1 /*
2 * Copyright (c) 1996, 2017, 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 javax.net.ssl.SSLHandshakeException;
32 import javax.crypto.SecretKey;
33 import javax.crypto.KeyAgreement;
34 import javax.crypto.interfaces.DHPublicKey;
35 import javax.crypto.spec.*;
36 import java.util.EnumSet;
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 this(keyLength,
98 PredefinedDHParameterSpecs.definedParams.get(keyLength), random);
99 }
100
101 /**
102 * Generate a Diffie-Hellman keypair using the specified parameters.
103 *
104 * @param modulus the Diffie-Hellman modulus P
105 * @param base the Diffie-Hellman base G
106 */
107 DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) {
108 this(modulus.bitLength(),
109 new DHParameterSpec(modulus, base), random);
110 }
111
112 /**
113 * Generate a Diffie-Hellman keypair using the named group.
114 */
115 DHCrypt(NamedGroup namedGroup, SecureRandom random) {
116 this(-1, // The length (-1) is not used in the implementation.
117 SupportedGroupsExtension.getDHParameterSpec(namedGroup), random);
118 }
119
120 /**
121 * Generate a Diffie-Hellman keypair using the specified size and
122 * parameters.
123 */
124 private DHCrypt(int keyLength,
125 DHParameterSpec params, SecureRandom random) {
126
127 try {
128 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman");
129 if (params != null) {
130 kpg.initialize(params, random);
131 } else {
132 kpg.initialize(keyLength, random);
133 }
134
135 DHPublicKeySpec spec = generateDHPublicKeySpec(kpg);
136 if (spec == null) {
137 throw new RuntimeException("Could not generate DH keypair");
138 }
139
140 publicValue = spec.getY();
141 modulus = spec.getP();
142 base = spec.getG();
143 } catch (GeneralSecurityException e) {
144 throw new RuntimeException("Could not generate DH keypair", e);
145 }
146 }
147
148 static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) {
149 if (key instanceof DHPublicKey) {
150 DHPublicKey dhKey = (DHPublicKey)key;
151 DHParameterSpec params = dhKey.getParams();
152 return new DHPublicKeySpec(dhKey.getY(),
153 params.getP(), params.getG());
154 }
155 try {
156 KeyFactory factory = JsseJce.getKeyFactory("DiffieHellman");
157 return factory.getKeySpec(key, DHPublicKeySpec.class);
158 } catch (Exception e) {
159 throw new RuntimeException(e);
160 }
161 }
162
163
164 /** Returns the Diffie-Hellman modulus. */
165 BigInteger getModulus() {
166 return modulus;
167 }
168
169 /** Returns the Diffie-Hellman base (generator). */
170 BigInteger getBase() {
171 return base;
172 }
173
174 /**
175 * Gets the public key of this end of the key exchange.
176 */
177 BigInteger getPublicKey() {
178 return publicValue;
179 }
180
181 /**
182 * Get the secret data that has been agreed on through Diffie-Hellman
183 * key agreement protocol. Note that in the two party protocol, if
184 * the peer keys are already known, no other data needs to be sent in
185 * order to agree on a secret. That is, a secured message may be
186 * sent without any mandatory round-trip overheads.
187 *
188 * <P>It is illegal to call this member function if the private key
189 * has not been set (or generated).
190 *
191 * @param peerPublicKey the peer's public key.
192 * @param keyIsValidated whether the {@code peerPublicKey} has beed
193 * validated
194 * @return the secret, which is an unsigned big-endian integer
195 * the same size as the Diffie-Hellman modulus.
196 */
197 SecretKey getAgreedSecret(BigInteger peerPublicValue,
198 boolean keyIsValidated) throws SSLHandshakeException {
199 try {
200 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman");
201 DHPublicKeySpec spec =
202 new DHPublicKeySpec(peerPublicValue, modulus, base);
203 PublicKey publicKey = kf.generatePublic(spec);
204 KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman");
205
206 // validate the Diffie-Hellman public key
207 if (!keyIsValidated &&
208 !KeyUtil.isOracleJCEProvider(ka.getProvider().getName())) {
209 try {
210 KeyUtil.validate(spec);
211 } catch (InvalidKeyException ike) {
212 // prefer handshake_failure alert to internal_error alert
213 throw new SSLHandshakeException(ike.getMessage());
214 }
215 }
216
217 ka.init(privateKey);
218 ka.doPhase(publicKey, true);
219 return ka.generateSecret("TlsPremasterSecret");
220 } catch (GeneralSecurityException e) {
221 throw (SSLHandshakeException) new SSLHandshakeException(
222 "Could not generate secret").initCause(e);
223 }
224 }
225
226 // Check constraints of the specified DH public key.
227 void checkConstraints(AlgorithmConstraints constraints,
228 BigInteger peerPublicValue) throws SSLHandshakeException {
229
230 try {
231 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman");
232 DHPublicKeySpec spec =
233 new DHPublicKeySpec(peerPublicValue, modulus, base);
234 DHPublicKey publicKey = (DHPublicKey)kf.generatePublic(spec);
235
236 // check constraints of DHPublicKey
237 if (!constraints.permits(
238 EnumSet.of(CryptoPrimitive.KEY_AGREEMENT), publicKey)) {
239 throw new SSLHandshakeException(
240 "DHPublicKey does not comply to algorithm constraints");
241 }
242 } catch (GeneralSecurityException gse) {
243 throw (SSLHandshakeException) new SSLHandshakeException(
244 "Could not generate DHPublicKey").initCause(gse);
245 }
246 }
247
248 // Generate and validate DHPublicKeySpec
249 private DHPublicKeySpec generateDHPublicKeySpec(KeyPairGenerator kpg)
250 throws GeneralSecurityException {
251
252 boolean doExtraValiadtion =
253 (!KeyUtil.isOracleJCEProvider(kpg.getProvider().getName()));
254 for (int i = 0; i <= MAX_FAILOVER_TIMES; i++) {
255 KeyPair kp = kpg.generateKeyPair();
256 privateKey = kp.getPrivate();
257 DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic());
258
259 // validate the Diffie-Hellman public key
260 if (doExtraValiadtion) {
261 try {
262 KeyUtil.validate(spec);
263 } catch (InvalidKeyException ivke) {
264 if (i == MAX_FAILOVER_TIMES) {
265 throw ivke;
266 }
267 // otherwise, ignore the exception and try the next one
268 continue;
269 }
270 }
271
272 return spec;
273 }
274
275 return null;
276 }
277 }
278