/* SRP.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
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
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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
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package gnu.javax.crypto.sasl.srp;

import gnu.java.security.hash.HashFactory;
import gnu.java.security.hash.IMessageDigest;
import gnu.java.security.util.Util;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.util.HashMap;

/**
 * A Factory class that returns SRP Singletons that know all SRP-related
 * mathematical computations and protocol-related operations for both the
 * client- and server-sides.
 */
public final class SRP
{
  /** The map of already instantiated SRP algorithm instances. */
  private static final HashMap algorithms = new HashMap();
  private static final byte COLON = (byte) 0x3A;
  /** The underlying message digest algorithm used for all SRP calculations. */
  private IMessageDigest mda;

  /** Trivial private constructor to enforce Singleton pattern. */
  private SRP(final IMessageDigest mda)
  {
    super();

    this.mda = mda;
  }

  /**
   * Returns an instance of this object that uses the designated message digest
   * algorithm as its digest function.
   * 
   * @return an instance of this object for the designated digest name.
   */
  public static synchronized SRP instance(String mdName)
  {
    if (mdName != null)
      mdName = mdName.trim().toLowerCase();
    if (mdName == null || mdName.equals(""))
      mdName = SRPRegistry.SRP_DEFAULT_DIGEST_NAME;
    SRP result = (SRP) algorithms.get(mdName);
    if (result == null)
      {
        final IMessageDigest mda = HashFactory.getInstance(mdName);
        result = new SRP(mda);
        algorithms.put(mdName, result);
      }
    return result;
  }

  private static final byte[] xor(final byte[] b1, final byte[] b2,
                                  final int length)
  {
    final byte[] result = new byte[length];
    for (int i = 0; i < length; ++i)
      result[i] = (byte)(b1[i] ^ b2[i]);
    return result;
  }

  /** @return the message digest algorithm name used by this instance. */
  public String getAlgorithm()
  {
    return mda.name();
  }

  /**
   * Returns a new instance of the SRP message digest algorithm --which is
   * SHA-160 by default, but could be anything else provided the proper
   * conditions as specified in the SRP specifications.
   * 
   * @return a new instance of the underlying SRP message digest algorithm.
   * @throws RuntimeException if the implementation of the message digest
   *           algorithm does not support cloning.
   */
  public IMessageDigest newDigest()
  {
    return (IMessageDigest) mda.clone();
  }

  /**
   * Convenience method to return the result of digesting the designated input
   * with a new instance of the SRP message digest algorithm.
   * 
   * @param src some bytes to digest.
   * @return the bytes constituting the result of digesting the designated input
   *         with a new instance of the SRP message digest algorithm.
   */
  public byte[] digest(final byte[] src)
  {
    final IMessageDigest hash = (IMessageDigest) mda.clone();
    hash.update(src, 0, src.length);
    return hash.digest();
  }

  /**
   * Convenience method to return the result of digesting the designated input
   * with a new instance of the SRP message digest algorithm.
   * 
   * @param src a String whose bytes (using US-ASCII encoding) are to be
   *          digested.
   * @return the bytes constituting the result of digesting the designated input
   *         with a new instance of the SRP message digest algorithm.
   * @throws UnsupportedEncodingException if US-ASCII charset is not found.
   */
  public byte[] digest(final String src) throws UnsupportedEncodingException
  {
    return digest(src.getBytes("US-ASCII"));
  }

  /**
   * Convenience method to XOR N bytes from two arrays; N being the output size
   * of the SRP message digest algorithm.
   * 
   * @param a the first byte array.
   * @param b the second one.
   * @return N bytes which are the result of the XOR operations on the first N
   *         bytes from the designated arrays. N is the size of the SRP message
   *         digest algorithm; eg. 20 for SHA-160.
   */
  public byte[] xor(final byte[] a, final byte[] b)
  {
    return xor(a, b, mda.hashSize());
  }

  public byte[] generateM1(final BigInteger N, final BigInteger g,
                           final String U, final byte[] s, final BigInteger A,
                           final BigInteger B, final byte[] K, final String I,
                           final String L, final byte[] cn, final byte[] cCB)
      throws UnsupportedEncodingException
  {
    final IMessageDigest hash = (IMessageDigest) mda.clone();
    byte[] b;
    b = xor(digest(Util.trim(N)), digest(Util.trim(g)));
    hash.update(b, 0, b.length);
    b = digest(U);
    hash.update(b, 0, b.length);
    hash.update(s, 0, s.length);
    b = Util.trim(A);
    hash.update(b, 0, b.length);
    b = Util.trim(B);
    hash.update(b, 0, b.length);
    hash.update(K, 0, K.length);
    b = digest(I);
    hash.update(b, 0, b.length);
    b = digest(L);
    hash.update(b, 0, b.length);
    hash.update(cn, 0, cn.length);
    hash.update(cCB, 0, cCB.length);
    return hash.digest();
  }

  public byte[] generateM2(final BigInteger A, final byte[] M1, final byte[] K,
                           final String U, final String I, final String o,
                           final byte[] sid, final int ttl, final byte[] cIV,
                           final byte[] sIV, final byte[] sCB)
      throws UnsupportedEncodingException
  {
    final IMessageDigest hash = (IMessageDigest) mda.clone();
    byte[] b;
    b = Util.trim(A);
    hash.update(b, 0, b.length);
    hash.update(M1, 0, M1.length);
    hash.update(K, 0, K.length);
    b = digest(U);
    hash.update(b, 0, b.length);
    b = digest(I);
    hash.update(b, 0, b.length);
    b = digest(o);
    hash.update(b, 0, b.length);
    hash.update(sid, 0, sid.length);
    hash.update((byte)(ttl >>> 24));
    hash.update((byte)(ttl >>> 16));
    hash.update((byte)(ttl >>> 8));
    hash.update((byte) ttl);
    hash.update(cIV, 0, cIV.length);
    hash.update(sIV, 0, sIV.length);
    hash.update(sCB, 0, sCB.length);
    return hash.digest();
  }

  public byte[] generateKn(final byte[] K, final byte[] cn, final byte[] sn)
  {
    final IMessageDigest hash = (IMessageDigest) mda.clone();
    hash.update(K, 0, K.length);
    hash.update(cn, 0, cn.length);
    hash.update(sn, 0, sn.length);
    return hash.digest();
  }

  public byte[] computeX(final byte[] s, final String user,
                         final String password)
      throws UnsupportedEncodingException
  {
    return computeX(s, user.getBytes("US-ASCII"), password.getBytes("US-ASCII"));
  }

  public byte[] computeX(final byte[] s, final String user, final byte[] p)
      throws UnsupportedEncodingException
  {
    return computeX(s, user.getBytes("US-ASCII"), p);
  }

  private byte[] computeX(final byte[] s, final byte[] user, final byte[] p)
  {
    final IMessageDigest hash = (IMessageDigest) mda.clone();
    hash.update(user, 0, user.length);
    hash.update(COLON);
    hash.update(p, 0, p.length);
    final byte[] up = hash.digest();
    hash.update(s, 0, s.length);
    hash.update(up, 0, up.length);
    return hash.digest();
  }
}