1 /* 2 * Copyright (c) 1996, 2012, 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 import java.io.IOException; 32 import javax.net.ssl.SSLHandshakeException; 33 import javax.crypto.SecretKey; 34 import javax.crypto.KeyAgreement; 35 import javax.crypto.interfaces.DHPublicKey; 36 import javax.crypto.spec.*; 37 38 import sun.security.util.KeyUtil; 39 40 /** 41 * This class implements the Diffie-Hellman key exchange algorithm. 42 * D-H means combining your private key with your partners public key to 43 * generate a number. The peer does the same with its private key and our 44 * public key. Through the magic of Diffie-Hellman we both come up with the 45 * same number. This number is secret (discounting MITM attacks) and hence 46 * called the shared secret. It has the same length as the modulus, e.g. 512 47 * or 1024 bit. Man-in-the-middle attacks are typically countered by an 48 * independent authentication step using certificates (RSA, DSA, etc.). 49 * 50 * The thing to note is that the shared secret is constant for two partners 51 * with constant private keys. This is often not what we want, which is why 52 * it is generally a good idea to create a new private key for each session. 53 * Generating a private key involves one modular exponentiation assuming 54 * suitable D-H parameters are available. 55 * 56 * General usage of this class (TLS DHE case): 57 * . if we are server, call DHCrypt(keyLength,random). This generates 58 * an ephemeral keypair of the request length. 59 * . if we are client, call DHCrypt(modulus, base, random). This 60 * generates an ephemeral keypair using the parameters specified by 61 * the server. 62 * . send parameters and public value to remote peer 63 * . receive peers ephemeral public key 64 * . call getAgreedSecret() to calculate the shared secret 65 * 66 * In TLS the server chooses the parameter values itself, the client must use 67 * those sent to it by the server. 68 * 69 * The use of ephemeral keys as described above also achieves what is called 70 * "forward secrecy". This means that even if the authentication keys are 71 * broken at a later date, the shared secret remains secure. The session is 72 * compromised only if the authentication keys are already broken at the 73 * time the key exchange takes place and an active MITM attack is used. 74 * This is in contrast to straightforward encrypting RSA key exchanges. 75 * 76 * @author David Brownell 77 */ 78 final class DHCrypt { 79 80 // group parameters (prime modulus and generator) 81 private BigInteger modulus; // P (aka N) 82 private BigInteger base; // G (aka alpha) 83 84 // our private key (including private component x) 85 private PrivateKey privateKey; 86 87 // public component of our key, X = (g ^ x) mod p 88 private BigInteger publicValue; // X (aka y) 89 90 // the times to recove from failure if public key validation 91 private static int MAX_FAILOVER_TIMES = 2; 92 93 /** 94 * Generate a Diffie-Hellman keypair of the specified size. 95 */ 96 DHCrypt(int keyLength, SecureRandom random) { 97 try { 98 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); 99 kpg.initialize(keyLength, random); 100 101 DHPublicKeySpec spec = generateDHPublicKeySpec(kpg); 102 if (spec == null) { 103 throw new RuntimeException("Could not generate DH keypair"); 104 } 105 106 publicValue = spec.getY(); 107 modulus = spec.getP(); 108 base = spec.getG(); 109 } catch (GeneralSecurityException e) { 110 throw new RuntimeException("Could not generate DH keypair", e); 111 } 112 } 113 114 115 /** 116 * Generate a Diffie-Hellman keypair using the specified parameters. 117 * 118 * @param modulus the Diffie-Hellman modulus P 119 * @param base the Diffie-Hellman base G 120 */ 121 DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) { 122 this.modulus = modulus; 123 this.base = base; 124 try { 125 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); 126 DHParameterSpec params = new DHParameterSpec(modulus, base); 127 kpg.initialize(params, random); 128 129 DHPublicKeySpec spec = generateDHPublicKeySpec(kpg); 130 if (spec == null) { 131 throw new RuntimeException("Could not generate DH keypair"); 132 } 133 134 publicValue = spec.getY(); 135 } catch (GeneralSecurityException e) { 136 throw new RuntimeException("Could not generate DH keypair", e); 137 } 138 } 139 140 141 static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) { 142 if (key instanceof DHPublicKey) { 143 DHPublicKey dhKey = (DHPublicKey)key; 144 DHParameterSpec params = dhKey.getParams(); 145 return new DHPublicKeySpec(dhKey.getY(), 146 params.getP(), params.getG()); 147 } 148 try { 149 KeyFactory factory = JsseJce.getKeyFactory("DH"); 150 return factory.getKeySpec(key, DHPublicKeySpec.class); 151 } catch (Exception e) { 152 throw new RuntimeException(e); 153 } 154 } 155 156 157 /** Returns the Diffie-Hellman modulus. */ 158 BigInteger getModulus() { 159 return modulus; 160 } 161 162 /** Returns the Diffie-Hellman base (generator). */ 163 BigInteger getBase() { 164 return base; 165 } 166 167 /** 168 * Gets the public key of this end of the key exchange. 169 */ 170 BigInteger getPublicKey() { 171 return publicValue; 172 } 173 174 /** 175 * Get the secret data that has been agreed on through Diffie-Hellman 176 * key agreement protocol. Note that in the two party protocol, if 177 * the peer keys are already known, no other data needs to be sent in 178 * order to agree on a secret. That is, a secured message may be 179 * sent without any mandatory round-trip overheads. 180 * 181 * <P>It is illegal to call this member function if the private key 182 * has not been set (or generated). 183 * 184 * @param peerPublicKey the peer's public key. 185 * @param keyIsValidated whether the {@code peerPublicKey} has beed 186 * validated 187 * @return the secret, which is an unsigned big-endian integer 188 * the same size as the Diffie-Hellman modulus. 189 */ 190 SecretKey getAgreedSecret(BigInteger peerPublicValue, 191 boolean keyIsValidated) throws IOException { 192 try { 193 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); 194 DHPublicKeySpec spec = 195 new DHPublicKeySpec(peerPublicValue, modulus, base); 196 PublicKey publicKey = kf.generatePublic(spec); 197 KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman"); 198 199 // validate the Diffie-Hellman public key 200 if (!keyIsValidated && 201 !KeyUtil.isOracleJCEProvider(ka.getProvider().getName())) { 202 try { 203 KeyUtil.validate(spec); 204 } catch (InvalidKeyException ike) { 205 // prefer handshake_failure alert to internal_error alert 206 throw new SSLHandshakeException(ike.getMessage()); 207 } 208 } 209 210 ka.init(privateKey); 211 ka.doPhase(publicKey, true); 212 return ka.generateSecret("TlsPremasterSecret"); 213 } catch (GeneralSecurityException e) { 214 throw new RuntimeException("Could not generate secret", e); 215 } 216 } 217 218 // Generate and validate DHPublicKeySpec 219 private DHPublicKeySpec generateDHPublicKeySpec(KeyPairGenerator kpg) 220 throws GeneralSecurityException { 221 222 boolean doExtraValiadtion = 223 (!KeyUtil.isOracleJCEProvider(kpg.getProvider().getName())); 224 for (int i = 0; i <= MAX_FAILOVER_TIMES; i++) { 225 KeyPair kp = kpg.generateKeyPair(); 226 privateKey = kp.getPrivate(); 227 DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); 228 229 // validate the Diffie-Hellman public key 230 if (doExtraValiadtion) { 231 try { 232 KeyUtil.validate(spec); 233 } catch (InvalidKeyException ivke) { 234 if (i == MAX_FAILOVER_TIMES) { 235 throw ivke; 236 } 237 // otherwise, ignore the exception and try the next one 238 continue; 239 } 240 } 241 242 return spec; 243 } 244 245 return null; 246 } 247 } 248
