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## javax.crypto
Class ExemptionMechanismSpi

    java.lang.Object
      javax.crypto.ExemptionMechanismSpi

public abstract class ExemptionMechanismSpi
extends Object

This class defines the Service Provider Interface (SPI) for the `ExemptionMechanism` class. All the abstract methods in this class must be implemented by each cryptographic service provider who wishes to supply the implementation of a particular exemption mechanism.

Since:
  1.4

Constructor Summary
`ExemptionMechanismSpi()`

Method Summary
`protected abstract byte[]` | `engineGenExemptionBlob()` Generates the exemption mechanism key blob.
`protected abstract int` | `engineGenExemptionBlob(byte[] output, int outputOffset)` Generates the exemption mechanism key blob, and stores the result in the `output` buffer, starting at `outputOffset` inclusive.
`protected abstract int` | `engineGetOutputSize(int inputLen)` Returns the length in bytes that an output buffer would need to be in order to hold the result of the next `engineGenExemptionBlob` operation, given the input length `inputLen` (in bytes).
`protected abstract void` | `engineInit(Key key)` Initializes this exemption mechanism with a key.
`protected abstract void` | `engineInit(Key key, AlgorithmParameters params)` Initializes this exemption mechanism with a key and a set of algorithm parameters.
`protected abstract void` | `engineInit(Key key, AlgorithmParameterSpec params)` Initializes this exemption mechanism with a key and a set of algorithm parameters.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ExemptionMechanismSpi

    public ExemptionMechanismSpi()

Method Detail

### engineGetOutputSize

    protected abstract int engineGetOutputSize(int inputLen)

  Returns the length in bytes that an output buffer would need to be in order to hold the result of the next `engineGenExemptionBlob` operation, given the input length `inputLen` (in bytes).

  The actual output length of the next `engineGenExemptionBlob` call may be smaller than the length returned by this method.

  Parameters:
    `inputLen` - the input length (in bytes)
  Returns:
    the required output buffer size (in bytes)

### engineInit

    protected abstract void engineInit(Key key)
                                throws InvalidKeyException,
                                       ExemptionMechanismException

  Initializes this exemption mechanism with a key.

  If this exemption mechanism requires any algorithm parameters that cannot be derived from the given `key`, the underlying exemption mechanism implementation is supposed to generate the required parameters itself (using provider-specific default values); in the case that algorithm parameters must be specified by the caller, an `InvalidKeyException` is raised.

  Parameters:
    `key` - the key for this exemption mechanism
  Throws:
    `InvalidKeyException` - if the given key is inappropriate for this exemption mechanism.
    `ExemptionMechanismException` - if problem(s) encountered in the process of initializing.

### engineInit

    protected abstract void engineInit(Key key,
                                       AlgorithmParameterSpec params)
                                throws InvalidKeyException,
                                       InvalidAlgorithmParameterException,
                                       ExemptionMechanismException

  Initializes this exemption mechanism with a key and a set of algorithm parameters.

  If this exemption mechanism requires any algorithm parameters and `params` is null, the underlying exemption mechanism implementation is supposed to generate the required parameters itself (using provider-specific default values); in the case that algorithm parameters must be specified by the caller, an `InvalidAlgorithmParameterException` is raised.

  Parameters:
    `key` - the key for this exemption mechanism
    `params` - the algorithm parameters
  Throws:
    `InvalidKeyException` - if the given key is inappropriate for this exemption mechanism.
    `InvalidAlgorithmParameterException` - if the given algorithm parameters are inappropriate for this exemption mechanism.
    `ExemptionMechanismException` - if problem(s) encountered in the process of initializing.

### engineInit

    protected abstract void engineInit(Key key,
                                       AlgorithmParameters params)
                                throws InvalidKeyException,
                                       InvalidAlgorithmParameterException,
                                       ExemptionMechanismException

  Initializes this exemption mechanism with a key and a set of algorithm parameters.

  If this exemption mechanism requires any algorithm parameters and `params` is null, the underlying exemption mechanism implementation is supposed to generate the required parameters itself (using provider-specific default values); in the case that algorithm parameters must be specified by the caller, an `InvalidAlgorithmParameterException` is raised.

  Parameters:
    `key` - the key for this exemption mechanism
    `params` - the algorithm parameters
  Throws:
    `InvalidKeyException` - if the given key is inappropriate for this exemption mechanism.
    `InvalidAlgorithmParameterException` - if the given algorithm parameters are inappropriate for this exemption mechanism.
    `ExemptionMechanismException` - if problem(s) encountered in the process of initializing.

### engineGenExemptionBlob

    protected abstract byte[] engineGenExemptionBlob()
                                              throws ExemptionMechanismException

  Generates the exemption mechanism key blob.

  Returns:
    the new buffer with the result key blob.
  Throws:
    `ExemptionMechanismException` - if problem(s) encountered in the process of generating.

### engineGenExemptionBlob

    protected abstract int engineGenExemptionBlob(byte[] output,
                                                  int outputOffset)
                                           throws ShortBufferException,
                                                  ExemptionMechanismException

  Generates the exemption mechanism key blob, and stores the result in the `output` buffer, starting at `outputOffset` inclusive.

  If the `output` buffer is too small to hold the result, a `ShortBufferException` is thrown. In this case, repeat this call with a larger output buffer. Use `engineGetOutputSize` to determine how big the output buffer should be.

  Parameters:
    `output` - the buffer for the result
    `outputOffset` - the offset in `output` where the result is stored
  Returns:
    the number of bytes stored in `output`
  Throws:
    `ShortBufferException` - if the given output buffer is too small to hold the result.
    `ExemptionMechanismException` - if problem(s) encountered in the process of generating.

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