package gnu.crypto.key.srp6;

// ----------------------------------------------------------------------------
// $Id: SRPAlgorithm.java,v 1.3 2005/10/06 04:24:16 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.sasl.srp.SRPRegistry;
import gnu.crypto.util.Prime;

import java.math.BigInteger;

/**
 * <p>Utilities for use with SRP-6 based methods and protocols.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 *    Thomas J. Wu.</li>
 * </ol>
 *
 * @version $Revision: 1.3 $
 */
public class SRPAlgorithm {

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

   // lifted from draft-burdis-cat-srp-sasl-09
   public static final BigInteger N_2048 = new BigInteger(
         "AC6BDB41324A9A9BF166DE5E1389582FAF72B6651987EE07FC3192943DB56050"+
         "A37329CBB4A099ED8193E0757767A13DD52312AB4B03310DCD7F48A9DA04FD50"+
         "E8083969EDB767B0CF6095179A163AB3661A05FBD5FAAAE82918A9962F0B93B8"+
         "55F97993EC975EEAA80D740ADBF4FF747359D041D5C33EA71D281E446B14773B"+
         "CA97B43A23FB801676BD207A436C6481F1D2B9078717461A5B9D32E688F87748"+
         "544523B524B0D57D5EA77A2775D2ECFA032CFBDBF52FB3786160279004E57AE6"+
         "AF874E7303CE53299CCC041C7BC308D82A5698F3A8D0C38271AE35F8E9DBFBB6"+
         "94B5C803D89F7AE435DE236D525F54759B65E372FCD68EF20FA7111F9E4AFF73",
         16);

   public static final BigInteger N_1536 = new BigInteger(
         "9DEF3CAFB939277AB1F12A8617A47BBBDBA51DF499AC4C80BEEEA9614B19CC4D"+
         "5F4F5F556E27CBDE51C6A94BE4607A291558903BA0D0F84380B655BB9A22E8DC"+
         "DF028A7CEC67F0D08134B1C8B97989149B609E0BE3BAB63D47548381DBC5B1FC"+
         "764E3F4B53DD9DA1158BFD3E2B9C8CF56EDF019539349627DB2FD53D24B7C486"+
         "65772E437D6C7F8CE442734AF7CCB7AE837C264AE3A9BEB87F8A2FE9B8B5292E"+
         "5A021FFF5E91479E8CE7A28C2442C6F315180F93499A234DCF76E3FED135F9BB",
         16);

   public static final BigInteger N_1280 = new BigInteger(
         "D77946826E811914B39401D56A0A7843A8E7575D738C672A090AB1187D690DC4"+
         "3872FC06A7B6A43F3B95BEAEC7DF04B9D242EBDC481111283216CE816E004B78"+
         "6C5FCE856780D41837D95AD787A50BBE90BD3A9C98AC0F5FC0DE744B1CDE1891"+
         "690894BC1F65E00DE15B4B2AA6D87100C9ECC2527E45EB849DEB14BB2049B163"+
         "EA04187FD27C1BD9C7958CD40CE7067A9C024F9B7C5A0B4F5003686161F0605B",
         16);

   public static final BigInteger N_1024 = new BigInteger(
         "EEAF0AB9ADB38DD69C33F80AFA8FC5E86072618775FF3C0B9EA2314C9C256576"+
         "D674DF7496EA81D3383B4813D692C6E0E0D5D8E250B98BE48E495C1D6089DAD1"+
         "5DC7D7B46154D6B6CE8EF4AD69B15D4982559B297BCF1885C529F566660E57EC"+
         "68EDBC3C05726CC02FD4CBF4976EAA9AFD5138FE8376435B9FC61D2FC0EB06E3",
         16);

   public static final BigInteger N_768 = new BigInteger(
         "B344C7C4F8C495031BB4E04FF8F84EE95008163940B9558276744D91F7CC9F40"+
         "2653BE7147F00F576B93754BCDDF71B636F2099E6FFF90E79575F3D0DE694AFF"+
         "737D9BE9713CEF8D837ADA6380B1093E94B6A529A8C6C2BE33E0867C60C3262B",
         16);

   public static final BigInteger N_640 = new BigInteger(
         "C94D67EB5B1A2346E8AB422FC6A0EDAEDA8C7F894C9EEEC42F9ED250FD7F0046"+
         "E5AF2CF73D6B2FA26BB08033DA4DE322E144E7A8E9B12A0E4637F6371F34A207"+
         "1C4B3836CBEEAB15034460FAA7ADF483",
         16);

   public static final BigInteger N_512 = new BigInteger(
         "D4C7F8A2B32C11B8FBA9581EC4BA4F1B04215642EF7355E37C0FC0443EF756EA"+
         "2C6B8EEB755A1C723027663CAA265EF785B8FF6A9B35227A52D86633DBDFCA43",
         16);

   public static final BigInteger N_384 = new BigInteger(
         "8025363296FB943FCE54BE717E0E2958A02A9672EF561953B2BAA3BAACC3ED57"+
         "54EB764C7AB7184578C57D5949CCB41B",
         16);

   public static final BigInteger N_264 = new BigInteger(
         "115B8B692E0E045692CF280B436735C77A5A9E8A9E7ED56C965F87DB5B2A2ECE3",
         16);

   private static final BigInteger ZERO = BigInteger.ZERO;
   private static final BigInteger ONE =  BigInteger.ONE;
   private static final BigInteger TWO =  BigInteger.valueOf(2L);

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

   /** Trivial constructor to enforce usage through class methods. */
   private SRPAlgorithm() {
      super();
   }

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

   public static void checkParams(final BigInteger N, final BigInteger g) {
      // 1. N should be at least 512-bit long
      final int blen = N.bitLength();
      if (blen < SRPRegistry.MINIMUM_MODULUS_BITLENGTH) {
         throw new IllegalArgumentException("Bit length of N ("
               +blen+") is too low. Should be at least "
               +SRPRegistry.MINIMUM_MODULUS_BITLENGTH);
      }
      // 2. N should be a prime
      if (!Prime.passEulerCriterion(N)) {
         throw new IllegalArgumentException("N should be prime but isn't");
      }
      // 3. N should be of the form 2*q + 1, where q is prime
      final BigInteger q = N.subtract(ONE).divide(TWO);
      if (!Prime.passEulerCriterion(q)) {
         throw new IllegalArgumentException("(N-1)/2 should be prime but isn't");
      }
      // 4. g**q should be -1 mod N
      final BigInteger gq = g.modPow(q, N).add(ONE).mod(N);
      if (gq.compareTo(ZERO) != 0) {
         throw new IllegalArgumentException("g**q should be -1 (mod N) but isn't");
      }
   }

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