/* * Copyright (c) 1996, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */  package sun.security.ssl; import java.math.BigInteger;import java.security.*; import javax.crypto.SecretKey;import javax.crypto.KeyAgreement;import javax.crypto.interfaces.DHPublicKey;import javax.crypto.spec.*; /** * This class implements the Diffie-Hellman key exchange algorithm. * D-H means combining your private key with your partners public key to * generate a number. The peer does the same with its private key and our * public key. Through the magic of Diffie-Hellman we both come up with the * same number. This number is secret (discounting MITM attacks) and hence * called the shared secret. It has the same length as the modulus, e.g. 512 * or 1024 bit. Man-in-the-middle attacks are typically countered by an * independent authentication step using certificates (RSA, DSA, etc.). * * The thing to note is that the shared secret is constant for two partners * with constant private keys. This is often not what we want, which is why * it is generally a good idea to create a new private key for each session. * Generating a private key involves one modular exponentiation assuming * suitable D-H parameters are available. * * General usage of this class (TLS DHE case): *  . if we are server, call DHCrypt(keyLength,random). This generates *    an ephemeral keypair of the request length. *  . if we are client, call DHCrypt(modulus, base, random). This *    generates an ephemeral keypair using the parameters specified by the server. *  . send parameters and public value to remote peer *  . receive peers ephemeral public key *  . call getAgreedSecret() to calculate the shared secret * * In TLS the server chooses the parameter values itself, the client must use * those sent to it by the server. * * The use of ephemeral keys as described above also achieves what is called * "forward secrecy". This means that even if the authentication keys are * broken at a later date, the shared secret remains secure. The session is * compromised only if the authentication keys are already broken at the * time the key exchange takes place and an active MITM attack is used. * This is in contrast to straightforward encrypting RSA key exchanges. * * @author David Brownell */final class DHCrypt {     // group parameters (prime modulus and generator)    private BigInteger modulus;                 // P (aka N)    private BigInteger base;                    // G (aka alpha)     // our private key (including private component x)    private PrivateKey privateKey;     // public component of our key, X = (g ^ x) mod p    private BigInteger publicValue;             // X (aka y)     /**     * Generate a Diffie-Hellman keypair of the specified size.     */    DHCrypt(int keyLength, SecureRandom random) {        try {            KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman");            kpg.initialize(keyLength, random);            KeyPair kp = kpg.generateKeyPair();            privateKey = kp.getPrivate();            DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic());            publicValue = spec.getY();            modulus = spec.getP();            base = spec.getG();        } catch (GeneralSecurityException e) {            throw new RuntimeException("Could not generate DH keypair", e);        }    }      /**     * Generate a Diffie-Hellman keypair using the specified parameters.     *     * @param modulus the Diffie-Hellman modulus P     * @param base the Diffie-Hellman base G     */    DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) {        this.modulus = modulus;        this.base = base;        try {            KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman");            DHParameterSpec params = new DHParameterSpec(modulus, base);            kpg.initialize(params, random);            KeyPair kp = kpg.generateKeyPair();            privateKey = kp.getPrivate();            DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic());            publicValue = spec.getY();        } catch (GeneralSecurityException e) {            throw new RuntimeException("Could not generate DH keypair", e);        }    }     static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) {        if (key instanceof DHPublicKey) {            DHPublicKey dhKey = (DHPublicKey)key;            DHParameterSpec params = dhKey.getParams();            return new DHPublicKeySpec(dhKey.getY(), params.getP(), params.getG());        }        try {            KeyFactory factory = JsseJce.getKeyFactory("DH");            return factory.getKeySpec(key, DHPublicKeySpec.class);        } catch (Exception e) {            throw new RuntimeException(e);        }    }      /** Returns the Diffie-Hellman modulus. */    BigInteger getModulus() {        return modulus;    }     /** Returns the Diffie-Hellman base (generator).  */    BigInteger getBase() {        return base;    }     /**     * Gets the public key of this end of the key exchange.     */    BigInteger getPublicKey() {        return publicValue;    }     /**     * Get the secret data that has been agreed on through Diffie-Hellman     * key agreement protocol.  Note that in the two party protocol, if     * the peer keys are already known, no other data needs to be sent in     * order to agree on a secret.  That is, a secured message may be     * sent without any mandatory round-trip overheads.     *     * <P>It is illegal to call this member function if the private key     * has not been set (or generated).     *     * @param peerPublicKey the peer's public key.     * @returns the secret, which is an unsigned big-endian integer     *  the same size as the Diffie-Hellman modulus.     */    SecretKey getAgreedSecret(BigInteger peerPublicValue) {        try {            KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman");            DHPublicKeySpec spec =                        new DHPublicKeySpec(peerPublicValue, modulus, base);            PublicKey publicKey = kf.generatePublic(spec);            KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman");            ka.init(privateKey);            ka.doPhase(publicKey, true);            return ka.generateSecret("TlsPremasterSecret");        } catch (GeneralSecurityException e) {            throw new RuntimeException("Could not generate secret", e);        }    } }