DHPrivateKey ("Entrust Authority Security Toolkit for the Java Platform")

java.lang.Object
- iaik.pkcs.pkcs8.PrivateKeyInfo
- - iaik.security.dh.DHPrivateKey

All Implemented Interfaces:

ASN1Type, java.io.Serializable, java.security.Key, java.security.PrivateKey, javax.crypto.interfaces.DHKey, javax.crypto.interfaces.DHPrivateKey
```
public class DHPrivateKey
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 DH 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 < 2^l. From the private value, the public value y is created by doing y = (g^x)(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();
 
```
See Also:
PrivateKeyInfo, DHPrivateKey, KeyAgreement, DHGenParameterSpec, DHParameterSpec, DHPrivateKeySpec, DHPublicKeySpec, KeyPairGenerator, KeyPair, DHPublicKey, DHKeyPairGenerator, DHKeyFactory, DHParameters, DHParameterGenerator, DHKeyAgreement, 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
`DHPrivateKey(ASN1Object obj)` Creates a new DHPrivateKey from the given ASN.1 object.
`DHPrivateKey(java.math.BigInteger x, javax.crypto.spec.DHParameterSpec parameters)` Creates a new DHPrivateKey from given private key value x and DH parameter specification
`DHPrivateKey(byte[] pk)` Creates a new DHPrivateKey from the given DER encoded byte array.
`DHPrivateKey(javax.crypto.spec.DHPrivateKeySpec keySpec)` Creates a new DHPrivateKey from the given DHPrivateKeySpec representing the DH private key value x, and the public values p, g and l.
`DHPrivateKey(java.io.InputStream is)` Creates a new DHPrivateKey from an InputStream.

Method Summary

Methods
Modifier and Type	Method and Description
`protected void`	`decode(byte[] privateKey)` Decodes a DER encoded DH private key.
`byte[]`	`encode()` Returns this DH 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
  - DHPrivateKey
```
public DHPrivateKey(java.math.BigInteger x,
            javax.crypto.spec.DHParameterSpec parameters)
```
    Creates a new DHPrivateKey from given private key value x and DH parameter specification
    
    Parameters:
    x - the BigInteger value representing the DH private key value
    parameters - the DH parameters p (prime modulus), g (base generator) and l (length of the private value x) as DHParameterSpec
    See Also:
    DHParameterSpec
  - DHPrivateKey
```
public DHPrivateKey(javax.crypto.spec.DHPrivateKeySpec keySpec)
```
    Creates a new DHPrivateKey from the given DHPrivateKeySpec representing the DH private key value x, and the public values p, g and l.
    
    Parameters:
    keySpec - the DHPrivateKeySpec representing the private key value x, the prime modulus p, the base generator g, and the length l of the private value
    See Also:
    DHPrivateKeySpec
  - DHPrivateKey
```
public DHPrivateKey(byte[] pk)
             throws java.security.InvalidKeyException
```
    Creates a new DHPrivateKey from the given DER encoded byte array.
    This constructor may be used for parsing an already exisiting DH 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
  - DHPrivateKey
```
public DHPrivateKey(ASN1Object obj)
             throws java.security.InvalidKeyException
```
    Creates a new DHPrivateKey from the given ASN.1 object. The supplied ASN1Object represents a PKCS#8 PrivateKeyInfo holding the DH private key.
    
    Parameters:
    obj - the private key ASN.1 data structure
    
    Throws:
    
    java.security.InvalidKeyException - if something is wrong with the key encoding
  - DHPrivateKey
```
public DHPrivateKey(java.io.InputStream is)
             throws java.io.IOException,
                    java.security.InvalidKeyException
```
    Creates a new DHPrivateKey from an InputStream.
    This constructor may be used for parsing an already exisiting DH 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 DH 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 DH parameters prime p and base g, and - if included - the length l of the private value x.
    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 DH 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 DH private key.
    
    Specified by:
    
    encode in class PrivateKeyInfo
    
    Returns:
    a byte array holding the DH 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 DHParameterSpec
  - 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 "DH"
  - 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

Class DHPrivateKey

Field Summary

Fields inherited from class iaik.pkcs.pkcs8.PrivateKeyInfo

Fields inherited from interface javax.crypto.interfaces.DHPrivateKey

Constructor Summary

Method Summary

Methods inherited from class iaik.pkcs.pkcs8.PrivateKeyInfo

Methods inherited from class java.lang.Object

Methods inherited from interface java.security.Key

Constructor Detail

DHPrivateKey

DHPrivateKey

DHPrivateKey

DHPrivateKey

DHPrivateKey

Method Detail

decode

encode

getX

getParams

getAlgorithm

hashCode

toString