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| 1 | +/* | |
| 2 | + * Copyright (c) 1996, 2008, Oracle and/or its affiliates. All rights reserved. | |
| 3 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 | + * | |
| 5 | + * This code is free software; you can redistribute it and/or modify it | |
| 6 | + * under the terms of the GNU General Public License version 2 only, as | |
| 7 | + * published by the Free Software Foundation. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 10 | + * | |
| 11 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 12 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 15 | + * accompanied this code). | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU General Public License version | |
| 18 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 19 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 20 | + * | |
| 21 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * questions. | |
| 24 | + */ | |
| 25 | + | |
| 26 | + | |
| 27 | +package sun.security.ssl; | |
| 28 | + | |
| 29 | +import java.math.BigInteger; | |
| 30 | +import java.security.*; | |
| 31 | + | |
| 32 | +import javax.crypto.SecretKey; | |
| 33 | +import javax.crypto.KeyAgreement; | |
| 34 | +import javax.crypto.interfaces.DHPublicKey; | |
| 35 | +import javax.crypto.spec.*; | |
| 36 | + | |
| 37 | +/** | |
| 38 | + * This class implements the Diffie-Hellman key exchange algorithm. | |
| 39 | + * D-H means combining your private key with your partners public key to | |
| 40 | + * generate a number. The peer does the same with its private key and our | |
| 41 | + * public key. Through the magic of Diffie-Hellman we both come up with the | |
| 42 | + * same number. This number is secret (discounting MITM attacks) and hence | |
| 43 | + * called the shared secret. It has the same length as the modulus, e.g. 512 | |
| 44 | + * or 1024 bit. Man-in-the-middle attacks are typically countered by an | |
| 45 | + * independent authentication step using certificates (RSA, DSA, etc.). | |
| 46 | + * | |
| 47 | + * The thing to note is that the shared secret is constant for two partners | |
| 48 | + * with constant private keys. This is often not what we want, which is why | |
| 49 | + * it is generally a good idea to create a new private key for each session. | |
| 50 | + * Generating a private key involves one modular exponentiation assuming | |
| 51 | + * suitable D-H parameters are available. | |
| 52 | + * | |
| 53 | + * General usage of this class (TLS DHE case): | |
| 54 | + * . if we are server, call DHCrypt(keyLength,random). This generates | |
| 55 | + * an ephemeral keypair of the request length. | |
| 56 | + * . if we are client, call DHCrypt(modulus, base, random). This | |
| 57 | + * generates an ephemeral keypair using the parameters specified by the server. | |
| 58 | + * . send parameters and public value to remote peer | |
| 59 | + * . receive peers ephemeral public key | |
| 60 | + * . call getAgreedSecret() to calculate the shared secret | |
| 61 | + * | |
| 62 | + * In TLS the server chooses the parameter values itself, the client must use | |
| 63 | + * those sent to it by the server. | |
| 64 | + * | |
| 65 | + * The use of ephemeral keys as described above also achieves what is called | |
| 66 | + * "forward secrecy". This means that even if the authentication keys are | |
| 67 | + * broken at a later date, the shared secret remains secure. The session is | |
| 68 | + * compromised only if the authentication keys are already broken at the | |
| 69 | + * time the key exchange takes place and an active MITM attack is used. | |
| 70 | + * This is in contrast to straightforward encrypting RSA key exchanges. | |
| 71 | + * | |
| 72 | + * @author David Brownell | |
| 73 | + */ | |
| 74 | +final class DHCrypt { | |
| 75 | + | |
| 76 | + // group parameters (prime modulus and generator) | |
| 77 | + private BigInteger modulus; // P (aka N) | |
| 78 | + private BigInteger base; // G (aka alpha) | |
| 79 | + | |
| 80 | + // our private key (including private component x) | |
| 81 | + private PrivateKey privateKey; | |
| 82 | + | |
| 83 | + // public component of our key, X = (g ^ x) mod p | |
| 84 | + private BigInteger publicValue; // X (aka y) | |
| 85 | + | |
| 86 | + /** | |
| 87 | + * Generate a Diffie-Hellman keypair of the specified size. | |
| 88 | + */ | |
| 89 | + DHCrypt(int keyLength, SecureRandom random) { | |
| 90 | + try { | |
| 91 | + KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); | |
| 92 | + kpg.initialize(keyLength, random); | |
| 93 | + KeyPair kp = kpg.generateKeyPair(); | |
| 94 | + privateKey = kp.getPrivate(); | |
| 95 | + DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); | |
| 96 | + publicValue = spec.getY(); | |
| 97 | + modulus = spec.getP(); | |
| 98 | + base = spec.getG(); | |
| 99 | + } catch (GeneralSecurityException e) { | |
| 100 | + throw new RuntimeException("Could not generate DH keypair", e); | |
| 101 | + } | |
| 102 | + } | |
| 103 | + | |
| 104 | + | |
| 105 | + /** | |
| 106 | + * Generate a Diffie-Hellman keypair using the specified parameters. | |
| 107 | + * | |
| 108 | + * @param modulus the Diffie-Hellman modulus P | |
| 109 | + * @param base the Diffie-Hellman base G | |
| 110 | + */ | |
| 111 | + DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) { | |
| 112 | + this.modulus = modulus; | |
| 113 | + this.base = base; | |
| 114 | + try { | |
| 115 | + KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); | |
| 116 | + DHParameterSpec params = new DHParameterSpec(modulus, base); | |
| 117 | + kpg.initialize(params, random); | |
| 118 | + KeyPair kp = kpg.generateKeyPair(); | |
| 119 | + privateKey = kp.getPrivate(); | |
| 120 | + DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); | |
| 121 | + publicValue = spec.getY(); | |
| 122 | + } catch (GeneralSecurityException e) { | |
| 123 | + throw new RuntimeException("Could not generate DH keypair", e); | |
| 124 | + } | |
| 125 | + } | |
| 126 | + | |
| 127 | + static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) { | |
| 128 | + if (key instanceof DHPublicKey) { | |
| 129 | + DHPublicKey dhKey = (DHPublicKey)key; | |
| 130 | + DHParameterSpec params = dhKey.getParams(); | |
| 131 | + return new DHPublicKeySpec(dhKey.getY(), params.getP(), params.getG()); | |
| 132 | + } | |
| 133 | + try { | |
| 134 | + KeyFactory factory = JsseJce.getKeyFactory("DH"); | |
| 135 | + return factory.getKeySpec(key, DHPublicKeySpec.class); | |
| 136 | + } catch (Exception e) { | |
| 137 | + throw new RuntimeException(e); | |
| 138 | + } | |
| 139 | + } | |
| 140 | + | |
| 141 | + | |
| 142 | + /** Returns the Diffie-Hellman modulus. */ | |
| 143 | + BigInteger getModulus() { | |
| 144 | + return modulus; | |
| 145 | + } | |
| 146 | + | |
| 147 | + /** Returns the Diffie-Hellman base (generator). */ | |
| 148 | + BigInteger getBase() { | |
| 149 | + return base; | |
| 150 | + } | |
| 151 | + | |
| 152 | + /** | |
| 153 | + * Gets the public key of this end of the key exchange. | |
| 154 | + */ | |
| 155 | + BigInteger getPublicKey() { | |
| 156 | + return publicValue; | |
| 157 | + } | |
| 158 | + | |
| 159 | + /** | |
| 160 | + * Get the secret data that has been agreed on through Diffie-Hellman | |
| 161 | + * key agreement protocol. Note that in the two party protocol, if | |
| 162 | + * the peer keys are already known, no other data needs to be sent in | |
| 163 | + * order to agree on a secret. That is, a secured message may be | |
| 164 | + * sent without any mandatory round-trip overheads. | |
| 165 | + * | |
| 166 | + * <P>It is illegal to call this member function if the private key | |
| 167 | + * has not been set (or generated). | |
| 168 | + * | |
| 169 | + * @param peerPublicKey the peer's public key. | |
| 170 | + * @returns the secret, which is an unsigned big-endian integer | |
| 171 | + * the same size as the Diffie-Hellman modulus. | |
| 172 | + */ | |
| 173 | + SecretKey getAgreedSecret(BigInteger peerPublicValue) { | |
| 174 | + try { | |
| 175 | + KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); | |
| 176 | + DHPublicKeySpec spec = | |
| 177 | + new DHPublicKeySpec(peerPublicValue, modulus, base); | |
| 178 | + PublicKey publicKey = kf.generatePublic(spec); | |
| 179 | + KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman"); | |
| 180 | + ka.init(privateKey); | |
| 181 | + ka.doPhase(publicKey, true); | |
| 182 | + return ka.generateSecret("TlsPremasterSecret"); | |
| 183 | + } catch (GeneralSecurityException e) { | |
| 184 | + throw new RuntimeException("Could not generate secret", e); | |
| 185 | + } | |
| 186 | + } | |
| 187 | + | |
| 188 | +} | |