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);
 

Every implementation of the Java platform is required to support the following standard KeyFactory algorithms:

• DiffieHellman
• DSA
• RSA

These algorithms are described in the KeyFactory section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.

Since:

1.2

See Also:

Key, PublicKey, PrivateKey, KeySpec, DSAPublicKeySpec, X509EncodedKeySpec

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	KeyFactory(KeyFactorySpi keyFacSpi, Provider provider, String algorithm) Creates a KeyFactory object.

Method Summary

Methods

Modifier and Type	Method and Description
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) Returns a KeyFactory object that converts public/private keys of the specified algorithm.
static KeyFactory	getInstance(String algorithm, Provider provider) Returns a KeyFactory object that converts public/private keys of the specified algorithm.
static KeyFactory	getInstance(String algorithm, String provider) Returns a KeyFactory object that converts public/private keys of the specified algorithm.
<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

Returns a KeyFactory object that converts public/private keys of the specified algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyFactory object encapsulating the KeyFactorySpi implementation from the first Provider that supports the specified algorithm is returned.

Note that the list of registered providers may be retrieved via the Security.getProviders() method.

Parameters:

algorithm - the name of the requested key algorithm. See the KeyFactory section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Returns:

the new KeyFactory object.

Throws: