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 * Copyright (c) 1998, 2017, 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
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package javax.crypto;

import java.util.*;

import java.security.*;
import java.security.Provider.Service;
import java.security.spec.AlgorithmParameterSpec;

import java.nio.ByteBuffer;

import sun.security.util.Debug;
import sun.security.jca.*;
import sun.security.jca.GetInstance.Instance;

This class provides the functionality of a "Message Authentication Code"
(MAC) algorithm.
 A MAC provides a way to check
the integrity of information transmitted over or stored in an unreliable
medium, based on a secret key. Typically, message
authentication codes are used between two parties that share a secret
key in order to validate information transmitted between these
parties.
 A MAC mechanism that is based on cryptographic hash functions is
referred to as HMAC. HMAC can be used with any cryptographic hash function,
e.g., SHA256 or SHA384, in combination with a secret shared key. HMAC is
specified in RFC 2104.
Author:
Jan Luehe
Since:
1.4/**
 * This class provides the functionality of a "Message Authentication Code"
 * (MAC) algorithm.
 *
 * <p> A MAC provides a way to check
 * the integrity of information transmitted over or stored in an unreliable
 * medium, based on a secret key. Typically, message
 * authentication codes are used between two parties that share a secret
 * key in order to validate information transmitted between these
 * parties.
 *
 * <p> A MAC mechanism that is based on cryptographic hash functions is
 * referred to as HMAC. HMAC can be used with any cryptographic hash function,
 * e.g., SHA256 or SHA384, in combination with a secret shared key. HMAC is
 * specified in RFC 2104.
 *
 * @author Jan Luehe
 *
 * @since 1.4
 */

public class Mac implements Cloneable {

    private static final Debug debug =
                        Debug.getInstance("jca", "Mac");

    // The provider
    private Provider provider;

    // The provider implementation (delegate)
    private MacSpi spi;

    // The name of the MAC algorithm.
    private final String algorithm;

    // Has this object been initialized?
    private boolean initialized = false;

    // next service to try in provider selection
    // null once provider is selected
    private Service firstService;

    // remaining services to try in provider selection
    // null once provider is selected
    private Iterator<Service> serviceIterator;

    private final Object lock;

    
Creates a MAC object.
Params:
macSpi – the delegate
provider – the provider
algorithm – the algorithm/**
     * Creates a MAC object.
     *
     * @param macSpi the delegate
     * @param provider the provider
     * @param algorithm the algorithm
     */
    protected Mac(MacSpi macSpi, Provider provider, String algorithm) {
        this.spi = macSpi;
        this.provider = provider;
        this.algorithm = algorithm;
        serviceIterator = null;
        lock = null;
    }

    private Mac(Service s, Iterator<Service> t, String algorithm) {
        firstService = s;
        serviceIterator = t;
        this.algorithm = algorithm;
        lock = new Object();
    }

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

    
Returns a Mac object that implements the
specified MAC algorithm.
 This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new Mac object encapsulating the
MacSpi 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:
algorithm – the standard name of the requested MAC algorithm.
See Appendix A in the 
Java Cryptography Architecture Reference Guide
for information about standard algorithm names.
Throws:
NoSuchAlgorithmException – if no Provider supports a
         MacSpi implementation for the
         specified algorithm.
See Also:
Provider
Returns:
the new Mac object./**
     * Returns a <code>Mac</code> object that implements the
     * specified MAC algorithm.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new Mac object encapsulating the
     * MacSpi 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 MAC algorithm.
     * See Appendix A in the <a href=
     *   "{@docRoot}/../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture Reference Guide</a>
     * for information about standard algorithm names.
     *
     * @return the new <code>Mac</code> object.
     *
     * @exception NoSuchAlgorithmException if no Provider supports a
     *          MacSpi implementation for the
     *          specified algorithm.
     *
     * @see java.security.Provider
     */
    public static final Mac getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        List<Service> services = GetInstance.getServices("Mac", algorithm);
        // make sure there is at least one service from a signed provider
        Iterator<Service> t = services.iterator();
        while (t.hasNext()) {
            Service s = t.next();
            if (JceSecurity.canUseProvider(s.getProvider()) == false) {
                continue;
            }
            return new Mac(s, t, algorithm);
        }
        throw new NoSuchAlgorithmException
                                ("Algorithm " + algorithm + " not available");
    }

    
Returns a Mac object that implements the
specified MAC algorithm.
 A new Mac object encapsulating the
MacSpi 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:
algorithm – the standard name of the requested MAC algorithm.
See Appendix A in the 
Java Cryptography Architecture Reference Guide
for information about standard algorithm names.
provider – the name of the provider.
Throws:
NoSuchAlgorithmException – if a MacSpi
         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
Returns:
the new Mac object./**
     * Returns a <code>Mac</code> object that implements the
     * specified MAC algorithm.
     *
     * <p> A new Mac object encapsulating the
     * MacSpi 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 MAC algorithm.
     * See Appendix A in the <a href=
     *   "{@docRoot}/../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture Reference Guide</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new <code>Mac</code> object.
     *
     * @exception NoSuchAlgorithmException if a MacSpi
     *          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 Mac getInstance(String algorithm, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        Instance instance = JceSecurity.getInstance
                ("Mac", MacSpi.class, algorithm, provider);
        return new Mac((MacSpi)instance.impl, instance.provider, algorithm);
    }

    
Returns a Mac object that implements the
specified MAC algorithm.
 A new Mac object encapsulating the
MacSpi 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:
algorithm – the standard name of the requested MAC algorithm.
See Appendix A in the 
Java Cryptography Architecture Reference Guide
for information about standard algorithm names.
provider – the provider.
Throws:
NoSuchAlgorithmException – if a MacSpi
         implementation for the specified algorithm is not available
         from the specified Provider object.
IllegalArgumentException – if the provider
         is null.
See Also:
Provider
Returns:
the new Mac object./**
     * Returns a <code>Mac</code> object that implements the
     * specified MAC algorithm.
     *
     * <p> A new Mac object encapsulating the
     * MacSpi 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 MAC algorithm.
     * See Appendix A in the <a href=
     *   "{@docRoot}/../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture Reference Guide</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new <code>Mac</code> object.
     *
     * @exception NoSuchAlgorithmException if a MacSpi
     *          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 Mac getInstance(String algorithm, Provider provider)
            throws NoSuchAlgorithmException {
        Instance instance = JceSecurity.getInstance
                ("Mac", MacSpi.class, algorithm, provider);
        return new Mac((MacSpi)instance.impl, instance.provider, algorithm);
    }

    // max number of debug warnings to print from chooseFirstProvider()
    private static int warnCount = 10;

    
Choose the Spi from the first provider available. Used if
delayed provider selection is not possible because init()
is not the first method called.
/**
     * Choose the Spi from the first provider available. Used if
     * delayed provider selection is not possible because init()
     * is not the first method called.
     */
    void chooseFirstProvider() {
        if ((spi != null) || (serviceIterator == null)) {
            return;
        }
        synchronized (lock) {
            if (spi != null) {
                return;
            }
            if (debug != null) {
                int w = --warnCount;
                if (w >= 0) {
                    debug.println("Mac.init() not first method "
                        + "called, disabling delayed provider selection");
                    if (w == 0) {
                        debug.println("Further warnings of this type will "
                            + "be suppressed");
                    }
                    new Exception("Call trace").printStackTrace();
                }
            }
            Exception lastException = null;
            while ((firstService != null) || serviceIterator.hasNext()) {
                Service s;
                if (firstService != null) {
                    s = firstService;
                    firstService = null;
                } else {
                    s = serviceIterator.next();
                }
                if (JceSecurity.canUseProvider(s.getProvider()) == false) {
                    continue;
                }
                try {
                    Object obj = s.newInstance(null);
                    if (obj instanceof MacSpi == false) {
                        continue;
                    }
                    spi = (MacSpi)obj;
                    provider = s.getProvider();
                    // not needed any more
                    firstService = null;
                    serviceIterator = null;
                    return;
                } catch (NoSuchAlgorithmException e) {
                    lastException = e;
                }
            }
            ProviderException e = new ProviderException
                    ("Could not construct MacSpi instance");
            if (lastException != null) {
                e.initCause(lastException);
            }
            throw e;
        }
    }

    private void chooseProvider(Key key, AlgorithmParameterSpec params)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        synchronized (lock) {
            if (spi != null) {
                spi.engineInit(key, params);
                return;
            }
            Exception lastException = null;
            while ((firstService != null) || serviceIterator.hasNext()) {
                Service s;
                if (firstService != null) {
                    s = firstService;
                    firstService = null;
                } else {
                    s = serviceIterator.next();
                }
                // if provider says it does not support this key, ignore it
                if (s.supportsParameter(key) == false) {
                    continue;
                }
                if (JceSecurity.canUseProvider(s.getProvider()) == false) {
                    continue;
                }
                try {
                    MacSpi spi = (MacSpi)s.newInstance(null);
                    spi.engineInit(key, params);
                    provider = s.getProvider();
                    this.spi = spi;
                    firstService = null;
                    serviceIterator = null;
                    return;
                } catch (Exception e) {
                    // NoSuchAlgorithmException from newInstance()
                    // InvalidKeyException from init()
                    // RuntimeException (ProviderException) from init()
                    if (lastException == null) {
                        lastException = e;
                    }
                }
            }
            // no working provider found, fail
            if (lastException instanceof InvalidKeyException) {
                throw (InvalidKeyException)lastException;
            }
            if (lastException instanceof InvalidAlgorithmParameterException) {
                throw (InvalidAlgorithmParameterException)lastException;
            }
            if (lastException instanceof RuntimeException) {
                throw (RuntimeException)lastException;
            }
            String kName = (key != null) ? key.getClass().getName() : "(null)";
            throw new InvalidKeyException
                ("No installed provider supports this key: "
                + kName, lastException);
        }
    }

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

    
Returns the length of the MAC in bytes.
Returns:
the MAC length in bytes./**
     * Returns the length of the MAC in bytes.
     *
     * @return the MAC length in bytes.
     */
    public final int getMacLength() {
        chooseFirstProvider();
        return spi.engineGetMacLength();
    }

    
Initializes this Mac object with the given key.
Params:
key – the key.
Throws:
InvalidKeyException – if the given key is inappropriate for
initializing this MAC./**
     * Initializes this <code>Mac</code> object with the given key.
     *
     * @param key the key.
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * initializing this MAC.
     */
    public final void init(Key key) throws InvalidKeyException {
        try {
            if (spi != null) {
                spi.engineInit(key, null);
            } else {
                chooseProvider(key, null);
            }
        } catch (InvalidAlgorithmParameterException e) {
            throw new InvalidKeyException("init() failed", e);
        }
        initialized = true;
    }

    
Initializes this Mac object with the given key and
algorithm parameters.
Params:
key – the key.
params – the algorithm parameters.
Throws:
InvalidKeyException – if the given key is inappropriate for
initializing this MAC.
InvalidAlgorithmParameterException – if the given algorithm
parameters are inappropriate for this MAC./**
     * Initializes this <code>Mac</code> object with the given key and
     * algorithm parameters.
     *
     * @param key the key.
     * @param params the algorithm parameters.
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * initializing this MAC.
     * @exception InvalidAlgorithmParameterException if the given algorithm
     * parameters are inappropriate for this MAC.
     */
    public final void init(Key key, AlgorithmParameterSpec params)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        if (spi != null) {
            spi.engineInit(key, params);
        } else {
            chooseProvider(key, params);
        }
        initialized = true;
    }

    
Processes the given byte.
Params:
input – the input byte to be processed.
Throws:
IllegalStateException – if this Mac has not been
initialized./**
     * Processes the given byte.
     *
     * @param input the input byte to be processed.
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final void update(byte input) throws IllegalStateException {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        spi.engineUpdate(input);
    }

    
Processes the given array of bytes.
Params:
input – the array of bytes to be processed.
Throws:
IllegalStateException – if this Mac has not been
initialized./**
     * Processes the given array of bytes.
     *
     * @param input the array of bytes to be processed.
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final void update(byte[] input) throws IllegalStateException {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        if (input != null) {
            spi.engineUpdate(input, 0, input.length);
        }
    }

    
Processes the first len bytes in input,
starting at offset inclusive.
Params:
input – the input buffer.
offset – the offset in input where the input starts.
len – the number of bytes to process.
Throws:
IllegalStateException – if this Mac has not been
initialized./**
     * Processes the first <code>len</code> bytes in <code>input</code>,
     * starting at <code>offset</code> inclusive.
     *
     * @param input the input buffer.
     * @param offset the offset in <code>input</code> where the input starts.
     * @param len the number of bytes to process.
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final void update(byte[] input, int offset, int len)
            throws IllegalStateException {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }

        if (input != null) {
            if ((offset < 0) || (len > (input.length - offset)) || (len < 0))
                throw new IllegalArgumentException("Bad arguments");
            spi.engineUpdate(input, offset, len);
        }
    }

    
Processes input.remaining() bytes in the ByteBuffer
input, starting at input.position().
Upon return, the buffer's position will be equal to its limit;
its limit will not have changed.
Params:
input – the ByteBuffer
Throws:
IllegalStateException – if this Mac has not been
initialized.
Since:
1.5/**
     * Processes <code>input.remaining()</code> bytes in the ByteBuffer
     * <code>input</code>, starting at <code>input.position()</code>.
     * Upon return, the buffer's position will be equal to its limit;
     * its limit will not have changed.
     *
     * @param input the ByteBuffer
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     * @since 1.5
     */
    public final void update(ByteBuffer input) {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        if (input == null) {
            throw new IllegalArgumentException("Buffer must not be null");
        }
        spi.engineUpdate(input);
    }

    
Finishes the MAC operation.
A call to this method resets this Mac object to the
state it was in when previously initialized via a call to
init(Key) or
init(Key, AlgorithmParameterSpec).
That is, the object is reset and available to generate another MAC from
the same key, if desired, via new calls to update and
doFinal.
(In order to reuse this Mac object with a different key,
it must be reinitialized via a call to init(Key) or
init(Key, AlgorithmParameterSpec).
Throws:
IllegalStateException – if this Mac has not been
initialized.
Returns:
the MAC result./**
     * Finishes the MAC operation.
     *
     * <p>A call to this method resets this <code>Mac</code> object to the
     * state it was in when previously initialized via a call to
     * <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     * That is, the object is reset and available to generate another MAC from
     * the same key, if desired, via new calls to <code>update</code> and
     * <code>doFinal</code>.
     * (In order to reuse this <code>Mac</code> object with a different key,
     * it must be reinitialized via a call to <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     *
     * @return the MAC result.
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final byte[] doFinal() throws IllegalStateException {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        byte[] mac = spi.engineDoFinal();
        spi.engineReset();
        return mac;
    }

    
Finishes the MAC operation.
A call to this method resets this Mac object to the
state it was in when previously initialized via a call to
init(Key) or
init(Key, AlgorithmParameterSpec).
That is, the object is reset and available to generate another MAC from
the same key, if desired, via new calls to update and
doFinal.
(In order to reuse this Mac object with a different key,
it must be reinitialized via a call to init(Key) or
init(Key, AlgorithmParameterSpec).
The MAC result is stored in output, starting at
outOffset inclusive.
Params:
output – the buffer where the MAC result is stored
outOffset – the offset in output where the MAC is
stored
Throws:
ShortBufferException – if the given output buffer is too small
to hold the result
IllegalStateException – if this Mac has not been
initialized./**
     * Finishes the MAC operation.
     *
     * <p>A call to this method resets this <code>Mac</code> object to the
     * state it was in when previously initialized via a call to
     * <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     * That is, the object is reset and available to generate another MAC from
     * the same key, if desired, via new calls to <code>update</code> and
     * <code>doFinal</code>.
     * (In order to reuse this <code>Mac</code> object with a different key,
     * it must be reinitialized via a call to <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     *
     * <p>The MAC result is stored in <code>output</code>, starting at
     * <code>outOffset</code> inclusive.
     *
     * @param output the buffer where the MAC result is stored
     * @param outOffset the offset in <code>output</code> where the MAC is
     * stored
     *
     * @exception ShortBufferException if the given output buffer is too small
     * to hold the result
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final void doFinal(byte[] output, int outOffset)
        throws ShortBufferException, IllegalStateException
    {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        int macLen = getMacLength();
        if (output == null || output.length-outOffset < macLen) {
            throw new ShortBufferException
                ("Cannot store MAC in output buffer");
        }
        byte[] mac = doFinal();
        System.arraycopy(mac, 0, output, outOffset, macLen);
        return;
    }

    
Processes the given array of bytes and finishes the MAC operation.
A call to this method resets this Mac object to the
state it was in when previously initialized via a call to
init(Key) or
init(Key, AlgorithmParameterSpec).
That is, the object is reset and available to generate another MAC from
the same key, if desired, via new calls to update and
doFinal.
(In order to reuse this Mac object with a different key,
it must be reinitialized via a call to init(Key) or
init(Key, AlgorithmParameterSpec).
Params:
input – data in bytes
Throws:
IllegalStateException – if this Mac has not been
initialized.
Returns:
the MAC result./**
     * Processes the given array of bytes and finishes the MAC operation.
     *
     * <p>A call to this method resets this <code>Mac</code> object to the
     * state it was in when previously initialized via a call to
     * <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     * That is, the object is reset and available to generate another MAC from
     * the same key, if desired, via new calls to <code>update</code> and
     * <code>doFinal</code>.
     * (In order to reuse this <code>Mac</code> object with a different key,
     * it must be reinitialized via a call to <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     *
     * @param input data in bytes
     * @return the MAC result.
     *
     * @exception IllegalStateException if this <code>Mac</code> has not been
     * initialized.
     */
    public final byte[] doFinal(byte[] input) throws IllegalStateException
    {
        chooseFirstProvider();
        if (initialized == false) {
            throw new IllegalStateException("MAC not initialized");
        }
        update(input);
        return doFinal();
    }

    
Resets this Mac object.
A call to this method resets this Mac object to the
state it was in when previously initialized via a call to
init(Key) or
init(Key, AlgorithmParameterSpec).
That is, the object is reset and available to generate another MAC from
the same key, if desired, via new calls to update and
doFinal.
(In order to reuse this Mac object with a different key,
it must be reinitialized via a call to init(Key) or
init(Key, AlgorithmParameterSpec).
/**
     * Resets this <code>Mac</code> object.
     *
     * <p>A call to this method resets this <code>Mac</code> object to the
     * state it was in when previously initialized via a call to
     * <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     * That is, the object is reset and available to generate another MAC from
     * the same key, if desired, via new calls to <code>update</code> and
     * <code>doFinal</code>.
     * (In order to reuse this <code>Mac</code> object with a different key,
     * it must be reinitialized via a call to <code>init(Key)</code> or
     * <code>init(Key, AlgorithmParameterSpec)</code>.
     */
    public final void reset() {
        chooseFirstProvider();
        spi.engineReset();
    }

    
Returns a clone if the provider implementation is cloneable.
Throws:
CloneNotSupportedException – if this is called on a
delegate that does not support Cloneable.
Returns:
a clone if the provider implementation is cloneable./**
     * Returns a clone if the provider implementation is cloneable.
     *
     * @return a clone if the provider implementation is cloneable.
     *
     * @exception CloneNotSupportedException if this is called on a
     * delegate that does not support <code>Cloneable</code>.
     */
    public final Object clone() throws CloneNotSupportedException {
        chooseFirstProvider();
        Mac that = (Mac)super.clone();
        that.spi = (MacSpi)this.spi.clone();
        return that;
    }
}