libjava/classpath/gnu/javax/crypto/key/dh/DiffieHellmanKeyAgreement.java

   1 /* DiffieHellmanKeyAgreement.java --
   2    Copyright (C) 2003, 2006 Free Software Foundation, Inc.
   3
   4 This file is a part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or (at
   9 your option) any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19 USA
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version.  */
  37
  38
  39 package gnu.javax.crypto.key.dh;
  40
  41 import gnu.java.security.Registry;
  42 import gnu.java.security.util.Util;
  43
  44 import gnu.javax.crypto.key.BaseKeyAgreementParty;
  45 import gnu.javax.crypto.key.KeyAgreementException;
  46
  47 import java.math.BigInteger;
  48
  49 import javax.crypto.interfaces.DHPrivateKey;
  50
  51 /**
  52  * <p>The basic version of the Diffie-Hellman key agreement is described in the
  53  * Handbook of Applied Cryptography [HAC] as follows:</p>
  54  * <ul>
  55  *    <li>An appropriate prime p and generator g of Z<sub>p</sub><sup>*</sup>
  56  *    (2 &lt;= g &lt;= p-2) are selected and published.</li>
  57  *    <li>A and B each send the other one message over an open channel; as a
  58  *    result, they both can then compute a shared secret key K which they can
  59  *    use to protect their future communication.</li>
  60  *    <li>A chooses a random secret x, 1 &lt;= x &lt;= p-2, and sends B message
  61  *    (1) which is g^x mod p.</li>
  62  *    <li>B chooses a random secret y, 1 &lt;= y &lt;= p-2, and sends A message
  63  *    (2) which is g^y mod p.</li>
  64  *    <li>B receives message (1) and computes the shared key as K = (g^x)^y mod
  65  *    p.</li>
  66  *    <li>A receives message (2) and computes the shared key as K = (g^y)^x mod
  67  *    p.</li>
  68  * </ul>
  69  *
  70  * <p>RFC-2631 describes a <i>Static-Static Mode</i> of operations with
  71  * Diffie-Hellman keypairs as follows:</p>
  72  * <pre>
  73  * "In Static-Static mode, both the sender and the recipient have a
  74  static (and certified) key pair. Since the sender's and recipient's
  75  keys are therefore the same for each message, ZZ will be the same for
  76  each message. Thus, partyAInfo MUST be used (and different for each
  77  message) in order to ensure that different messages use different
  78  KEKs. Implementations MAY implement Static-Static mode."
  79  * </pre>
  80  *
  81  * <p>Reference:</p>
  82  * <ol>
  83  *    <li><a href="http://www.ietf.org/rfc/rfc2631.txt">Diffie-Hellman Key
  84  *    Agreement Method</a><br>
  85  *    Eric Rescorla.</li>
  86  *    <li><a href="http://www.cacr.math.uwaterloo.ca/hac">[HAC]</a>: Handbook of
  87  *    Applied Cryptography.<br>
  88  *    CRC Press, Inc. ISBN 0-8493-8523-7, 1997<br>
  89  *    Menezes, A., van Oorschot, P. and S. Vanstone.</li>
  90  * </ol>
  91  */
  92 public abstract class DiffieHellmanKeyAgreement extends BaseKeyAgreementParty
  93 {
  94
  95   // Constants and variables
  96   // -------------------------------------------------------------------------
  97
  98   public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.dh.ka.prng";
  99
 100   public static final String KA_DIFFIE_HELLMAN_OWNER_PRIVATE_KEY = "gnu.crypto.dh.ka.owner.private.key";
 101
 102   /** The key agreement party's private key. */
 103   protected DHPrivateKey ownerKey;
 104
 105   /** The shared secret key. */
 106   protected BigInteger ZZ;
 107
 108   // Constructor(s)
 109   // -------------------------------------------------------------------------
 110
 111   protected DiffieHellmanKeyAgreement()
 112   {
 113     super(Registry.DH_KA);
 114   }
 115
 116   // Class methods
 117   // -------------------------------------------------------------------------
 118
 119   // Instance methods
 120   // -------------------------------------------------------------------------
 121
 122   // implementation of common abstract methods in BaseKeyAGreementParty ------
 123
 124   protected byte[] engineSharedSecret() throws KeyAgreementException
 125   {
 126     return Util.trim(ZZ);
 127   }
 128
 129   protected void engineReset()
 130   {
 131     ownerKey = null;
 132     ZZ = null;
 133   }
 134 }