java.security

Class 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

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, String provider)
Generates a KeyFactory object for the specified algorithm from the specified provider.
static KeyFactory
getInstance(String algorithm, Provider provider)
Generates a KeyFactory object for the specified algorithm from the specified provider.
KeySpec
getKeySpec(Key key, Class 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 Details

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 Details

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.

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.

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.

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

getKeySpec

public final KeySpec getKeySpec(Key key,
                                Class 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).

getProvider

public final Provider getProvider()
Returns the provider of this key factory object.
Returns:
the provider of this key factory object.

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.

KeyFactory.java --- Key Factory Class Copyright (C) 1999, 2003, 2004 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.