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);

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.

Constructors

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

Methods

getInstance

public static KeyFactory getInstance(String algorithm)
                              throws NoSuchAlgorithmException

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:

NoSuchAlgorithmException - if no Provider supports a KeyFactorySpi implementation for the specified algorithm.

See Also:

Provider

getInstance

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

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.

provider - the name of the provider.

Returns:

the new KeyFactory object.

Throws:

NoSuchAlgorithmException - if a KeyFactorySpi implementation for the specified algorithm is not available from the specified provider.

NoSuchProviderException - if the specified provider is not registered in the security provider list.

IllegalArgumentException - if the provider name is null or empty.

See Also:

Provider

getInstance

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

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.

provider - the provider.

Returns:

the new KeyFactory object.

Throws:

NoSuchAlgorithmException - if a KeyFactorySpi implementation for the specified algorithm is not available from the specified Provider object.

IllegalArgumentException - if the specified 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.

Type Parameters:

T - the type of the key specification to be returned

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.