| /* |
| * Copyright 1996-2007 Sun Microsystems, Inc. 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. Sun designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| * CA 95054 USA or visit www.sun.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); |
| } |
| } |
| |
| } |