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jeremybenn |
/* SRP6KeyAgreement.java --
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Copyright (C) 2003, 2006 Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.javax.crypto.key.srp6;
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import gnu.java.security.Registry;
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import gnu.java.security.hash.IMessageDigest;
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import gnu.java.security.util.Util;
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import gnu.javax.crypto.key.BaseKeyAgreementParty;
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import gnu.javax.crypto.key.KeyAgreementException;
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import gnu.javax.crypto.sasl.srp.SRP;
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import java.math.BigInteger;
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/**
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* The Secure Remote Password (SRP) key agreement protocol, also known as SRP-6,
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* is designed by Thomas J. Wu (see references). The protocol, and its elements
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* are described as follows:
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* <pre>
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* N A large safe prime (N = 2q+1, where q is prime)
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* All arithmetic is done modulo N.
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* g A generator modulo N
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* s User's salt
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* I Username
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* p Cleartext Password
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* H() One-way hash function
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* ˆ (Modular) Exponentiation
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* u Random scrambling parameter
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* a,b Secret ephemeral values
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* A,B Public ephemeral values
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* x Private key (derived from p and s)
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* v Password verifier
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*
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* The host stores passwords using the following formula:
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* x = H(s | H(I ":" p)) (s is chosen randomly)
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* v = gˆx (computes password verifier)
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*
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* The host then keeps {I, s, v} in its password database.
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*
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* The authentication protocol itself goes as follows:
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* User -> Host: I, A = gˆa (identifies self, a = random number)
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* Host -> User: s, B = 3v + gˆb (sends salt, b = random number)
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*
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* Both: u = H(A, B)
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*
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* User: x = H(s, p) (user enters password)
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* User: S = (B - 3gˆx) ˆ (a + ux) (computes session key)
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* User: K = H(S)
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*
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* Host: S = (Avˆu) ˆ b (computes session key)
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* Host: K = H(S)
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* </pre>
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* <p>
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* Reference:
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* <ol>
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* <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
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* Thomas J. Wu.</li>
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* </ol>
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*/
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public abstract class SRP6KeyAgreement
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extends BaseKeyAgreementParty
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{
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public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.srp6.ka.prng";
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public static final String SHARED_MODULUS = "gnu.crypto.srp6.ka.N";
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public static final String GENERATOR = "gnu.crypto.srp6.ka.g";
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public static final String HASH_FUNCTION = "gnu.crypto.srp6.ka.H";
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public static final String USER_IDENTITY = "gnu.crypto.srp6.ka.I";
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public static final String USER_PASSWORD = "gnu.crypto.srp6.ka.p";
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public static final String HOST_PASSWORD_DB = "gnu.crypto.srp6.ka.password.db";
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protected static final BigInteger THREE = BigInteger.valueOf(3L);
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protected SRP srp;
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protected BigInteger N;
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protected BigInteger g;
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/** The shared secret key. */
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protected BigInteger K;
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protected SRP6KeyAgreement()
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{
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super(Registry.SRP6_KA);
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}
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protected byte[] engineSharedSecret() throws KeyAgreementException
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{
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return Util.trim(K);
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}
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protected void engineReset()
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{
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srp = null;
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N = null;
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g = null;
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K = null;
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}
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protected BigInteger uValue(final BigInteger A, final BigInteger B)
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{
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final IMessageDigest hash = srp.newDigest();
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byte[] b;
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b = Util.trim(A);
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hash.update(b, 0, b.length);
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b = Util.trim(B);
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hash.update(b, 0, b.length);
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return new BigInteger(1, hash.digest());
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}
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}
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