# 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

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

## Method Summary

Modifier and Type
Method
Description
`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 declared in class Object

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

## Constructor Details

### ExemptionMechanismSpi

public ExemptionMechanismSpi()
Constructor for subclasses to call.

## Method Details

### 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.