iaik.security.dh

Class DHParameterGenerator

java.lang.Object

java.security.AlgorithmParameterGeneratorSpi

iaik.security.dh.DHParameterGenerator

Direct Known Subclasses:

ESDHParameterGenerator

public class DHParameterGenerator
extends java.security.AlgorithmParameterGeneratorSpi

This class implements an AlgorithmParameterGenerator that generates parameters for key-agreement according to the Diffie-Hellman protocol.

The algorithm used is taken from RFC 2631. It specifies a minimum prime length of 512 bit and minimum exponent length of 160 bit; defaults in this implementation are 1024 and 300 bits respectively. Access to the verification parameters provided by the generation algorithm is not possible with the current API.

Note that parameter generation is fairly slow but this should not be a problem as this is a hardly performed activity anyway. Typically they will be generated once per user group by the CA and then the users will generate their keys using the parameters provided.

The Diffie Hellman algorithm has been the first public-key algorithm. It only can be used for key-agreement, but not for data encrypting and decrypting.

PKCS#3 describes a method for implementing the Diffie Hellman key agreement where two (or more) entities use general Diffie Hellman parameters (an odd prime p, an integer base g satisfying 0 < g < p, and optionally an integer l prescribing the length of the private value), generated from some central authority (which may an entity itself), for creating a shared secret only known by them.

Applications shall use AlgorithmParameterGenerator.getInstance("DH") for obtaining an AlgorithmParamterGenerator for generating DH parameters in opaque representation. Once the generator has been created, it shall be properly initialized by one of the several init methods. If none explicit initialization is done, per default the length of the prime modulus is set to 512 bits and the length of the exponent (private value) is chosen to be 8 bits shorter, i.e. 504 bits. After initializing the generator (or relying on default settings), the reguired parameters actually are created by calling the generateParameters method.

See Also:

AlgorithmParameterGenerator, DHParameterSpec, DHParameters, DHPublicKey, DHPrivateKey, DHKeyPairGenerator, DHKeyFactory, DHKeyAgreement

Constructor Summary

Constructors

Constructor and Description
DHParameterGenerator() The default constructor.

Method Summary

Modifier and Type	Method and Description
protected java.security.AlgorithmParameters	engineGenerateParameters() Actually generates the required DH AlgorithmParameters.
protected void	engineInit(java.security.spec.AlgorithmParameterSpec param, java.security.SecureRandom random) Initializes this generator with DH-specific parameter generation values and some random seed.
protected void	engineInit(int primeLength, java.security.SecureRandom random) Initializes the parameter generator with given prime modulus length and random seed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DHParameterGenerator

public DHParameterGenerator()

The default constructor. Only internally used for creating an DHParameterGenerator object. Applications shall use one of the AlgorithmParameterGenerator.getInstance factory methods for obtaining an AlgorithmParamterGenerator for generating paramters for Diffie Hellman key agreement.

Method Detail

engineInit

protected void engineInit(int primeLength,
                          java.security.SecureRandom random)

Initializes the parameter generator with given prime modulus length and random seed. Exponent length is set to 0.

Specified by:

engineInit in class java.security.AlgorithmParameterGeneratorSpi

Parameters:

primeLength - the length of the prime modulus in bits

random - the random seed for this generator.

engineInit

protected void engineInit(java.security.spec.AlgorithmParameterSpec param,
                          java.security.SecureRandom random)
                   throws java.security.InvalidAlgorithmParameterException

Initializes this generator with DH-specific parameter generation values and some random seed.

From the given parameter specification DHGenParameterSpec) prime modulus length and exponent length are obtained for generating the algorithm parameters.

Applications shall call init(param_spec, random) for provider independently accessing this method.

Specified by:

engineInit in class java.security.AlgorithmParameterGeneratorSpi

Parameters:

param - an instance of DHGenParameterSpec

random - the random seed to be used by this generator.

Throws:

java.security.InvalidAlgorithmParameterException - if param is not an instance of DHGenParameterSpec or if the size of the exponent is not shorter than that of the prime modulus

engineGenerateParameters

protected java.security.AlgorithmParameters engineGenerateParameters()

Actually generates the required DH AlgorithmParameters.

Applications shall call generatePrameters() for provider independently accessing this method.

Specified by:

engineGenerateParameters in class java.security.AlgorithmParameterGeneratorSpi

Returns:

the new created Diffie Hellman AlgorithmParameters