static final String USER_VERIFIER = "gnu.crypto.srp.v";
  /**
   * 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.srp.prng";
  /** Default value for the modulus length. */
  private static final int DEFAULT_MODULUS_LENGTH = 1024;
  /** The optional {@link SecureRandom} instance to use. */
  private SecureRandom rnd = null;
  /** Bit length of the shared modulus. */
  private int l;
  /** The shared public modulus. */
  private BigInteger N;
  /** The Field generator. */
  private BigInteger g;
  /** The user's verifier MPI. */
  private BigInteger v;
  /** Our default source of randomness. */
  private PRNG prng = null;

  // implicit 0-arguments constructor

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

  public void setup(Map attributes)
  {
    // do we have a SecureRandom, or should we use our own?
    rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
    N = (BigInteger) attributes.get(SHARED_MODULUS);
    if (N != null)
      {
        l = N.bitLength();
        g = (BigInteger) attributes.get(GENERATOR);
        if (g == null)
          g = TWO;
        SRPAlgorithm.checkParams(N, g);
      }
    else
      { // generate or use default values for N and g
        Boolean useDefaults = (Boolean) attributes.get(USE_DEFAULTS);
        if (useDefaults == null)
          useDefaults = Boolean.TRUE;
        Integer L = (Integer) attributes.get(MODULUS_LENGTH);
        l = DEFAULT_MODULUS_LENGTH;
        if (useDefaults.equals(Boolean.TRUE))
          {
            if (L != null)
              {
                l = L.intValue();
                switch (l)
                  {
                  case 512:
                    N = SRPAlgorithm.N_512;
                    break;
                  case 640:
                    N = SRPAlgorithm.N_640;
                    break;
                  case 768:
                    N = SRPAlgorithm.N_768;
                    break;
                  case 1024:
                    N = SRPAlgorithm.N_1024;
                    break;
                  case 1280:
                    N = SRPAlgorithm.N_1280;
                    break;
                  case 1536:
                    N = SRPAlgorithm.N_1536;
                    break;
                  case 2048:
                    N = SRPAlgorithm.N_2048;
                    break;
                  default:
                    throw new IllegalArgumentException(
                        "unknown default shared modulus bit length");
                  }
                g = TWO;
                l = N.bitLength();
              }
          }
        else // generate new N and g
          {
            if (L != null)
              {
                l = L.intValue();
                if ((l % 256) != 0 || l < 512 || l > 2048)
                  throw new IllegalArgumentException(
                      "invalid shared modulus bit length");
              }
          }
      }
    // are we using this generator on the server side, or the client side?
    v = (BigInteger) attributes.get(USER_VERIFIER);
  }

  public KeyPair generate()
  {
    if (N == null)
      {
        BigInteger[] params = generateParameters();
        BigInteger q = params[0];
        N = params[1];
        g = params[2];
        if (Configuration.DEBUG)
          {
            log.fine("q: " + q.toString(16));
            log.fine("N: " + N.toString(16));
            log.fine("g: " + g.toString(16));
          }
      }
    return (v != null ? hostKeyPair() : userKeyPair());
  }

  private synchronized BigInteger[] generateParameters()
  {
    // N A large safe prime (N = 2q+1, where q is prime)
    // g A generator modulo N
    BigInteger q, p, g;
    byte[] qBytes = new byte[l / 8];
    do
      {
        do
          {
            nextRandomBytes(qBytes);
            q = new BigInteger(1, qBytes);
            q = q.setBit(0).setBit(l - 2).clearBit(l - 1);
          }
        while (! q.isProbablePrime(80));
        p = q.multiply(TWO).add(ONE);
      }
    while (p.bitLength() != l || ! p.isProbablePrime(80));
    // compute g. from FIPS-186, Appendix 4: e == 2
    BigInteger p_minus_1 = p.subtract(ONE);
    g = TWO;
    // Set h = any integer, where 1 < h < p - 1 and
    // h differs from any value previously tried
    for (BigInteger h = TWO; h.compareTo(p_minus_1) < 0; h = h.add(ONE))
      {
        // Set g = h**2 mod p
        g = h.modPow(TWO, p);
        // If g = 1, go to step 3
        if (! g.equals(ONE))
          break;
      }
    return new BigInteger[] { q, p, g };
  }

  private KeyPair hostKeyPair()
  {
    byte[] bBytes = new byte[(l + 7) / 8];
    BigInteger b, B;
    do
      {
        do
          {
            nextRandomBytes(bBytes);
            b = new BigInteger(1, bBytes);
          }
        while (b.compareTo(ONE) <= 0 || b.compareTo(N) >= 0);
        B = THREE.multiply(v).add(g.modPow(b, N)).mod(N);
      }
    while (B.compareTo(ZERO) == 0 || B.compareTo(N) >= 0);
    KeyPair result = new KeyPair(new SRPPublicKey(new BigInteger[] { N, g, B }),
                                 new SRPPrivateKey(new BigInteger[] { N, g, b, v }));
    return result;
  }

  private KeyPair userKeyPair()
  {
    byte[] aBytes = new byte[(l + 7) / 8];
    BigInteger a, A;
    do
      {
        do
          {
            nextRandomBytes(aBytes);
            a = new BigInteger(1, aBytes);
          }
        while (a.compareTo(ONE) <= 0 || a.compareTo(N) >= 0);
        A = g.modPow(a, N);
      }
    while (A.compareTo(ZERO) == 0 || A.compareTo(N) >= 0);
    KeyPair result = new KeyPair(new SRPPublicKey(new BigInteger[] { N, g, A }),
                                 new SRPPrivateKey(new BigInteger[] { N, g, a }));
    return result;
  }

  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;
  }
}