java.security
Class KeyFactory

java.lang.Object   
  java.security.KeyFactory

public class KeyFactory
extends Object   

Key factories are used to convert keys (opaque cryptographic keys of type Key) into key specifications (transparent representations of the underlying key material), and vice versa.

Key factories are bi-directional. That is, they allow you to build an opaque key object from a given key specification (key material), or to retrieve the underlying key material of a key object in a suitable format.

Multiple compatible key specifications may exist for the same key. For example, a DSA public key may be specified using DSAPublicKeySpec or X509EncodedKeySpec. A key factory can be used to translate between compatible key specifications.

The following is an example of how to use a key factory in order to instantiate a DSA public key from its encoding. Assume Alice has received a digital signature from Bob. Bob also sent her his public key (in encoded format) to verify his signature. Alice then performs the following actions:

 X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(bobEncodedPubKey);
 KeyFactory keyFactory = KeyFactory.getInstance("DSA");
 PublicKey bobPubKey = keyFactory.generatePublic(bobPubKeySpec);
 Signature sig = Signature.getInstance("DSA");
 sig.initVerify(bobPubKey);
 sig.update(data);
 sig.verify(signature);
 

Since:

1.2

See Also:

Key , PublicKey , PrivateKey , KeySpec , DSAPublicKeySpec , X509EncodedKeySpec

Constructor Summary

protected

KeyFactory (KeyFactorySpi keyFacSpi, Provider provider, String algorithm) Creates a KeyFactory object.

Method Summary

PrivateKey	generatePrivate (KeySpec keySpec) Generates a private key object from the provided key specification (key material).
PublicKey	generatePublic (KeySpec keySpec) Generates a public key object from the provided key specification (key material).
String	getAlgorithm () Gets the name of the algorithm associated with this KeyFactory.
static KeyFactory	getInstance (String algorithm) Generates a KeyFactory object that implements the specified algorithm.
static KeyFactory	getInstance (String algorithm, Provider provider) Generates a KeyFactory object for the specified algorithm from the specified provider.
static KeyFactory	getInstance (String algorithm, String provider) Generates a KeyFactory object for the specified algorithm from the specified provider.
<T extends KeySpec > T	getKeySpec (Key key, Class <T> keySpec) Returns a specification (key material) of the given key object.
Provider	getProvider () Returns the provider of this key factory object.
Key	translateKey (Key key) Translates a key object, whose provider may be unknown or potentially untrusted, into a corresponding key object of this key factory.

Methods inherited from class java.lang.Object

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

Constructor Detail

KeyFactory

protected KeyFactory(KeyFactorySpi    keyFacSpi,
                     Provider    provider,
                     String    algorithm)

Creates a KeyFactory object.

Parameters:

keyFacSpi - the delegate

provider - the provider

algorithm - the name of the algorithm to associate with this KeyFactory

Method Detail

getInstance

public static KeyFactory    getInstance(String    algorithm)
                              throws NoSuchAlgorithmException   

Generates a KeyFactory object that implements the specified algorithm. If the default provider package provides an implementation of the requested algorithm, an instance of KeyFactory containing that implementation is returned. If the algorithm is not available in the default package, other packages are searched.

Parameters:

algorithm - the name of the requested key algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Returns:

a KeyFactory object for the specified algorithm.

Throws:

NoSuchAlgorithmException - if the requested algorithm is not available in the default provider package or any of the other provider packages that were searched.

getInstance

public static KeyFactory    getInstance(String    algorithm,
                                     String    provider)
                              throws NoSuchAlgorithmException   ,
                                     NoSuchProviderException   

Generates a KeyFactory object for the specified algorithm from the specified provider.

Parameters:

algorithm - the name of the requested key algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

provider - the name of the provider.

Returns:

a KeyFactory object for the specified algorithm.

Throws:

NoSuchAlgorithmException - if the algorithm is not available from the specified provider.

NoSuchProviderException - if the provider has not been configured.

IllegalArgumentException - if the provider name is null or empty.

See Also:

Provider

getInstance

public static KeyFactory    getInstance(String    algorithm,
                                     Provider    provider)
                              throws NoSuchAlgorithmException   

Generates a KeyFactory object for the specified algorithm from the specified provider. Note: the provider doesn't have to be registered.

Parameters:

algorithm - the name of the requested key algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

provider - the provider.

Returns:

a KeyFactory object for the specified algorithm.

Throws:

NoSuchAlgorithmException - if the algorithm is not available from the specified provider.

IllegalArgumentException - if the provider is null.

Since:

1.4

See Also:

Provider

getProvider

public final Provider    getProvider()

Returns the provider of this key factory object.

Returns:

the provider of this key factory object

getAlgorithm

public final String    getAlgorithm()

Gets the name of the algorithm associated with this KeyFactory.

Returns:

the name of the algorithm associated with this KeyFactory

generatePublic

public final PublicKey    generatePublic(KeySpec    keySpec)
                               throws InvalidKeySpecException   

Generates a public key object from the provided key specification (key material).

Parameters:

keySpec - the specification (key material) of the public key.

Returns:

the public key.

Throws:

InvalidKeySpecException - if the given key specification is inappropriate for this key factory to produce a public key.

generatePrivate

public final PrivateKey    generatePrivate(KeySpec    keySpec)
                                 throws InvalidKeySpecException   

Generates a private key object from the provided key specification (key material).

Parameters:

keySpec - the specification (key material) of the private key.

Returns:

the private key.

Throws:

InvalidKeySpecException - if the given key specification is inappropriate for this key factory to produce a private key.

getKeySpec

public final <T extends KeySpec   > T getKeySpec(Key    key,
                                              Class   <T> keySpec)
                                   throws InvalidKeySpecException   

Returns a specification (key material) of the given key object. keySpec identifies the specification class in which the key material should be returned. It could, for example, be DSAPublicKeySpec.class, to indicate that the key material should be returned in an instance of the DSAPublicKeySpec class.

Parameters:

key - the key.

keySpec - the specification class in which the key material should be returned.

Returns:

the underlying key specification (key material) in an instance of the requested specification class.

Throws:

InvalidKeySpecException - if the requested key specification is inappropriate for the given key, or the given key cannot be processed (e.g., the given key has an unrecognized algorithm or format).

translateKey

public final Key    translateKey(Key    key)
                       throws InvalidKeyException   

Translates a key object, whose provider may be unknown or potentially untrusted, into a corresponding key object of this key factory.

Parameters:

key - the key whose provider is unknown or untrusted.

Returns:

the translated key.

Throws:

InvalidKeyException - if the given key cannot be processed by this key factory.