javax.crypto.interfaces
Interface DHPublicKey

All Superinterfaces:

DHKey, Key, PublicKey, Serializable

All Known Implementing Classes:

DHPublicKey, ESDHPublicKey

public interface DHPublicKey

extends DHKey, PublicKey

Interface to be implemented for supporting Diffie-Hellman public keys.

Attention: This is not a SUN implementation!

This class has been developed by IAIK according to the documentation publically available.
For SUN´s documentation of this class see http://java.sun.com/security/JCE1.2/spec/apidoc/index.html

The Diffie Hellman algorithm constitutes a key-exchange (or key-agreement) algorithm where some entities communicate according to a predescribed protocol for generating a shared secret only known by them.

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 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 be an entity itself), to perform two phases of the key agreement protocol:

• The first phase is performed independently by the two entities involved in the key agreement and uses the Diffie Hellman parameters derived from the central authority to randomly generate a private integer value x satisfying 0 < x < p-1. If the central authority has prescribed the length l of the private value x, it has to fulfill 2l-1 <= x < 2l. From the private value, the public value y is created by doing y = (gx)(mod p) with 0 < y < p. Subsequently each entity sends the public value just created to the other entity involved in the key agreement.

• The second phase again is performed independently by the two entities involved in the key agreement and uses the Diffie Hellman parameters derived from the central authority and the public value y' received from the other entity to finally create the shared secret z from the own private value x: z = (y'x)(mod p) with 0 < z < p.

There may be more than only two entities involved into a Diffie Hellman key agreement.

Any application wishing to be participated into a Diffie Hellman key agreement has to instantiate the javax.crypto.KeyAgreement class and initialize it with its DHPrivateKey for bringing in the required private information. A DH Hellman private key maybe generated using a proper key pair generator, e.g.:

 KeyPairGnerator dh_key_gen = KeyPairGenerator.getInstance("DH");
 dh_key_gen.initialize(1024);
 KeyPair dh_key_pair = dh_key_gen.generateKeyPair();
 DHPrivateKey dh_priv_key = (DHPrivateKey)dh_key_pair.getPrivate();
 KeyAgreement dh_key_agreement = KeyAgreement.getInstance("DH");
 dh_key_agreement.init(dh_priv_key);
 

Each phase of a key agreement is performed by a call to the doPhase method, supplied with some other entity´s public key or some intermediate key resulting from the last phase. When calling doPhase, it has to be specified whether to perform already the last phase of the key agreement or not by setting the lastPhase parameter to true or false:

 dh_key_agreement.doPhase(dhPubKey_from_other_entity, true);
 

Actually generating the shared secret is done by calling the generateSecret method:

 byte[] shared_secret = dh_key_agreemant.generateSecret();
 

Version:

File Revision 17

See Also:

DHKey, DHPrivateKey, KeyAgreement, KeyPairGenerator

Fields inherited from interface java.security.PublicKey

serialVersionUID

Method Summary

BigInteger

getY() Returns the public value y.

Methods inherited from interface javax.crypto.interfaces.DHKey

getParams

Methods inherited from interface java.security.Key

getAlgorithm, getEncoded, getFormat

Method Detail

getY

public BigInteger getY()

Returns the public value y.

Returns:

the public value y