1 /* |
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2 * Copyright (c) 1996, 2017, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 |
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27 package sun.security.ssl; |
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28 |
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29 import java.math.BigInteger; |
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30 import java.security.*; |
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31 import javax.net.ssl.SSLHandshakeException; |
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32 import javax.crypto.SecretKey; |
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33 import javax.crypto.KeyAgreement; |
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34 import javax.crypto.interfaces.DHPublicKey; |
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35 import javax.crypto.spec.*; |
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36 import java.util.EnumSet; |
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37 |
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38 import sun.security.util.KeyUtil; |
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39 |
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40 /** |
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41 * This class implements the Diffie-Hellman key exchange algorithm. |
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42 * D-H means combining your private key with your partners public key to |
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43 * generate a number. The peer does the same with its private key and our |
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44 * public key. Through the magic of Diffie-Hellman we both come up with the |
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45 * same number. This number is secret (discounting MITM attacks) and hence |
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46 * called the shared secret. It has the same length as the modulus, e.g. 512 |
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47 * or 1024 bit. Man-in-the-middle attacks are typically countered by an |
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48 * independent authentication step using certificates (RSA, DSA, etc.). |
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49 * |
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50 * The thing to note is that the shared secret is constant for two partners |
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51 * with constant private keys. This is often not what we want, which is why |
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52 * it is generally a good idea to create a new private key for each session. |
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53 * Generating a private key involves one modular exponentiation assuming |
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54 * suitable D-H parameters are available. |
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55 * |
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56 * General usage of this class (TLS DHE case): |
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57 * . if we are server, call DHCrypt(keyLength,random). This generates |
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58 * an ephemeral keypair of the request length. |
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59 * . if we are client, call DHCrypt(modulus, base, random). This |
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60 * generates an ephemeral keypair using the parameters specified by |
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61 * the server. |
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62 * . send parameters and public value to remote peer |
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63 * . receive peers ephemeral public key |
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64 * . call getAgreedSecret() to calculate the shared secret |
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65 * |
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66 * In TLS the server chooses the parameter values itself, the client must use |
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67 * those sent to it by the server. |
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68 * |
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69 * The use of ephemeral keys as described above also achieves what is called |
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70 * "forward secrecy". This means that even if the authentication keys are |
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71 * broken at a later date, the shared secret remains secure. The session is |
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72 * compromised only if the authentication keys are already broken at the |
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73 * time the key exchange takes place and an active MITM attack is used. |
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74 * This is in contrast to straightforward encrypting RSA key exchanges. |
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75 * |
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76 * @author David Brownell |
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77 */ |
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78 final class DHCrypt { |
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79 |
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80 // group parameters (prime modulus and generator) |
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81 private BigInteger modulus; // P (aka N) |
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82 private BigInteger base; // G (aka alpha) |
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83 |
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84 // our private key (including private component x) |
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85 private PrivateKey privateKey; |
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86 |
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87 // public component of our key, X = (g ^ x) mod p |
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88 private BigInteger publicValue; // X (aka y) |
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89 |
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90 // the times to recove from failure if public key validation |
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91 private static int MAX_FAILOVER_TIMES = 2; |
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92 |
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93 /** |
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94 * Generate a Diffie-Hellman keypair of the specified size. |
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95 */ |
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96 DHCrypt(int keyLength, SecureRandom random) { |
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97 this(keyLength, |
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98 PredefinedDHParameterSpecs.definedParams.get(keyLength), random); |
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99 } |
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100 |
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101 /** |
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102 * Generate a Diffie-Hellman keypair using the specified parameters. |
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103 * |
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104 * @param modulus the Diffie-Hellman modulus P |
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105 * @param base the Diffie-Hellman base G |
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106 */ |
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107 DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) { |
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108 this(modulus.bitLength(), |
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109 new DHParameterSpec(modulus, base), random); |
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110 } |
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111 |
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112 /** |
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113 * Generate a Diffie-Hellman keypair using the named group. |
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114 */ |
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115 DHCrypt(NamedGroup namedGroup, SecureRandom random) { |
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116 this(-1, // The length (-1) is not used in the implementation. |
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117 SupportedGroupsExtension.getDHParameterSpec(namedGroup), random); |
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118 } |
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119 |
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120 /** |
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121 * Generate a Diffie-Hellman keypair using the specified size and |
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122 * parameters. |
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123 */ |
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124 private DHCrypt(int keyLength, |
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125 DHParameterSpec params, SecureRandom random) { |
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126 |
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127 try { |
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128 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); |
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129 if (params != null) { |
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130 kpg.initialize(params, random); |
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131 } else { |
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132 kpg.initialize(keyLength, random); |
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133 } |
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134 |
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135 DHPublicKeySpec spec = generateDHPublicKeySpec(kpg); |
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136 if (spec == null) { |
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137 throw new RuntimeException("Could not generate DH keypair"); |
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138 } |
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139 |
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140 publicValue = spec.getY(); |
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141 modulus = spec.getP(); |
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142 base = spec.getG(); |
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143 } catch (GeneralSecurityException e) { |
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144 throw new RuntimeException("Could not generate DH keypair", e); |
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145 } |
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146 } |
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147 |
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148 static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) { |
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149 if (key instanceof DHPublicKey) { |
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150 DHPublicKey dhKey = (DHPublicKey)key; |
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151 DHParameterSpec params = dhKey.getParams(); |
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152 return new DHPublicKeySpec(dhKey.getY(), |
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153 params.getP(), params.getG()); |
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154 } |
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155 try { |
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156 KeyFactory factory = JsseJce.getKeyFactory("DiffieHellman"); |
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157 return factory.getKeySpec(key, DHPublicKeySpec.class); |
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158 } catch (Exception e) { |
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159 throw new RuntimeException(e); |
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160 } |
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161 } |
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162 |
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163 |
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164 /** Returns the Diffie-Hellman modulus. */ |
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165 BigInteger getModulus() { |
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166 return modulus; |
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167 } |
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168 |
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169 /** Returns the Diffie-Hellman base (generator). */ |
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170 BigInteger getBase() { |
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171 return base; |
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172 } |
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173 |
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174 /** |
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175 * Gets the public key of this end of the key exchange. |
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176 */ |
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177 BigInteger getPublicKey() { |
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178 return publicValue; |
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179 } |
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180 |
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181 /** |
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182 * Get the secret data that has been agreed on through Diffie-Hellman |
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183 * key agreement protocol. Note that in the two party protocol, if |
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184 * the peer keys are already known, no other data needs to be sent in |
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185 * order to agree on a secret. That is, a secured message may be |
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186 * sent without any mandatory round-trip overheads. |
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187 * |
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188 * <P>It is illegal to call this member function if the private key |
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189 * has not been set (or generated). |
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190 * |
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191 * @param peerPublicKey the peer's public key. |
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192 * @param keyIsValidated whether the {@code peerPublicKey} has beed |
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193 * validated |
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194 * @return the secret, which is an unsigned big-endian integer |
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195 * the same size as the Diffie-Hellman modulus. |
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196 */ |
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197 SecretKey getAgreedSecret(BigInteger peerPublicValue, |
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198 boolean keyIsValidated) throws SSLHandshakeException { |
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199 try { |
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200 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); |
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201 DHPublicKeySpec spec = |
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202 new DHPublicKeySpec(peerPublicValue, modulus, base); |
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203 PublicKey publicKey = kf.generatePublic(spec); |
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204 KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman"); |
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205 |
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206 // validate the Diffie-Hellman public key |
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207 if (!keyIsValidated && |
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208 !KeyUtil.isOracleJCEProvider(ka.getProvider().getName())) { |
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209 try { |
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210 KeyUtil.validate(spec); |
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211 } catch (InvalidKeyException ike) { |
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212 // prefer handshake_failure alert to internal_error alert |
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213 throw new SSLHandshakeException(ike.getMessage()); |
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214 } |
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215 } |
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216 |
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217 ka.init(privateKey); |
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218 ka.doPhase(publicKey, true); |
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219 return ka.generateSecret("TlsPremasterSecret"); |
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220 } catch (GeneralSecurityException e) { |
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221 throw (SSLHandshakeException) new SSLHandshakeException( |
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222 "Could not generate secret").initCause(e); |
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223 } |
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224 } |
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225 |
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226 // Check constraints of the specified DH public key. |
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227 void checkConstraints(AlgorithmConstraints constraints, |
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228 BigInteger peerPublicValue) throws SSLHandshakeException { |
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229 |
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230 try { |
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231 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); |
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232 DHPublicKeySpec spec = |
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233 new DHPublicKeySpec(peerPublicValue, modulus, base); |
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234 DHPublicKey publicKey = (DHPublicKey)kf.generatePublic(spec); |
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235 |
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236 // check constraints of DHPublicKey |
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237 if (!constraints.permits( |
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238 EnumSet.of(CryptoPrimitive.KEY_AGREEMENT), publicKey)) { |
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239 throw new SSLHandshakeException( |
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240 "DHPublicKey does not comply to algorithm constraints"); |
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241 } |
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242 } catch (GeneralSecurityException gse) { |
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243 throw (SSLHandshakeException) new SSLHandshakeException( |
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244 "Could not generate DHPublicKey").initCause(gse); |
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245 } |
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246 } |
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247 |
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248 // Generate and validate DHPublicKeySpec |
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249 private DHPublicKeySpec generateDHPublicKeySpec(KeyPairGenerator kpg) |
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250 throws GeneralSecurityException { |
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251 |
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252 boolean doExtraValiadtion = |
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253 (!KeyUtil.isOracleJCEProvider(kpg.getProvider().getName())); |
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254 for (int i = 0; i <= MAX_FAILOVER_TIMES; i++) { |
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255 KeyPair kp = kpg.generateKeyPair(); |
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256 privateKey = kp.getPrivate(); |
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257 DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); |
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258 |
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259 // validate the Diffie-Hellman public key |
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260 if (doExtraValiadtion) { |
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261 try { |
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262 KeyUtil.validate(spec); |
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263 } catch (InvalidKeyException ivke) { |
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264 if (i == MAX_FAILOVER_TIMES) { |
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265 throw ivke; |
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266 } |
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267 // otherwise, ignore the exception and try the next one |
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268 continue; |
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269 } |
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270 } |
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271 |
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272 return spec; |
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273 } |
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274 |
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275 return null; |
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276 } |
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277 } |
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278 |
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