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1: /* SRP6KeyAgreement.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.srp6; 40: 41: import gnu.java.security.Registry; 42: import gnu.java.security.hash.IMessageDigest; 43: import gnu.java.security.util.Util; 44: 45: import gnu.javax.crypto.key.BaseKeyAgreementParty; 46: import gnu.javax.crypto.key.KeyAgreementException; 47: import gnu.javax.crypto.sasl.srp.SRP; 48: 49: import java.math.BigInteger; 50: 51: /** 52: * The Secure Remote Password (SRP) key agreement protocol, also known as SRP-6, 53: * is designed by Thomas J. Wu (see references). The protocol, and its elements 54: * are described as follows: 55: * <pre> 56: * N A large safe prime (N = 2q+1, where q is prime) 57: * All arithmetic is done modulo N. 58: * g A generator modulo N 59: * s User's salt 60: * I Username 61: * p Cleartext Password 62: * H() One-way hash function 63: * ˆ (Modular) Exponentiation 64: * u Random scrambling parameter 65: * a,b Secret ephemeral values 66: * A,B Public ephemeral values 67: * x Private key (derived from p and s) 68: * v Password verifier 69: * 70: * The host stores passwords using the following formula: 71: * x = H(s | H(I ":" p)) (s is chosen randomly) 72: * v = gˆx (computes password verifier) 73: * 74: * The host then keeps {I, s, v} in its password database. 75: * 76: * The authentication protocol itself goes as follows: 77: * User -> Host: I, A = gˆa (identifies self, a = random number) 78: * Host -> User: s, B = 3v + gˆb (sends salt, b = random number) 79: * 80: * Both: u = H(A, B) 81: * 82: * User: x = H(s, p) (user enters password) 83: * User: S = (B - 3gˆx) ˆ (a + ux) (computes session key) 84: * User: K = H(S) 85: * 86: * Host: S = (Avˆu) ˆ b (computes session key) 87: * Host: K = H(S) 88: * </pre> 89: * <p> 90: * Reference: 91: * <ol> 92: * <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br> 93: * Thomas J. Wu.</li> 94: * </ol> 95: */ 96: public abstract class SRP6KeyAgreement 97: extends BaseKeyAgreementParty 98: { 99: public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.srp6.ka.prng"; 100: public static final String SHARED_MODULUS = "gnu.crypto.srp6.ka.N"; 101: public static final String GENERATOR = "gnu.crypto.srp6.ka.g"; 102: public static final String HASH_FUNCTION = "gnu.crypto.srp6.ka.H"; 103: public static final String USER_IDENTITY = "gnu.crypto.srp6.ka.I"; 104: public static final String USER_PASSWORD = "gnu.crypto.srp6.ka.p"; 105: public static final String HOST_PASSWORD_DB = "gnu.crypto.srp6.ka.password.db"; 106: protected static final BigInteger THREE = BigInteger.valueOf(3L); 107: protected SRP srp; 108: protected BigInteger N; 109: protected BigInteger g; 110: /** The shared secret key. */ 111: protected BigInteger K; 112: 113: protected SRP6KeyAgreement() 114: { 115: super(Registry.SRP6_KA); 116: } 117: 118: protected byte[] engineSharedSecret() throws KeyAgreementException 119: { 120: return Util.trim(K); 121: } 122: 123: protected void engineReset() 124: { 125: srp = null; 126: N = null; 127: g = null; 128: K = null; 129: } 130: 131: protected BigInteger uValue(final BigInteger A, final BigInteger B) 132: { 133: final IMessageDigest hash = srp.newDigest(); 134: byte[] b; 135: b = Util.trim(A); 136: hash.update(b, 0, b.length); 137: b = Util.trim(B); 138: hash.update(b, 0, b.length); 139: return new BigInteger(1, hash.digest()); 140: } 141: }