package gnu.crypto.sasl.srp;

// ----------------------------------------------------------------------------
// $Id: SRP.java,v 1.6 2005/10/06 04:24:18 rsdio Exp $
//
// Copyright (C) 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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 Crypto 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 this program; 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.
// ----------------------------------------------------------------------------

import gnu.crypto.hash.HashFactory;
import gnu.crypto.hash.IMessageDigest;
import gnu.crypto.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>
 *
 * @version $Revision: 1.6 $
 */
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();
   }
}
