javax.crypto
Class KeyGenerator

java.lang.Object
  |
  +--javax.crypto.KeyGenerator

public class KeyGenerator
extends java.lang.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 initialisation of the object:

Algorithm-Independent Initialisation

All key generators share the concepts of a "strength" and a source of randomness. The measure of strength is universally shared by all algorithms, though it is interpreted differently for different algorithms. 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 strength argument, and uses a system-provided source of randomness, 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 Initialisation

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 source of randomness is system-provided for the other.

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

See Also:
SecretKey

Field Summary
static java.lang.String ident
           
 
Constructor Summary
protected KeyGenerator(KeyGeneratorSpi spi, java.security.Provider provider, java.lang.String algorithm)
          Creates a KeyGenerator object using the given provider, KeyGeneratorSpi and for the specified algorithm.
 
Method Summary
 SecretKey generateKey()
          Generates a secret key.
 java.lang.String getAlgorithm()
          Returns the algorithm name of this KeyGenerator object.
static KeyGenerator getInstance(java.lang.String algorithm)
          Generates a KeyGenerator object for the specified algorithm.
static KeyGenerator getInstance(java.lang.String algorithm, java.lang.String provider)
          Generates a KeyGenerator object for the specified key algorithm from the specified provider.
 java.security.Provider getProvider()
          Returns the provider of this KeyGenerator object.
 void init(java.security.spec.AlgorithmParameterSpec params)
          Initialises the key generator with the specified parameter set, using a system-provided source of randomness.
 void init(java.security.spec.AlgorithmParameterSpec params, java.security.SecureRandom random)
          Initialises the key generator with the specified parameter set and a user-provided source of randomness.
 void init(int strength)
          Initialises this key generator for a certain strength, using a system-provided source of randomness.
 void init(int strength, java.security.SecureRandom random)
          Initialises this key generator for a certain strength, using a user-provided source of randomness.
 void init(java.security.SecureRandom random)
          Initialises the key generator.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

ident

public static final java.lang.String ident
Constructor Detail

KeyGenerator

protected KeyGenerator(KeyGeneratorSpi spi,
                       java.security.Provider provider,
                       java.lang.String algorithm)
Creates a KeyGenerator object using the given provider, KeyGeneratorSpi and for the specified algorithm.
Parameters:
spi - the KeyGeneratorSpi to use
provider - the provider to use
algorithm - the standard name of the key algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.
Method Detail

getAlgorithm

public final java.lang.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 KeyGenerator getInstance(java.lang.String algorithm)
                                throws java.security.NoSuchAlgorithmException
Generates a KeyGenerator object for the specified algorithm. 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 API Specification & Reference for information about standard algorithm names.
Returns:
the new KeyGenerator object
Throws:
java.security.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 KeyGenerator getInstance(java.lang.String algorithm,
                                       java.lang.String provider)
                                throws java.security.NoSuchAlgorithmException,
                                       java.security.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 API Specification & Reference for information about standard algorithm names.
provider - the name of the provider
Throws:
java.security.NoSuchAlgorithmException - if a key generator for the requested algorithm is not available.
java.security.NoSuchProviderException - if the requested provider is not available
See Also:
Provider

getProvider

public final java.security.Provider getProvider()
Returns the provider of this KeyGenerator object.
Returns:
the provider of this KeyGenerator object

init

public final void init(java.security.SecureRandom random)
Initialises the key generator.
Parameters:
random - the source of randomness for this generator.

init

public final void init(java.security.spec.AlgorithmParameterSpec params)
                throws java.security.InvalidAlgorithmParameterException
Initialises the key generator with the specified parameter set, using a system-provided source of randomness.
Parameters:
params - the key generation parameters
Throws:
java.security.InvalidAlgorithmParameterException - if the given parameters are inappropriate for this key generator.

init

public final void init(java.security.spec.AlgorithmParameterSpec params,
                       java.security.SecureRandom random)
                throws java.security.InvalidAlgorithmParameterException
Initialises 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:
java.security.InvalidAlgorithmParameterException - if params is inappropriate for this key generator.

init

public final void init(int strength)
Initialises this key generator for a certain strength, using a system-provided source of randomness.
Parameters:
strength - the strength of the key. This is an algorithm-specific metric specified in number of bits.

init

public final void init(int strength,
                       java.security.SecureRandom random)
Initialises this key generator for a certain strength, using a user-provided source of randomness.
Parameters:
strength - the strength of the key. This is an algorithm-specific metric specified in number of bits.
random - the source of randomness for this key generator

generateKey

public SecretKey generateKey()
Generates a secret key.
Returns:
the new key