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 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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package javax.crypto;

import java.security.AlgorithmParameters;
import java.security.Provider;
import java.security.Key;
import java.security.Security;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.InvalidKeyException;
import java.security.InvalidAlgorithmParameterException;
import java.security.spec.AlgorithmParameterSpec;

import sun.security.jca.GetInstance.Instance;


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
/**
 * This class provides the functionality of an exemption mechanism, examples
 * of which are <i>key recovery</i>, <i>key weakening</i>, and
 * <i>key escrow</i>.
 *
 * <p>Applications or applets that use an exemption mechanism may be granted
 * stronger encryption capabilities than those which don't.
 *
 * @since 1.4
 */

public class ExemptionMechanism {

    // The provider
    private Provider provider;

    // The provider implementation (delegate)
    private ExemptionMechanismSpi exmechSpi;

    // The name of the exemption mechanism.
    private String mechanism;

    // Flag which indicates whether this ExemptionMechanism
    // result is generated successfully.
    private boolean done = false;

    // State information
    private boolean initialized = false;

    // Store away the key at init() time for later comparison.
    private Key keyStored = null;

    
Creates a ExemptionMechanism object.

Params:
  • exmechSpi – the delegate
  • provider – the provider
  • mechanism – the exemption mechanism
/**
     * Creates a ExemptionMechanism object.
     *
     * @param exmechSpi the delegate
     * @param provider the provider
     * @param mechanism the exemption mechanism
     */
    protected ExemptionMechanism(ExemptionMechanismSpi exmechSpi,
                                 Provider provider,
                                 String mechanism) {
        this.exmechSpi = exmechSpi;
        this.provider = provider;
        this.mechanism = mechanism;
    }

    
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.
/**
     * Returns the exemption mechanism name of this
     * <code>ExemptionMechanism</code> object.
     *
     * <p>This is the same name that was specified in one of the
     * <code>getInstance</code> calls that created this
     * <code>ExemptionMechanism</code> object.
     *
     * @return the exemption mechanism name of this
     * <code>ExemptionMechanism</code> object.
     */
    public final String getName() {
        return this.mechanism;
    }

    
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. 
Params:
Throws:
See Also:
Returns:the new ExemptionMechanism object.
/**
     * Returns an <code>ExemptionMechanism</code> object that implements the
     * specified exemption mechanism algorithm.
     *
     * <p> 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.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * @param algorithm the standard name of the requested exemption
     * mechanism.
     * See the ExemptionMechanism section in the
     * <a href=
     *   "{@docRoot}/../technotes/guides/security/StandardNames.html#Exemption">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard exemption mechanism names.
     *
     * @return the new <code>ExemptionMechanism</code> object.
     *
     * @exception NullPointerException if <code>algorithm</code>
     *          is null.
     *
     * @exception NoSuchAlgorithmException if no Provider supports an
     *          ExemptionMechanismSpi implementation for the
     *          specified algorithm.
     *
     * @see java.security.Provider
     */
    public static final ExemptionMechanism getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Instance instance = JceSecurity.getInstance("ExemptionMechanism",
                ExemptionMechanismSpi.class, algorithm);
        return new ExemptionMechanism((ExemptionMechanismSpi)instance.impl,
                instance.provider, algorithm);
    }


    
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. 
Params:
Throws:
See Also:
Returns:the new ExemptionMechanism object.
/**
     * Returns an <code>ExemptionMechanism</code> object that implements the
     * specified exemption mechanism algorithm.
     *
     * <p> 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.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.

     * @param algorithm the standard name of the requested exemption mechanism.
     * See the ExemptionMechanism section in the
     * <a href=
     *   "{@docRoot}/../technotes/guides/security/StandardNames.html#Exemption">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard exemption mechanism names.
     *
     * @param provider the name of the provider.
     *
     * @return the new <code>ExemptionMechanism</code> object.
     *
     * @exception NullPointerException if <code>algorithm</code>
     *          is null.
     *
     * @exception NoSuchAlgorithmException if an ExemptionMechanismSpi
     *          implementation for the specified algorithm is not
     *          available from the specified provider.
     *
     * @exception NoSuchProviderException if the specified provider is not
     *          registered in the security provider list.
     *
     * @exception IllegalArgumentException if the <code>provider</code>
     *          is null or empty.
     *
     * @see java.security.Provider
     */
    public static final ExemptionMechanism getInstance(String algorithm,
            String provider) throws NoSuchAlgorithmException,
            NoSuchProviderException {
        Instance instance = JceSecurity.getInstance("ExemptionMechanism",
                ExemptionMechanismSpi.class, algorithm, provider);
        return new ExemptionMechanism((ExemptionMechanismSpi)instance.impl,
                instance.provider, algorithm);
    }

    
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.

Params:
Throws:
See Also:
Returns:the new ExemptionMechanism object.
/**
     * Returns an <code>ExemptionMechanism</code> object that implements the
     * specified exemption mechanism algorithm.
     *
     * <p> 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.
     *
     * @param algorithm the standard name of the requested exemption mechanism.
     * See the ExemptionMechanism section in the
     * <a href=
     *   "{@docRoot}/../technotes/guides/security/StandardNames.html#Exemption">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard exemption mechanism names.
     *
     * @param provider the provider.
     *
     * @return the new <code>ExemptionMechanism</code> object.
     *
     * @exception NullPointerException if <code>algorithm</code>
     *          is null.
     *
     * @exception NoSuchAlgorithmException if an ExemptionMechanismSpi
     *          implementation for the specified algorithm is not available
     *          from the specified Provider object.
     *
     * @exception IllegalArgumentException if the <code>provider</code>
     *          is null.
     *
     * @see java.security.Provider
     */
    public static final ExemptionMechanism getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Instance instance = JceSecurity.getInstance("ExemptionMechanism",
                ExemptionMechanismSpi.class, algorithm, provider);
        return new ExemptionMechanism((ExemptionMechanismSpi)instance.impl,
                instance.provider, algorithm);
    }

    
Returns the provider of this ExemptionMechanism object.

Returns:the provider of this ExemptionMechanism object.
/**
     * Returns the provider of this <code>ExemptionMechanism</code> object.
     *
     * @return the provider of this <code>ExemptionMechanism</code> object.
     */
    public final Provider getProvider() {
        return this.provider;
    }

    
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.

Params:
  • key – the key the crypto is going to use.
Throws:
  • ExemptionMechanismException – if problem(s) encountered
while determining whether the result blob has been generated successfully
by this exemption mechanism object.
Returns:whether the result blob of the same key has been generated
successfully by this exemption mechanism; false if key
is null.
/**
     * Returns whether the result blob has been generated successfully by this
     * exemption mechanism.
     *
     * <p>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.
     *
     * @param key the key the crypto is going to use.
     *
     * @return whether the result blob of the same key has been generated
     * successfully by this exemption mechanism; false if <code>key</code>
     * is null.
     *
     * @exception ExemptionMechanismException if problem(s) encountered
     * while determining whether the result blob has been generated successfully
     * by this exemption mechanism object.
     */
    public final boolean isCryptoAllowed(Key key)
            throws ExemptionMechanismException {
        boolean ret = false;
        if (done && (key != null)) {
            // Check if the key passed in is the same as the one
            // this exemption mechanism used.
            ret = keyStored.equals(key);
        }
        return ret;
     }

    
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. 
Params:
  • inputLen – the input length (in bytes)
Throws:
  • IllegalStateException – if this exemption mechanism is in a
wrong state (e.g., has not yet been initialized)
Returns:the required output buffer size (in bytes)
/**
     * Returns the length in bytes that an output buffer would need to be in
     * order to hold the result of the next
     * {@link #genExemptionBlob(byte[]) genExemptionBlob}
     * operation, given the input length <code>inputLen</code> (in bytes).
     *
     * <p>The actual output length of the next
     * {@link #genExemptionBlob(byte[]) genExemptionBlob}
     * call may be smaller than the length returned by this method.
     *
     * @param inputLen the input length (in bytes)
     *
     * @return the required output buffer size (in bytes)
     *
     * @exception IllegalStateException if this exemption mechanism is in a
     * wrong state (e.g., has not yet been initialized)
     */
    public final int getOutputSize(int inputLen) throws IllegalStateException {
        if (!initialized) {
            throw new IllegalStateException(
                "ExemptionMechanism not initialized");
        }
        if (inputLen < 0) {
            throw new IllegalArgumentException(
                "Input size must be equal to " + "or greater than zero");
        }
        return exmechSpi.engineGetOutputSize(inputLen);
    }

    
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.

Params:
  • key – the key for this exemption mechanism
Throws:
/**
     * Initializes this exemption mechanism with a key.
     *
     * <p>If this exemption mechanism requires any algorithm parameters
     * that cannot be derived from the given <code>key</code>, 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 <code>InvalidKeyException</code> is raised.
     *
     * @param key the key for this exemption mechanism
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * this exemption mechanism.
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of initializing.
     */
    public final void init(Key key)
            throws InvalidKeyException, ExemptionMechanismException {
        done = false;
        initialized = false;

        keyStored = key;
        exmechSpi.engineInit(key);
        initialized = true;
    }

    
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.

Params:
  • key – the key for this exemption mechanism
  • params – the algorithm parameters
Throws:
/**
     * Initializes this exemption mechanism with a key and a set of algorithm
     * parameters.
     *
     * <p>If this exemption mechanism requires any algorithm parameters
     * and <code>params</code> 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
     * <code>InvalidAlgorithmParameterException</code> is raised.
     *
     * @param key the key for this exemption mechanism
     * @param params the algorithm parameters
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * this exemption mechanism.
     * @exception InvalidAlgorithmParameterException if the given algorithm
     * parameters are inappropriate for this exemption mechanism.
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of initializing.
     */
    public final void init(Key key, AlgorithmParameterSpec params)
            throws InvalidKeyException, InvalidAlgorithmParameterException,
            ExemptionMechanismException {
        done = false;
        initialized = false;

        keyStored = key;
        exmechSpi.engineInit(key, params);
        initialized = true;
    }

    
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.

Params:
  • key – the key for this exemption mechanism
  • params – the algorithm parameters
Throws:
/**
     * Initializes this exemption mechanism with a key and a set of algorithm
     * parameters.
     *
     * <p>If this exemption mechanism requires any algorithm parameters
     * and <code>params</code> 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
     * <code>InvalidAlgorithmParameterException</code> is raised.
     *
     * @param key the key for this exemption mechanism
     * @param params the algorithm parameters
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * this exemption mechanism.
     * @exception InvalidAlgorithmParameterException if the given algorithm
     * parameters are inappropriate for this exemption mechanism.
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of initializing.
     */
    public final void init(Key key, AlgorithmParameters params)
            throws InvalidKeyException, InvalidAlgorithmParameterException,
            ExemptionMechanismException {
        done = false;
        initialized = false;

        keyStored = key;
        exmechSpi.engineInit(key, params);
        initialized = true;
    }

    
Generates the exemption mechanism key blob.

Throws:
Returns:the new buffer with the result key blob.
/**
     * Generates the exemption mechanism key blob.
     *
     * @return the new buffer with the result key blob.
     *
     * @exception IllegalStateException if this exemption mechanism is in
     * a wrong state (e.g., has not been initialized).
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of generating.
     */
    public final byte[] genExemptionBlob() throws IllegalStateException,
            ExemptionMechanismException {
        if (!initialized) {
            throw new IllegalStateException(
                "ExemptionMechanism not initialized");
        }
        byte[] blob = exmechSpi.engineGenExemptionBlob();
        done = true;
        return blob;
    }

    
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. 
Params:
  • output – the buffer for the result
Throws:
Returns:the number of bytes stored in output
/**
     * Generates the exemption mechanism key blob, and stores the result in
     * the <code>output</code> buffer.
     *
     * <p>If the <code>output</code> buffer is too small to hold the result,
     * a <code>ShortBufferException</code> is thrown. In this case, repeat this
     * call with a larger output buffer. Use
     * {@link #getOutputSize(int) getOutputSize} to determine how big
     * the output buffer should be.
     *
     * @param output the buffer for the result
     *
     * @return the number of bytes stored in <code>output</code>
     *
     * @exception IllegalStateException if this exemption mechanism is in
     * a wrong state (e.g., has not been initialized).
     * @exception ShortBufferException if the given output buffer is too small
     * to hold the result.
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of generating.
     */
    public final int genExemptionBlob(byte[] output)
            throws IllegalStateException, ShortBufferException,
            ExemptionMechanismException {
        if (!initialized) {
            throw new IllegalStateException
            ("ExemptionMechanism not initialized");
        }
        int n = exmechSpi.engineGenExemptionBlob(output, 0);
        done = true;
        return n;
    }

    
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. 
Params:
  • output – the buffer for the result
  • outputOffset – the offset in output where the result
is stored
Throws:
Returns:the number of bytes stored in output
/**
     * Generates the exemption mechanism key blob, and stores the result in
     * the <code>output</code> buffer, starting at <code>outputOffset</code>
     * inclusive.
     *
     * <p>If the <code>output</code> buffer is too small to hold the result,
     * a <code>ShortBufferException</code> is thrown. In this case, repeat this
     * call with a larger output buffer. Use
     * {@link #getOutputSize(int) getOutputSize} to determine how big
     * the output buffer should be.
     *
     * @param output the buffer for the result
     * @param outputOffset the offset in <code>output</code> where the result
     * is stored
     *
     * @return the number of bytes stored in <code>output</code>
     *
     * @exception IllegalStateException if this exemption mechanism is in
     * a wrong state (e.g., has not been initialized).
     * @exception ShortBufferException if the given output buffer is too small
     * to hold the result.
     * @exception ExemptionMechanismException if problem(s) encountered in the
     * process of generating.
     */
    public final int genExemptionBlob(byte[] output, int outputOffset)
            throws IllegalStateException, ShortBufferException,
            ExemptionMechanismException {
        if (!initialized) {
            throw new IllegalStateException
            ("ExemptionMechanism not initialized");
        }
        int n = exmechSpi.engineGenExemptionBlob(output, outputOffset);
        done = true;
        return n;
    }

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

/**
     * Ensures that the key stored away by this ExemptionMechanism
     * object will be wiped out when there are no more references to it.
     */
    protected void finalize() {
        keyStored = null;
        // Are there anything else we could do?
    }
}