J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1996-2007 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any 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 (DHPublicKeySpec)factory.getKeySpec |
| 136 | (key, DHPublicKeySpec.class); |
| 137 | } catch (Exception e) { |
| 138 | throw new RuntimeException(e); |
| 139 | } |
| 140 | } |
| 141 | |
| 142 | |
| 143 | /** Returns the Diffie-Hellman modulus. */ |
| 144 | BigInteger getModulus() { |
| 145 | return modulus; |
| 146 | } |
| 147 | |
| 148 | /** Returns the Diffie-Hellman base (generator). */ |
| 149 | BigInteger getBase() { |
| 150 | return base; |
| 151 | } |
| 152 | |
| 153 | /** |
| 154 | * Gets the public key of this end of the key exchange. |
| 155 | */ |
| 156 | BigInteger getPublicKey() { |
| 157 | return publicValue; |
| 158 | } |
| 159 | |
| 160 | /** |
| 161 | * Get the secret data that has been agreed on through Diffie-Hellman |
| 162 | * key agreement protocol. Note that in the two party protocol, if |
| 163 | * the peer keys are already known, no other data needs to be sent in |
| 164 | * order to agree on a secret. That is, a secured message may be |
| 165 | * sent without any mandatory round-trip overheads. |
| 166 | * |
| 167 | * <P>It is illegal to call this member function if the private key |
| 168 | * has not been set (or generated). |
| 169 | * |
| 170 | * @param peerPublicKey the peer's public key. |
| 171 | * @returns the secret, which is an unsigned big-endian integer |
| 172 | * the same size as the Diffie-Hellman modulus. |
| 173 | */ |
| 174 | SecretKey getAgreedSecret(BigInteger peerPublicValue) { |
| 175 | try { |
| 176 | KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); |
| 177 | DHPublicKeySpec spec = |
| 178 | new DHPublicKeySpec(peerPublicValue, modulus, base); |
| 179 | PublicKey publicKey = kf.generatePublic(spec); |
| 180 | KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman"); |
| 181 | ka.init(privateKey); |
| 182 | ka.doPhase(publicKey, true); |
| 183 | return ka.generateSecret("TlsPremasterSecret"); |
| 184 | } catch (GeneralSecurityException e) { |
| 185 | throw new RuntimeException("Could not generate secret", e); |
| 186 | } |
| 187 | } |
| 188 | |
| 189 | } |