# Class KeyPairGeneratorSpi

java.lang.Object
java.security.KeyPairGeneratorSpi

Direct Known Subclasses:
  `KeyPairGenerator`

public abstract class KeyPairGeneratorSpi extends Object

This class defines the Service Provider Interface (SPI) for the `KeyPairGenerator` class, which is used to generate pairs of public and private keys.

All the abstract methods in this class must be implemented by each cryptographic service provider who wishes to supply the implementation of a key pair generator for a particular algorithm.

In case the client does not explicitly initialize the `KeyPairGenerator` (via a call to an `initialize` method), each provider must supply (and document) a default initialization. See the Keysize Restriction sections of the JDK Providers document for information on the KeyPairGenerator 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 `KeyPairGenerator` instead of relying on provider-specific defaults.

Since:
  1.2
See Also:
  - `KeyPairGenerator`
  - `AlgorithmParameterSpec`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `KeyPairGeneratorSpi()`
  Constructor for subclasses to call.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract KeyPair`
  `generateKeyPair()`
  Generates a key pair.
  `abstract void`
  `initialize(int keysize, SecureRandom random)`
  Initializes the key pair generator for a certain keysize, using the default parameter set.
  `void`
  `initialize(AlgorithmParameterSpec params, SecureRandom random)`
  Initializes the key pair generator using the specified parameter set and user-provided source of randomness.

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### KeyPairGeneratorSpi

    public KeyPairGeneratorSpi()
    Constructor for subclasses to call.

- ## Method Details

  - ### initialize

    public abstract void initialize(int keysize, SecureRandom random)
    Initializes the key pair generator for a certain keysize, using the default parameter set.
    Parameters:
      `keysize` - the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.
      `random` - the source of randomness for this generator.
    Throws:
      `InvalidParameterException` - if the `keysize` is not supported by this `KeyPairGeneratorSpi` object.

  - ### initialize

    public void initialize(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException
    Initializes the key pair generator using the specified parameter set and user-provided source of randomness.

    This concrete method has been added to this previously-defined abstract class. (For backwards compatibility, it cannot be abstract.) It may be overridden by a provider to initialize the key pair generator. Such an override is expected to throw an `InvalidAlgorithmParameterException` if a parameter is inappropriate for this key pair generator. If this method is not overridden, it always throws an `UnsupportedOperationException`.

    Parameters:
      `params` - the parameter set used to generate the keys.
      `random` - the source of randomness for this generator.
    Throws:
      `InvalidAlgorithmParameterException` - if the given parameters are inappropriate for this key pair generator.
    Since:
      1.2

  - ### generateKeyPair

    public abstract KeyPair generateKeyPair()
    Generates a key pair. Unless an initialization method is called using a KeyPairGenerator interface, algorithm-specific defaults will be used. This will generate a new key pair every time it is called.
    Returns:
      the newly generated `KeyPair`