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Class ExemptionMechanism

public class ExemptionMechanism
extends Object

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.

Since:
1.4

Constructors

ExemptionMechanism

protected ExemptionMechanism(ExemptionMechanismSpi exmechSpi,
                             Provider provider,
                             String mechanism)

Creates a ExemptionMechanism object.

Parameters:
exmechSpi - the delegate
provider - the provider
mechanism - the exemption mechanism

Methods

getName

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:
the exemption mechanism name of this ExemptionMechanism object.

getInstance

public static final ExemptionMechanism getInstance(String algorithm)
                                            throws NoSuchAlgorithmException

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 - 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:
the new ExemptionMechanism object.
Throws:
NullPointerException - if algorithm is null.
NoSuchAlgorithmException - if no Provider supports an ExemptionMechanismSpi implementation for the specified algorithm.
See Also:
Provider

getInstance

public static final ExemptionMechanism getInstance(String algorithm,
                                                   String provider)
                                            throws NoSuchAlgorithmException,
                                                   NoSuchProviderException

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 - 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 - the name of the provider.
Returns:
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:
Provider

getInstance

public static final ExemptionMechanism getInstance(String algorithm,
                                                   Provider provider)
                                            throws NoSuchAlgorithmException

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 - 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 - the provider.
Returns:
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:
Provider

getProvider

public final Provider getProvider()

Returns the provider of this ExemptionMechanism object.

Returns:
the provider of this ExemptionMechanism object.

isCryptoAllowed

public final boolean isCryptoAllowed(Key key)
                              throws ExemptionMechanismException

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 - the key the crypto is going to use.
Returns:
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.

getOutputSize

public final int getOutputSize(int inputLen)
                        throws IllegalStateException

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 - the input length (in bytes)
Returns:
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)

init

public final void init(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.

init

public final void init(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.

init

public final void init(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.

genExemptionBlob

public final byte[] genExemptionBlob()
                              throws IllegalStateException,
                                     ExemptionMechanismException

Generates the exemption mechanism key blob.

Returns:
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

public final int genExemptionBlob(byte[] output)
                           throws IllegalStateException,
                                  ShortBufferException,
                                  ExemptionMechanismException

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 - the buffer for the result
Returns:
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

public final int genExemptionBlob(byte[] output,
                                  int outputOffset)
                           throws IllegalStateException,
                                  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 getOutputSize 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:
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.

finalize

protected void finalize()

Ensures that the key stored away by this ExemptionMechanism object will be wiped out when there are no more references to it.

Overrides:
finalize in class Object
See Also:
WeakReference, PhantomReference

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