iaik.security.dh

Class ESDHPrivateKey

java.lang.Object

iaik.pkcs.pkcs8.PrivateKeyInfo

iaik.security.dh.ESDHPrivateKey

All Implemented Interfaces:

ASN1Type, java.io.Serializable, java.security.Key, java.security.PrivateKey, javax.crypto.interfaces.DHKey, javax.crypto.interfaces.DHPrivateKey

public class ESDHPrivateKey
extends PrivateKeyInfo
implements javax.crypto.interfaces.DHPrivateKey, java.io.Serializable

This class implements a Diffie Hellman private key and supports ASN.1 encoding.

This class extends iaik.pkcs.pkcs8.PrivateKeyInfo for supporting the PKCS#8 Private Key Information Standard for ESDH private keys. ???????????????????????????????????????????????????????????????????????????????????? This class implements the javax.crypto.interfaces.DHPrivateKey interface for providing the functionality of a private key used for the DH key-exchange algorithm. ????????????????????????????????????????????????????????????????????????????????????

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 2(l-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 ESDHPrivateKey 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("ESDH");
 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("ESDH");
 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();
 

See Also:

PrivateKeyInfo, javax.crypto.interfaces.ESDHPrivateKey, KeyAgreement, javax.crypto.spec.ESDHGenParameterSpec, javax.crypto.spec.ESDHParameterSpec, javax.crypto.spec.ESDHPrivateKeySpec, javax.crypto.spec.ESDHPublicKeySpec, KeyPairGenerator, KeyPair, ESDHPublicKey, ESDHKeyPairGenerator, ESDHKeyFactory, ESDHParameters, ESDHParameterGenerator, ESDHKeyAgreement, Serialized Form

Field Summary

Fields inherited from class iaik.pkcs.pkcs8.PrivateKeyInfo

private_key_algorithm, private_key_info

Fields inherited from interface javax.crypto.interfaces.DHPrivateKey

serialVersionUID

Constructor Summary

Constructors

Constructor and Description
ESDHPrivateKey(ASN1Object obj) Creates a new ESDHPrivateKey from the given ASN.1 object.
ESDHPrivateKey(java.math.BigInteger x, ESDHParameterSpec parameters) Creates a new ESDHPrivateKey from given private key value x and ESDH parameter specification
ESDHPrivateKey(byte[] pk) Creates a new ESDHPrivateKey from the given DER encoded byte array.
ESDHPrivateKey(ESDHPrivateKeySpec keySpec) Creates a new ESDHPrivateKey from the given ESDHPrivateKeySpec representing the ESDH private key value x, and the values p, g, q, j (if available) and seed and pgenCounter (if available).
ESDHPrivateKey(java.io.InputStream is) Creates a new ESDHPrivateKey from an InputStream.

Method Summary

Methods

Modifier and Type	Method and Description
protected void	decode(byte[] privateKey) Decodes a DER encoded ESDH private key.
byte[]	encode() Returns this ESDH private key as DER encoded ASN.1 object.
java.lang.String	getAlgorithm() Returns the name of the appertaining algorithm.
javax.crypto.spec.DHParameterSpec	getParams() Returns the key parameters.
java.math.BigInteger	getX() Returns the private value x as BigInteger.
int	hashCode() Returns a hash code for this object.
java.lang.String	toString() Returns a string that represents the contents of this private key.

Methods inherited from class iaik.pkcs.pkcs8.PrivateKeyInfo

createPrivateKeyInfo, decode, equals, getEncoded, getFormat, getPrivateKey, getPrivateKey, toASN1Object, writeTo

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.security.Key

getEncoded, getFormat

Constructor Detail

ESDHPrivateKey

public ESDHPrivateKey(java.math.BigInteger x,
              ESDHParameterSpec parameters)

Creates a new ESDHPrivateKey from given private key value x and ESDH parameter specification

Parameters:

x - the BigInteger value representing the ESDH private key value

parameters - the ESDH parameters p (prime modulus), g (base generator), prime factor q, the subgroup factor j (if available) and the seed seed and pgenCounter pgenCounter (if available) as ESDHParameterSpec

See Also:

javax.crypto.spec.ESDHParameterSpec

ESDHPrivateKey

public ESDHPrivateKey(ESDHPrivateKeySpec keySpec)

Creates a new ESDHPrivateKey from the given ESDHPrivateKeySpec representing the ESDH private key value x, and the values p, g, q, j (if available) and seed and pgenCounter (if available).

Parameters:

keySpec - the ESDHPrivateKeySpec representing the private key value x, the prime modulus p, the base generator g, the subgroup factor j (if available) and the seed seed and pgenCounter pgenCounter (if available)

See Also:

DHPrivateKeySpec

ESDHPrivateKey

public ESDHPrivateKey(byte[] pk)
               throws java.security.InvalidKeyException

Creates a new ESDHPrivateKey from the given DER encoded byte array.

This constructor may be used for parsing an already exisiting ESDH private key, wrapped into a PKCS#8 PrivateKeyInfo that is supplied as DER encoded byte array.

Parameters:

the - byte array holding the DER encoded private key info

Throws:

java.security.InvalidKeyException - if something is wrong with the key encoding

ESDHPrivateKey

public ESDHPrivateKey(ASN1Object obj)
               throws java.security.InvalidKeyException

Creates a new ESDHPrivateKey from the given ASN.1 object. The supplied ASN1Object represents a PKCS#8 PrivateKeyInfo holding the ESDH private key.

Parameters:

obj - the private key ASN.1 data structure

Throws:

java.security.InvalidKeyException - if something is wrong with the key encoding

ESDHPrivateKey

public ESDHPrivateKey(java.io.InputStream is)
               throws java.io.IOException,
                      java.security.InvalidKeyException

Creates a new ESDHPrivateKey from an InputStream.

This constructor may be used for parsing an already exisiting ESDH private key, wrapped into a PKCS#8 PrivateKeyInfo that is supplied as DER encoded byte array.

Parameters:

is - the input stream with the data to be read to initialize the private key

Throws:

java.io.IOException - if an I/O error occurs

java.security.InvalidKeyException - if something is wrong with the key encoding

Method Detail

decode

protected void decode(byte[] privateKey)
               throws java.security.InvalidKeyException

Decodes a DER encoded ESDH private key.

From the given DER encoded byte array an ASN.1 object is created and parsed for the private key value x and the ESDH parameters prime p and base g, prime factor q, the subgroup factor j (if available) and the seed seed and pgenCounter pgenCounter (if available).

This method is protected and typically will not be used by an application. Rather it is used by the parent PKCS#8 PrivateKeyInfo class for decoding the inherent DH private key.

Specified by:

decode in class PrivateKeyInfo

Parameters:

privateKey - the DH private key as DER encoded ASN.1 object

Throws:

java.security.InvalidKeyException - if the given key is not a DH private key

encode

public byte[] encode()

Returns this ESDH private key as DER encoded ASN.1 object.

This method is protected and typically will not be used by an application. Rather it is used by the parent PKCS#8 PrivateKeyInfo class for encoding the inherent ESDH private key.

Specified by:

encode in class PrivateKeyInfo

Returns:

a byte array holding the ESDH private key as a DER encoded ASN.1 data structure

getX

public java.math.BigInteger getX()

Returns the private value x as BigInteger.

Specified by:

getX in interface javax.crypto.interfaces.DHPrivateKey

Returns:

the private value x as BigInteger

getParams

public javax.crypto.spec.DHParameterSpec getParams()

Returns the key parameters.

Specified by:

getParams in interface javax.crypto.interfaces.DHKey

Returns:

the key parameters as ESDHParameterSpec

getAlgorithm

public java.lang.String getAlgorithm()

Returns the name of the appertaining algorithm.

Specified by:

getAlgorithm in interface java.security.Key

Specified by:

getAlgorithm in class PrivateKeyInfo

Returns:

the string "ESDH"

hashCode

public int hashCode()

Returns a hash code for this object.

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code

toString

public java.lang.String toString()

Returns a string that represents the contents of this private key.

Overrides:

toString in class PrivateKeyInfo

Returns:

the string representation