javax.crypto
Class KeyGenerator

java.lang.Object
  javax.crypto.KeyGenerator

public class KeyGenerator
extends Object

This class provides the functionality of a (symmetric) key generator.

Key generators are constructed using one of the getInstance class methods of this class.

KeyGenerator objects are reusable, i.e., after a key has been generated, the same KeyGenerator object can be re-used to generate further keys.

There are two ways to generate a key: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object:

• Algorithm-Independent Initialization

  All key generators share the concepts of a keysize and a source of randomness. There is an init method in this KeyGenerator class that takes these two universally shared types of arguments. There is also one that takes just a keysize argument, and uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation), and one that takes just a source of randomness.

  Since no other parameters are specified when you call the above algorithm-independent init methods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.

• Algorithm-Specific Initialization

  For situations where a set of algorithm-specific parameters already exists, there are two init methods that have an AlgorithmParameterSpec argument. One also has a SecureRandom argument, while the other uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation).

In case the client does not explicitly initialize the KeyGenerator (via a call to an init method), each provider must supply (and document) a default initialization.

Version:

"$Id: KeyGenerator.java 1913 2007-08-08 02:41:53Z jpeters $"

Author:

Patric Kabus, Jan Peters

Field Summary

private String	algorithm_ The algorithm used by this instance.
private KeyGeneratorSpi	keyGenSpi_ The key generator used by this instance.
private Provider	provider_ The provider used by this instance.

Constructor Summary

protected

KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm) Creates a new KeyGenerator object.

Method Summary

SecretKey	generateKey() Generates a secret key.
String	getAlgorithm() Returns the algorithm name of this KeyGenerator object.
static KeyGenerator	getInstance(String algorithm) Generates a KeyGenerator object for the specified agorithm.
static KeyGenerator	getInstance(String algorithm, Provider provider) Generates a KeyGenerator object for the specified key algorithm from the specified provider.
static KeyGenerator	getInstance(String algorithm, String provider) Generates a KeyGenerator object for the specified key algorithm from the specified provider.
Provider	getProvider() Returns the provider of this KeyGenerator object.
void	init(AlgorithmParameterSpec params) Initializes this key generator with the specified parameter set.
void	init(AlgorithmParameterSpec params, SecureRandom random) Initializes the key generator with the specified parameter set and a user-provided source of randomness.
void	init(int keysize) Initializes this key generator for a certain keysize.
void	init(int keysize, SecureRandom random) Initializes this key generator for a certain keysize, using the given source of randomness.
void	init(SecureRandom random) Initializes the key generator.

Methods inherited from class java.lang.Object

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

Field Detail

keyGenSpi_

private KeyGeneratorSpi keyGenSpi_

The key generator used by this instance.

provider_

private Provider provider_

The provider used by this instance.

algorithm_

private String algorithm_

The algorithm used by this instance.

Constructor Detail

KeyGenerator

protected KeyGenerator(KeyGeneratorSpi keyGenSpi,
                       Provider provider,
                       String algorithm)

Creates a new KeyGenerator object.

Parameters:

keyGenSpi - the delegate.

provider - the provider.

algorithm - the algorithm.

Method Detail

getAlgorithm

public final String getAlgorithm()

Returns the algorithm name of this KeyGenerator object.

This is the same name that was specified in one of the getInstance calls that created this KeyGenerator object.

Returns:

the algorithm name of this KeyGenerator object.

getInstance

public static final KeyGenerator getInstance(String algorithm)
                                      throws NoSuchAlgorithmException

Generates a KeyGenerator object for the specified agorithm. If the default provider package provides an implementation of the requested key generator, an instance of KeyGenerator containing that implementation is returned. If the requested key generator is not available in the default provider package, other provider packages are searched.

Parameters:

algorithm - the standard name of the requested key algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

Returns:

the new KeyGenerator object.

Throws:

NullPointerException - if the specified algorithm is null.

NoSuchAlgorithmException - if a key generator for the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

getInstance

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

Generates a KeyGenerator object for the specified key algorithm from the specified provider.

Parameters:

algorithm - the standard name of the requested key algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

provider - the name of the provider.

Returns:

the new KeyGenerator object.

Throws:

NullPointerException - if the specified algorithm is null.

NoSuchAlgorithmException - if a key generator for the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

NoSuchProviderException - if the specified provider has not been configured.

IllegalArgumentException - if the provider is null.

getInstance

public static final KeyGenerator getInstance(String algorithm,
                                             Provider provider)
                                      throws NoSuchAlgorithmException,
                                             NoSuchProviderException

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

Parameters:

algorithm - the standard name of the requested key algorithm. See Appendix A in the Java Cryptography Extension Reference Guide for information about standard algorithm names.

provider - the provider.

Returns:

the new KeyGenerator object.

Throws:

NullPointerException - if the specified algorithm is null.

NoSuchAlgorithmException - if a key generator for the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

IllegalArgumentException - if the provider is null.

NoSuchProviderException

getProvider

public final Provider getProvider()

Returns the provider of this KeyGenerator object.

Returns:

the provider of this KeyGenerator object.

init

public final void init(SecureRandom random)

Initializes the key generator.

Parameters:

random - the source of randomness for this generator.

init

public final void init(AlgorithmParameterSpec params)
                throws InvalidAlgorithmParameterException

Initializes this key generator with the specified parameter set. If this key generator requires any random bytes, it will get them using the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

Parameters:

params - the key generation parameters.

Throws:

InvalidAlgorithmParameterException - if the given parameters are inappropriate for this key generator.

init

public final void init(AlgorithmParameterSpec params,
                       SecureRandom random)
                throws InvalidAlgorithmParameterException

Initializes the key generator with the specified parameter set and a user-provided source of randomness.

Parameters:

params - the key generation parameters.

random - the source of randomness for this key generator.

Throws:

InvalidAlgorithmParameterException - if params is inappropriate for this key generator.

init

public final void init(int keysize)

Initializes this key generator for a certain keysize. If this key generator requires any random bytes, it will get them using the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

Parameters:

keysize - the keysize. This is an algorithm-specific metric, specified in number of bits.

Throws:

InvalidAlgorithmParameterException - if params is inappropriate for this key generator

init

public final void init(int keysize,
                       SecureRandom random)

Initializes this key generator for a certain keysize, using the given source of randomness.

Parameters:

keysize - the keysize. This is an algorithm-specific metric, specified in number of bits.

random - the source of randomness for this key generator.

generateKey

public final SecretKey generateKey()

Generates a secret key.

Returns:

the new key.