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1 /* |
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2 * Copyright 1996-2007 Sun Microsystems, Inc. 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. Sun designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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22 * CA 95054 USA or visit www.sun.com if you need additional information or |
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23 * have any 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 |
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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 |
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37 /** |
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38 * This class implements the Diffie-Hellman key exchange algorithm. |
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39 * D-H means combining your private key with your partners public key to |
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40 * generate a number. The peer does the same with its private key and our |
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41 * public key. Through the magic of Diffie-Hellman we both come up with the |
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42 * same number. This number is secret (discounting MITM attacks) and hence |
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43 * called the shared secret. It has the same length as the modulus, e.g. 512 |
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44 * or 1024 bit. Man-in-the-middle attacks are typically countered by an |
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45 * independent authentication step using certificates (RSA, DSA, etc.). |
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46 * |
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47 * The thing to note is that the shared secret is constant for two partners |
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48 * with constant private keys. This is often not what we want, which is why |
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49 * it is generally a good idea to create a new private key for each session. |
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50 * Generating a private key involves one modular exponentiation assuming |
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51 * suitable D-H parameters are available. |
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52 * |
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53 * General usage of this class (TLS DHE case): |
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54 * . if we are server, call DHCrypt(keyLength,random). This generates |
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55 * an ephemeral keypair of the request length. |
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56 * . if we are client, call DHCrypt(modulus, base, random). This |
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57 * generates an ephemeral keypair using the parameters specified by the server. |
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58 * . send parameters and public value to remote peer |
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59 * . receive peers ephemeral public key |
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60 * . call getAgreedSecret() to calculate the shared secret |
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61 * |
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62 * In TLS the server chooses the parameter values itself, the client must use |
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63 * those sent to it by the server. |
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64 * |
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65 * The use of ephemeral keys as described above also achieves what is called |
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66 * "forward secrecy". This means that even if the authentication keys are |
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67 * broken at a later date, the shared secret remains secure. The session is |
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68 * compromised only if the authentication keys are already broken at the |
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69 * time the key exchange takes place and an active MITM attack is used. |
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70 * This is in contrast to straightforward encrypting RSA key exchanges. |
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71 * |
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72 * @author David Brownell |
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73 */ |
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74 final class DHCrypt { |
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75 |
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76 // group parameters (prime modulus and generator) |
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77 private BigInteger modulus; // P (aka N) |
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78 private BigInteger base; // G (aka alpha) |
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79 |
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80 // our private key (including private component x) |
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81 private PrivateKey privateKey; |
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82 |
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83 // public component of our key, X = (g ^ x) mod p |
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84 private BigInteger publicValue; // X (aka y) |
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85 |
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86 /** |
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87 * Generate a Diffie-Hellman keypair of the specified size. |
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88 */ |
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89 DHCrypt(int keyLength, SecureRandom random) { |
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90 try { |
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91 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); |
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92 kpg.initialize(keyLength, random); |
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93 KeyPair kp = kpg.generateKeyPair(); |
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94 privateKey = kp.getPrivate(); |
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95 DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); |
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96 publicValue = spec.getY(); |
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97 modulus = spec.getP(); |
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98 base = spec.getG(); |
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99 } catch (GeneralSecurityException e) { |
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100 throw new RuntimeException("Could not generate DH keypair", e); |
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101 } |
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102 } |
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103 |
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104 |
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105 /** |
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106 * Generate a Diffie-Hellman keypair using the specified parameters. |
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107 * |
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108 * @param modulus the Diffie-Hellman modulus P |
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109 * @param base the Diffie-Hellman base G |
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110 */ |
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111 DHCrypt(BigInteger modulus, BigInteger base, SecureRandom random) { |
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112 this.modulus = modulus; |
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113 this.base = base; |
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114 try { |
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115 KeyPairGenerator kpg = JsseJce.getKeyPairGenerator("DiffieHellman"); |
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116 DHParameterSpec params = new DHParameterSpec(modulus, base); |
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117 kpg.initialize(params, random); |
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118 KeyPair kp = kpg.generateKeyPair(); |
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119 privateKey = kp.getPrivate(); |
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120 DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic()); |
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121 publicValue = spec.getY(); |
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122 } catch (GeneralSecurityException e) { |
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123 throw new RuntimeException("Could not generate DH keypair", e); |
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124 } |
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125 } |
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126 |
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127 static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) { |
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128 if (key instanceof DHPublicKey) { |
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129 DHPublicKey dhKey = (DHPublicKey)key; |
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130 DHParameterSpec params = dhKey.getParams(); |
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131 return new DHPublicKeySpec(dhKey.getY(), params.getP(), params.getG()); |
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132 } |
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133 try { |
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134 KeyFactory factory = JsseJce.getKeyFactory("DH"); |
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135 return (DHPublicKeySpec)factory.getKeySpec |
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136 (key, DHPublicKeySpec.class); |
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137 } catch (Exception e) { |
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138 throw new RuntimeException(e); |
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139 } |
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140 } |
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141 |
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142 |
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143 /** Returns the Diffie-Hellman modulus. */ |
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144 BigInteger getModulus() { |
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145 return modulus; |
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146 } |
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147 |
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148 /** Returns the Diffie-Hellman base (generator). */ |
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149 BigInteger getBase() { |
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150 return base; |
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151 } |
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152 |
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153 /** |
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154 * Gets the public key of this end of the key exchange. |
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155 */ |
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156 BigInteger getPublicKey() { |
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157 return publicValue; |
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158 } |
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159 |
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160 /** |
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161 * Get the secret data that has been agreed on through Diffie-Hellman |
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162 * key agreement protocol. Note that in the two party protocol, if |
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163 * the peer keys are already known, no other data needs to be sent in |
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164 * order to agree on a secret. That is, a secured message may be |
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165 * sent without any mandatory round-trip overheads. |
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166 * |
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167 * <P>It is illegal to call this member function if the private key |
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168 * has not been set (or generated). |
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169 * |
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170 * @param peerPublicKey the peer's public key. |
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171 * @returns the secret, which is an unsigned big-endian integer |
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172 * the same size as the Diffie-Hellman modulus. |
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173 */ |
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174 SecretKey getAgreedSecret(BigInteger peerPublicValue) { |
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175 try { |
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176 KeyFactory kf = JsseJce.getKeyFactory("DiffieHellman"); |
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177 DHPublicKeySpec spec = |
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178 new DHPublicKeySpec(peerPublicValue, modulus, base); |
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179 PublicKey publicKey = kf.generatePublic(spec); |
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180 KeyAgreement ka = JsseJce.getKeyAgreement("DiffieHellman"); |
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181 ka.init(privateKey); |
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182 ka.doPhase(publicKey, true); |
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183 return ka.generateSecret("TlsPremasterSecret"); |
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184 } catch (GeneralSecurityException e) { |
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185 throw new RuntimeException("Could not generate secret", e); |
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186 } |
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187 } |
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188 |
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189 } |