Class 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. See the Keysize Restriction sections of the JDK Providers document for information on the KeyGenerator defaults used by JDK providers. However, note that defaults may vary across different providers. Additionally, the default value for a provider may change in a future version. Therefore, it is recommended to explicitly initialize the KeyGenerator instead of relying on provider-specific defaults.

Every implementation of the Java platform is required to support the following standard KeyGenerator algorithms with the keysizes in parentheses:

  • AES (128)
  • DES (56)
  • DESede (168)
  • HmacSHA1
  • HmacSHA256
These algorithms are described in the KeyGenerator section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.
Since:
1.4
See Also:
SecretKey

Constructors

Modifier Constructor Description
protected KeyGenerator​(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)

Creates a KeyGenerator object.

Methods

Modifier and Type Method Description
SecretKey generateKey()

Generates a secret key.
String getAlgorithm()

Returns the algorithm name of this KeyGenerator object.
static KeyGenerator getInstance​(String algorithm)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
static KeyGenerator getInstance​(String algorithm, String provider)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
static KeyGenerator getInstance​(String algorithm, Provider provider)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
Provider getProvider()

Returns the provider of this KeyGenerator object.
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 a user-provided source of randomness.
void init​(SecureRandom random)

Initializes this key generator.
void init​(AlgorithmParameterSpec params)

Initializes this key generator with the specified parameter set.
void init​(AlgorithmParameterSpec params, SecureRandom random)

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

Methods declared in class java.lang.Object

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

Constructors

KeyGenerator

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

Creates a KeyGenerator object.

Parameters:
keyGenSpi - the delegate
provider - the provider
algorithm - the algorithm

Methods

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

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.

Implementation Note:
The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Parameters:
algorithm - the standard name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
Returns:
the new KeyGenerator object
Throws:
NoSuchAlgorithmException - if no Provider supports a KeyGeneratorSpi implementation for the specified algorithm
NullPointerException - if algorithm is null
See Also:
Provider

getInstance

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

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 Security Standard Algorithm Names Specification for information about standard algorithm names.
provider - the name of the provider.
Returns:
the new KeyGenerator object
Throws:
IllegalArgumentException - if the provider is null or empty
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
NullPointerException - if algorithm is null
See Also:
Provider

getInstance

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

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 Security Standard Algorithm Names Specification for information about standard algorithm names.
provider - the provider.
Returns:
the new KeyGenerator object
Throws:
IllegalArgumentException - if the provider is null
NoSuchAlgorithmException - if a KeyGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object
NullPointerException - if algorithm is null
See Also:
Provider

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 this 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 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

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:
InvalidParameterException - if the keysize is wrong or not supported.

init

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.

generateKey

public final SecretKey generateKey()

Generates a secret key.

Returns:
the new key

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Documentation extracted from Debian's OpenJDK Development Kit package.
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