# Class KeyGenerator

java.lang.Object
javax.crypto.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, 256)
- `ChaCha20`
- `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
External Specifications
  - Java Security Standard Algorithm Names
See Also:
  - `SecretKey`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)`
  Creates a `KeyGenerator` object.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `final SecretKey`
  `generateKey()`
  Generates a secret key.
  `final String`
  `getAlgorithm()`
  Returns the algorithm name of this `KeyGenerator` object.
  `static final KeyGenerator`
  `getInstance(String algorithm)`
  Returns a `KeyGenerator` object that generates secret keys for the specified algorithm.
  `static final KeyGenerator`
  `getInstance(String algorithm, String provider)`
  Returns a `KeyGenerator` object that generates secret keys for the specified algorithm.
  `static final 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(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(SecureRandom random)`
  Initializes this key generator.
  `final void`
  `init(AlgorithmParameterSpec params)`
  Initializes this key generator with the specified parameter set.
  `final 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 Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `protected Object`
  `clone()`
  Creates and returns a copy of this object.
  `boolean`
  `equals(Object obj)`
  Indicates whether some other object is "equal to" this one.
  `protected void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization is deprecated and subject to removal in a future release.
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `int`
  `hashCode()`
  Returns a hash code value for this object.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `String`
  `toString()`
  Returns a string representation of the object.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## Constructor Details

  - ### KeyGenerator

    protected KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)
    Creates a `KeyGenerator` object.
    Parameters:
      `keyGenSpi` - the delegate
      `provider` - the provider
      `algorithm` - the algorithm

- ## Method Details

  - ### 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 from 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`
    External Specifications
      - Java Security Standard Algorithm Names
    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`
    External Specifications
      - Java Security Standard Algorithm Names
    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`
    External Specifications
      - Java Security Standard Algorithm Names
    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