KeyGenerator

public class KeyGenerator extends Object

This class provides the functionality of a secret (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.

Android provides the following KeyGenerator algorithms:

Algorithm	Supported API Levels
AES	1+
AESWRAP	1-8
ARC4	14+
BLOWFISH	10+
ChaCha20	28+
DES	1+
DESede	1+
DESedeWRAP	1-8
HmacMD5	1+
HmacSHA1	11+
HmacSHA224	1-8,22+
HmacSHA256	1+
HmacSHA384	1+
HmacSHA512	1+
RC4	10-13

These algorithms are described in the KeyGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

See Also

• SecretKey

Protected Constructor Summary

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

Public Method Summary

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

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Protected Constructors

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

Creates a KeyGenerator object.

Parameters

keyGenSpi	the delegate
provider	the provider
algorithm	the algorithm

Public Methods

public final SecretKey generateKey ()

Generates a secret key.

Returns

• the new key

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.

public static final KeyGenerator getInstance (String algorithm)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Returns

• the new KeyGenerator object.

Throws

NullPointerException	if the specified algorithm is null.
NoSuchAlgorithmException	if no Provider supports a KeyGeneratorSpi implementation for the specified algorithm.

See Also

• Provider

public static final KeyGenerator getInstance (String algorithm, String provider)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 standard name of the requested key algorithm. See the KeyGenerator 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 KeyGenerator object.

Throws

NullPointerException	if the specified algorithm is null.
NoSuchAlgorithmException	if a KeyGeneratorSpi 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 is null or empty.

See Also

• Provider

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

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation 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 KeyGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException	if the provider is null.

See Also

• Provider

public final Provider getProvider ()

Returns the provider of this KeyGenerator object.

Returns

• the provider of this KeyGenerator object

public final void init (AlgorithmParameterSpec params, SecureRandom random)

Initializes this 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

public final void init (SecureRandom random)

Initializes this key generator.

Parameters

random	the source of randomness for this generator

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

InvalidParameterException	if the keysize is wrong or not supported.

public final void init (int keysize, SecureRandom random)

Initializes this key generator for a certain keysize, using a user-provided 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

Throws

InvalidParameterException	if the keysize is wrong or not supported.

public final void init (AlgorithmParameterSpec params)

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