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);
 

Android provides the following KeyFactory algorithms:

Name Supported (API Levels)
DH 1+
DSA 1+
EC 11+
RSA 1+
X.509 1–8
These algorithms are described in the KeyFactory section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

Protected Constructor Summary

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

Public Method Summary

final PrivateKey
generatePrivate(KeySpec keySpec)
Generates a private key object from the provided key specification (key material).
final PublicKey
generatePublic(KeySpec keySpec)
Generates a public key object from the provided key specification (key material).
final 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, String provider)
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.
final <T extends KeySpec> T
getKeySpec(Key key, Class<T> keySpec)
Returns a specification (key material) of the given key object.
final Provider
getProvider()
Returns the provider of this key factory object.
final 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.

Inherited Method Summary

Protected Constructors

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

Public Methods

public final PrivateKey generatePrivate (KeySpec keySpec)

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.

public final PublicKey generatePublic (KeySpec keySpec)

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.

public final String getAlgorithm ()

Gets the name of the algorithm associated with this KeyFactory.

Returns
  • the name of the algorithm associated with this KeyFactory

public static KeyFactory getInstance (String algorithm)

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

public static KeyFactory getInstance (String algorithm, String provider)

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

A new KeyFactory object encapsulating the KeyFactorySpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

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.
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

public static KeyFactory getInstance (String algorithm, Provider provider)

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

A new KeyFactory object encapsulating the KeyFactorySpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.

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.
See Also

public final T getKeySpec (Key key, Class<T> keySpec)

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).

public final Provider getProvider ()

Returns the provider of this key factory object.

Returns
  • the provider of this key factory object

public final 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.

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.