KeyFactorySpi (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.security, class: KeyFactorySpi
Keywords: java.security.KeyFactorySpi class

# Class KeyFactorySpi

java.lang.Object
java.security.KeyFactorySpi

public abstract class KeyFactorySpi extends Object
This class defines the Service Provider Interface (SPI) for the `KeyFactory` class. All the abstract methods in this class must be implemented by each cryptographic service provider who wishes to supply the implementation of a key factory for a particular algorithm.

Key factories are used to convert keys (opaque cryptographic keys of type `Key`) into key specifications (transparent representations of the underlying key material), and vice versa.

Key factories are bidirectional. That is, they allow you to build an opaque key object from a given key specification (key material), or to retrieve the underlying key material of a key object in a suitable format.

Multiple compatible key specifications may exist for the same key. For example, a DSA public key may be specified using `DSAPublicKeySpec` or `X509EncodedKeySpec`. A key factory can be used to translate between compatible key specifications.

A provider should document all the key specifications supported by its key factory.

Since:
  1.2
See Also:
  - `KeyFactory`
  - `Key`
  - `PublicKey`
  - `PrivateKey`
  - `KeySpec`
  - `DSAPublicKeySpec`
  - `X509EncodedKeySpec`

- ## Constructor Summary

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

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected abstract PrivateKey`
  `engineGeneratePrivate(KeySpec keySpec)`
  Generates a private key object from the provided key specification (key material).
  `protected abstract PublicKey`
  `engineGeneratePublic(KeySpec keySpec)`
  Generates a public key object from the provided key specification (key material).
  `protected abstract <T extends KeySpec>
  T`
  `engineGetKeySpec(Key key, Class<T> keySpec)`
  Returns a specification (key material) of the given key object.
  `protected abstract Key`
  `engineTranslateKey(Key key)`
  Translates a key object, whose provider may be unknown or potentially untrusted, into a corresponding key object of this key factory.

  ### 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

  - ### KeyFactorySpi

    public KeyFactorySpi()
    Constructor for subclasses to call.

- ## Method Details

  - ### engineGeneratePublic

    protected abstract PublicKey engineGeneratePublic(KeySpec keySpec) throws InvalidKeySpecException
    Generates a public key object from the provided key specification (key material).
    Parameters:
      `keySpec` - the specification (key material) of the public key.
    Returns:
      the public key.
    Throws:
      `InvalidKeySpecException` - if the given key specification is inappropriate for this key factory to produce a public key.

  - ### engineGeneratePrivate

    protected abstract PrivateKey engineGeneratePrivate(KeySpec keySpec) throws InvalidKeySpecException
    Generates a private key object from the provided key specification (key material).
    Parameters:
      `keySpec` - the specification (key material) of the private key.
    Returns:
      the private key.
    Throws:
      `InvalidKeySpecException` - if the given key specification is inappropriate for this key factory to produce a private key.

  - ### engineGetKeySpec

    protected abstract <T extends KeySpec> T engineGetKeySpec(Key key, Class<T> keySpec) throws InvalidKeySpecException
    Returns a specification (key material) of the given key object. `keySpec` identifies the specification class in which the key material should be returned. It could, for example, be `DSAPublicKeySpec.class`, to indicate that the key material should be returned in an instance of the `DSAPublicKeySpec` class.
    Type Parameters:
      `T` - the type of the key specification to be returned
    Parameters:
      `key` - the key.
      `keySpec` - the specification class in which the key material should be returned.
    Returns:
      the underlying key specification (key material) in an instance of the requested specification class.
    Throws:
      `InvalidKeySpecException` - if the requested key specification is inappropriate for the given key, or the given key cannot be dealt with (e.g., the given key has an unrecognized format).

  - ### engineTranslateKey

    protected abstract Key engineTranslateKey(Key key) throws InvalidKeyException
    Translates a key object, whose provider may be unknown or potentially untrusted, into a corresponding key object of this key factory.
    Parameters:
      `key` - the key whose provider is unknown or untrusted.
    Returns:
      the translated key.
    Throws:
      `InvalidKeyException` - if the given key cannot be processed by this key factory.