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ExemptionMechanism

public class ExemptionMechanism
extends Object

java.lang.Object
   ↳ javax.crypto.ExemptionMechanism


This class provides the functionality of an exemption mechanism, examples of which are key recovery, key weakening, and key escrow.

Applications or applets that use an exemption mechanism may be granted stronger encryption capabilities than those which don't.

Summary

Protected constructors

ExemptionMechanism(ExemptionMechanismSpi exmechSpi, Provider provider, String mechanism)

Creates a ExemptionMechanism object.

Public methods

final int genExemptionBlob(byte[] output)

Generates the exemption mechanism key blob, and stores the result in the output buffer.

final byte[] genExemptionBlob()

Generates the exemption mechanism key blob.

final int genExemptionBlob(byte[] output, int outputOffset)

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

static final ExemptionMechanism getInstance(String algorithm)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

static final ExemptionMechanism getInstance(String algorithm, String provider)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

static final ExemptionMechanism getInstance(String algorithm, Provider provider)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

final String getName()

Returns the exemption mechanism name of this ExemptionMechanism object.

final int getOutputSize(int inputLen)

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

final Provider getProvider()

Returns the provider of this ExemptionMechanism object.

final void init(Key key, AlgorithmParameters params)

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

final void init(Key key, AlgorithmParameterSpec params)

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

final void init(Key key)

Initializes this exemption mechanism with a key.

final boolean isCryptoAllowed(Key key)

Returns whether the result blob has been generated successfully by this exemption mechanism.

Inherited methods

Protected constructors

ExemptionMechanism

added in API level 1
protected ExemptionMechanism (ExemptionMechanismSpi exmechSpi, 
                Provider provider, 
                String mechanism)

Creates a ExemptionMechanism object.

Parameters
exmechSpi ExemptionMechanismSpi: the delegate

provider Provider: the provider

mechanism String: the exemption mechanism

Public methods

genExemptionBlob

added in API level 1
public final int genExemptionBlob (byte[] output)

Generates the exemption mechanism key blob, and stores the result in the output buffer.

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 getOutputSize to determine how big the output buffer should be.

Parameters
output byte: the buffer for the result

Returns
int the number of bytes stored in output

Throws
IllegalStateException if this exemption mechanism is in a wrong state (e.g., has not been initialized).
ShortBufferException if the given output buffer is too small to hold the result.
ExemptionMechanismException if problem(s) encountered in the process of generating.

genExemptionBlob

added in API level 1
public final byte[] genExemptionBlob ()

Generates the exemption mechanism key blob.

Returns
byte[] the new buffer with the result key blob.

Throws
IllegalStateException if this exemption mechanism is in a wrong state (e.g., has not been initialized).
ExemptionMechanismException if problem(s) encountered in the process of generating.

genExemptionBlob

added in API level 1
public final int genExemptionBlob (byte[] output, 
                int outputOffset)

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 getOutputSize to determine how big the output buffer should be.

Parameters
output byte: the buffer for the result

outputOffset int: the offset in output where the result is stored

Returns
int the number of bytes stored in output

Throws
IllegalStateException if this exemption mechanism is in a wrong state (e.g., has not been initialized).
ShortBufferException if the given output buffer is too small to hold the result.
ExemptionMechanismException if problem(s) encountered in the process of generating.

getInstance

added in API level 1
public static final ExemptionMechanism getInstance (String algorithm)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new ExemptionMechanism object encapsulating the ExemptionMechanismSpi 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.

Parameters
algorithm String: the standard name of the requested exemption mechanism. See the ExemptionMechanism section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard exemption mechanism names.

Returns
ExemptionMechanism the new ExemptionMechanism object.

Throws
NullPointerException if algorithm is null.
NoSuchAlgorithmException if no Provider supports an ExemptionMechanismSpi implementation for the specified algorithm.

See also:

getInstance

added in API level 1
public static final ExemptionMechanism getInstance (String algorithm, 
                String provider)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

A new ExemptionMechanism object encapsulating the ExemptionMechanismSpi 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 String: the standard name of the requested exemption mechanism. See the ExemptionMechanism section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard exemption mechanism names.

provider String: the name of the provider.

Returns
ExemptionMechanism the new ExemptionMechanism object.

Throws
NullPointerException if algorithm is null.
NoSuchAlgorithmException if an ExemptionMechanismSpi 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.
IllegalArgumentException if the provider is null or empty.

See also:

getInstance

added in API level 1
public static final ExemptionMechanism getInstance (String algorithm, 
                Provider provider)

Returns an ExemptionMechanism object that implements the specified exemption mechanism algorithm.

A new ExemptionMechanism object encapsulating the ExemptionMechanismSpi 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 String: the standard name of the requested exemption mechanism. See the ExemptionMechanism section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard exemption mechanism names.

provider Provider: the provider.

Returns
ExemptionMechanism the new ExemptionMechanism object.

Throws
NullPointerException if algorithm is null.
NoSuchAlgorithmException if an ExemptionMechanismSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException if the provider is null.

See also:

getName

added in API level 1
public final String getName ()

Returns the exemption mechanism name of this ExemptionMechanism object.

This is the same name that was specified in one of the getInstance calls that created this ExemptionMechanism object.

Returns
String the exemption mechanism name of this ExemptionMechanism object.

getOutputSize

added in API level 1
public final int getOutputSize (int inputLen)

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

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

Parameters
inputLen int: the input length (in bytes)

Returns
int the required output buffer size (in bytes)

Throws
IllegalStateException if this exemption mechanism is in a wrong state (e.g., has not yet been initialized)

getProvider

added in API level 1
public final Provider getProvider ()

Returns the provider of this ExemptionMechanism object.

Returns
Provider the provider of this ExemptionMechanism object.

init

added in API level 1
public final void init (Key key, 
                AlgorithmParameters params)

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 Key: the key for this exemption mechanism

params AlgorithmParameters: 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.

init

added in API level 1
public final void init (Key key, 
                AlgorithmParameterSpec params)

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 Key: the key for this exemption mechanism

params AlgorithmParameterSpec: 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.

init

added in API level 1
public final void init (Key key)

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 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.

isCryptoAllowed

added in API level 1
public final boolean isCryptoAllowed (Key key)

Returns whether the result blob has been generated successfully by this exemption mechanism.

The method also makes sure that the key passed in is the same as the one this exemption mechanism used in initializing and generating phases.

Parameters
key Key: the key the crypto is going to use.

Returns
boolean whether the result blob of the same key has been generated successfully by this exemption mechanism; false if key is null.

Throws
ExemptionMechanismException if problem(s) encountered while determining whether the result blob has been generated successfully by this exemption mechanism object.