/* 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.

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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
executable, regardless of the license terms of these independent
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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;

/**
 * <p>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.</p>
 */
public final class SRP
{

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

  /** 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;

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

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

    this.mda = mda;
  }

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

  /**
   * <p>Returns an instance of this object that uses the designated message
   * digest algorithm as its digest function.</p>
   *
   * @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;
  }

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

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

  // Message Digest algorithm related methods --------------------------------

  /**
   * <p>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.</p>
   *
   * @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();
  }

  /**
   * <p>Convenience method to return the result of digesting the designated
   * input with a new instance of the SRP message digest algorithm.</p>
   *
   * @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();
  }

  /**
   * <p>Convenience method to return the result of digesting the designated
   * input with a new instance of the SRP message digest algorithm.</p>
   *
   * @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"));
  }

  // Other methods -----------------------------------------------------------

  /**
   * <p>Convenience method to XOR N bytes from two arrays; N being the output
   * size of the SRP message digest algorithm.</p>
   *
   * @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();
  }
}