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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 | } | ||