iaik.security.dh
Class DHParameters

java.lang.Object
  |
  +--java.security.AlgorithmParametersSpi
        |
        +--iaik.security.dh.DHParameters

Direct Known Subclasses:

ESDHParameters

public class DHParameters

extends AlgorithmParametersSpi

This class represents Diffie Hellman paramters in opaque form and may be used for generating opaque DH parameters and converting them between various formats.

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.

DHParamters may be generated provider independently by calling one of the AlgorithmParameters.getInstance methods and subsequently initialzing the new AlgorithmParamters object with proper DH parameter specification or DER encoded byte array. If the first way is chosen, the parameter values (prime modulus p, base generator g and - if given - length l of the private value x) for initializing the new AlgorithmParameters object are immediately taken from the given DH parameter specification; if the parameters are given as DER encoded byte array, an ASN.1 object is created from this byte array for subsequently parsing it to get the Diffie Hellman parameters.

Alternatively DHParamerters may be created by using a proper AlgorithmParamterGenerator. The DHParameterGenerator itself calls AlgorithmParameters.getInstance("DH", "IAIK") for actually generating DHEParameters in opaque representation.

For obtaining DH parameters in transparent representation from an opaque DHParamters object, the getParameterSpec method can be used; for obtaining the parameters as DER encoded ASN.1 object, use getEncoded.

Version:

File Revision 15

See Also:

DHParameterGenerator, AlgorithmParameters, DHParameterSpec, DHPublicKey, DHPrivateKey, DHKeyPairGenerator, DHKeyFactory, DHKeyAgreement

Constructor Summary

DHParameters()
The default constructor.

Method Summary

protected byte[]	engineGetEncoded() Returns the parameters as DER byte array.
protected byte[]	engineGetEncoded(String format) Returns the parameters as DER byte array.
protected AlgorithmParameterSpec	engineGetParameterSpec(Class paramSpec) Returns the DH parameters as transparent DH parameter specification of the given class type.
protected void	engineInit(AlgorithmParameterSpec paramSpec) Initializes this DHParameters with prime modulus p, base generator g and length l of the private value x, derived from the given DHParameterSpec.
protected void	engineInit(byte[] params) Initializes this DHParameters object from the given DER encoded byte array.
protected void	engineInit(byte[] params, String format) Inits the parameters from a DER encoded byte array.
protected String	engineToString() Returns a String representation of the parameters.
int	hashCode() Returns a hash code for this object.

Methods inherited from class java.lang.Object

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

Constructor Detail

DHParameters

public DHParameters()

The default constructor. Only internally used for creating a DHParameters object. Applications shall use one of the AlgorithmParameter.getInstance factory methods for obtaining DHParameters.

Method Detail

engineGetEncoded

protected byte[] engineGetEncoded()
                           throws IOException

Returns the parameters as DER byte array.

A SEQUENCE ASN.1 object is created for holding prime modulus p, base generator g, and - if available - length l of the private value x; subsequently this SEQUENCE object is DER encoded to get the required byte array.

Overrides:

engineGetEncoded in class AlgorithmParametersSpi

Returns:

the DH parameters as DER byte array

Throws:

IOException - if an encoding error occurs

engineGetEncoded

protected byte[] engineGetEncoded(String format)
                           throws IOException

Returns the parameters as DER byte array.

Format is ignored. Only DER encoding is supported at this time. Only calls engineGetEncoded() for returning the DH paramters as DER encoded byte array, regardless of what is specified in the format string.

Overrides:

engineGetEncoded in class AlgorithmParametersSpi

Parameters:

format - the encoding format; ignored

Returns:

the DH parameters as DER byte array

Throws:

IOException - if an encoding error occurs

engineGetParameterSpec

protected AlgorithmParameterSpec engineGetParameterSpec(Class paramSpec)
                                                 throws InvalidParameterSpecException

Returns the DH parameters as transparent DH parameter specification of the given class type.

Overrides:

engineGetParameterSpec in class AlgorithmParametersSpi

Parameters:

paramSpec - the desired parameter specification class

Returns:

the DH parameters as AlgorithmParaneterSpec

Throws:

InvalidParameterSpecException - if the paramters cannot be converted to the desired parameter specification

engineInit

protected void engineInit(AlgorithmParameterSpec paramSpec)
                   throws InvalidParameterSpecException

Initializes this DHParameters with prime modulus p, base generator g and length l of the private value x, derived from the given DHParameterSpec.

Overrides:

engineInit in class AlgorithmParametersSpi

Parameters:

paramSpec - the parameter specification, which has to be a DHParameterSpec

Throws:

InvalidParameterSpecException - if the given parameter specification is not a DHParameterSpec

engineInit

protected void engineInit(byte[] params)
                   throws IOException

Initializes this DHParameters object from the given DER encoded byte array.

From the given byte array an ASN.1 object is created to be parsed for the required prime modulus p, base generator g and - if included - length l of the private value x.

Overrides:

engineInit in class AlgorithmParametersSpi

Parameters:

params - the DER encoded byte array

Throws:

IOException - if an error occurs when decoding the given byte array

engineInit

protected void engineInit(byte[] params,
                          String format)
                   throws IOException

Inits the parameters from a DER encoded byte array. Format is ignored.

Only calls engineInit(params) for initializing this DHParamters object from the given DER encoded byte array, regardless of what is specified in the format string.

Overrides:

engineInit in class AlgorithmParametersSpi

Parameters:

params - the DER encoded byte array

format - the encoding format; ignored

Throws:

IOException - if an error occurs when decoding the given byte array

hashCode

public int hashCode()

Returns a hash code for this object.

Overrides:

hashCode in class Object

Returns:

the hash code

engineToString

protected String engineToString()

Returns a String representation of the parameters.

Overrides:

engineToString in class AlgorithmParametersSpi

Returns:

a String representation of this DHParameters object