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    1   /*
    2    * Copyright (c) 1997, 2007, 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   package com.sun.crypto.provider;
   27   
   28   import java.math.BigInteger;
   29   import java.security;
   30   import java.security.spec;
   31   import javax.crypto.spec.DHParameterSpec;
   32   import javax.crypto.spec.DHGenParameterSpec;
   33   
   34   /*
   35    * This class generates parameters for the Diffie-Hellman algorithm.
   36    * The parameters are a prime, a base, and optionally the length in bits of
   37    * the private value.
   38    *
   39    * <p>The Diffie-Hellman parameter generation accepts the size in bits of the
   40    * prime modulus and the size in bits of the random exponent as input.
   41    * The size of the prime modulus defaults to 1024 bits.
   42    *
   43    * @author Jan Luehe
   44    *
   45    *
   46    * @see java.security.AlgorithmParameters
   47    * @see java.security.spec.AlgorithmParameterSpec
   48    * @see DHParameters
   49    */
   50   public final class DHParameterGenerator
   51   extends AlgorithmParameterGeneratorSpi {
   52   
   53       // The size in bits of the prime modulus
   54       private int primeSize = 1024;
   55   
   56       // The size in bits of the random exponent (private value)
   57       private int exponentSize = 0;
   58   
   59       // The source of randomness
   60       private SecureRandom random = null;
   61   
   62       /**
   63        * Initializes this parameter generator for a certain keysize
   64        * and source of randomness.
   65        * The keysize is specified as the size in bits of the prime modulus.
   66        *
   67        * @param keysize the keysize (size of prime modulus) in bits
   68        * @param random the source of randomness
   69        */
   70       protected void engineInit(int keysize, SecureRandom random) {
   71           if ((keysize < 512) || (keysize > 1024) || (keysize % 64 != 0)) {
   72               throw new InvalidParameterException("Keysize must be multiple "
   73                                                   + "of 64, and can only range "
   74                                                   + "from 512 to 1024 "
   75                                                   + "(inclusive)");
   76           }
   77           this.primeSize = keysize;
   78           this.random = random;
   79       }
   80   
   81       /**
   82        * Initializes this parameter generator with a set of parameter
   83        * generation values, which specify the size of the prime modulus and
   84        * the size of the random exponent, both in bits.
   85        *
   86        * @param params the set of parameter generation values
   87        * @param random the source of randomness
   88        *
   89        * @exception InvalidAlgorithmParameterException if the given parameter
   90        * generation values are inappropriate for this parameter generator
   91        */
   92       protected void engineInit(AlgorithmParameterSpec genParamSpec,
   93                                 SecureRandom random)
   94           throws InvalidAlgorithmParameterException {
   95               if (!(genParamSpec instanceof DHGenParameterSpec)) {
   96                   throw new InvalidAlgorithmParameterException
   97                       ("Inappropriate parameter type");
   98               }
   99   
  100               DHGenParameterSpec dhParamSpec = (DHGenParameterSpec)genParamSpec;
  101   
  102               primeSize = dhParamSpec.getPrimeSize();
  103               if ((primeSize<512) || (primeSize>1024) || (primeSize%64 != 0)) {
  104                   throw new InvalidAlgorithmParameterException
  105                       ("Modulus size must be multiple of 64, and can only range "
  106                        + "from 512 to 1024 (inclusive)");
  107               }
  108   
  109               exponentSize = dhParamSpec.getExponentSize();
  110               if (exponentSize <= 0) {
  111                   throw new InvalidAlgorithmParameterException
  112                       ("Exponent size must be greater than zero");
  113               }
  114   
  115               // Require exponentSize < primeSize
  116               if (exponentSize >= primeSize) {
  117                   throw new InvalidAlgorithmParameterException
  118                       ("Exponent size must be less than modulus size");
  119               }
  120       }
  121   
  122       /**
  123        * Generates the parameters.
  124        *
  125        * @return the new AlgorithmParameters object
  126        */
  127       protected AlgorithmParameters engineGenerateParameters() {
  128           AlgorithmParameters algParams = null;
  129   
  130           if (this.exponentSize == 0) {
  131               this.exponentSize = this.primeSize - 1;
  132           }
  133   
  134           if (this.random == null)
  135               this.random = SunJCE.RANDOM;
  136   
  137           try {
  138               AlgorithmParameterGenerator paramGen;
  139               DSAParameterSpec dsaParamSpec;
  140   
  141               paramGen = AlgorithmParameterGenerator.getInstance("DSA");
  142               paramGen.init(this.primeSize, random);
  143               algParams = paramGen.generateParameters();
  144               dsaParamSpec = (DSAParameterSpec)
  145                   algParams.getParameterSpec(DSAParameterSpec.class);
  146   
  147               DHParameterSpec dhParamSpec;
  148               if (this.exponentSize > 0) {
  149                   dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),
  150                                                     dsaParamSpec.getG(),
  151                                                     this.exponentSize);
  152               } else {
  153                   dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),
  154                                                     dsaParamSpec.getG());
  155               }
  156               algParams = AlgorithmParameters.getInstance("DH", "SunJCE");
  157               algParams.init(dhParamSpec);
  158           } catch (InvalidParameterSpecException e) {
  159               // this should never happen
  160               throw new RuntimeException(e.getMessage());
  161           } catch (NoSuchAlgorithmException e) {
  162               // this should never happen, because we provide it
  163               throw new RuntimeException(e.getMessage());
  164           } catch (NoSuchProviderException e) {
  165               // this should never happen, because we provide it
  166               throw new RuntimeException(e.getMessage());
  167           }
  168   
  169           return algParams;
  170       }
  171   }

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