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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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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
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package java.security;

import java.util.*;
import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.nio.ByteBuffer;

import sun.security.util.Debug;
import sun.security.util.MessageDigestSpi2;

import javax.crypto.SecretKey;

This MessageDigest class provides applications the functionality of a
message digest algorithm, such as SHA-1 or SHA-256.
Message digests are secure one-way hash functions that take arbitrary-sized
data and output a fixed-length hash value.
A MessageDigest object starts out initialized. The data is processed through it using the update methods. At any point reset can be called to reset the digest. Once all the data to be updated has been updated, one of the digest methods should be called to complete the hash computation. 
The digest method can be called once for a given number of updates. After digest has been called, the MessageDigest object is reset to its initialized state. 
Implementations are free to implement the Cloneable interface.
Client applications can test cloneability by attempting cloning
and catching the CloneNotSupportedException:

MessageDigest md = MessageDigest.getInstance("SHA-256");
try {
    md.update(toChapter1);
    MessageDigest tc1 = md.clone();
    byte[] toChapter1Digest = tc1.digest();
    md.update(toChapter2);
    ...etc.
 } catch (CloneNotSupportedException cnse) {
    throw new DigestException("couldn't make digest of partial content");
 }

Note that if a given implementation is not cloneable, it is
still possible to compute intermediate digests by instantiating
several instances, if the number of digests is known in advance.
Note that this class is abstract and extends from MessageDigestSpi for historical reasons. Application developers should only take notice of the methods defined in this MessageDigest class; all the methods in the superclass are intended for cryptographic service providers who wish to supply their own implementations of message digest algorithms. 
 Every implementation of the Java platform is required to support the following standard MessageDigest algorithms: 

MD5
SHA-1
SHA-256

These algorithms are described in the 
MessageDigest section of the
Java Security Standard Algorithm Names Specification.
Consult the release documentation for your implementation to see if any
other algorithms are supported.
Author:
Benjamin Renaud
See Also:
DigestInputStream
DigestOutputStream
Since:
1.1/**
 * This MessageDigest class provides applications the functionality of a
 * message digest algorithm, such as SHA-1 or SHA-256.
 * Message digests are secure one-way hash functions that take arbitrary-sized
 * data and output a fixed-length hash value.
 *
 * <p>A MessageDigest object starts out initialized. The data is
 * processed through it using the {@link #update(byte) update}
 * methods. At any point {@link #reset() reset} can be called
 * to reset the digest. Once all the data to be updated has been
 * updated, one of the {@link #digest() digest} methods should
 * be called to complete the hash computation.
 *
 * <p>The {@code digest} method can be called once for a given number
 * of updates. After {@code digest} has been called, the MessageDigest
 * object is reset to its initialized state.
 *
 * <p>Implementations are free to implement the Cloneable interface.
 * Client applications can test cloneability by attempting cloning
 * and catching the CloneNotSupportedException:
 *
 * <pre>{@code
 * MessageDigest md = MessageDigest.getInstance("SHA-256");
 *
 * try {
 *     md.update(toChapter1);
 *     MessageDigest tc1 = md.clone();
 *     byte[] toChapter1Digest = tc1.digest();
 *     md.update(toChapter2);
 *     ...etc.
 * } catch (CloneNotSupportedException cnse) {
 *     throw new DigestException("couldn't make digest of partial content");
 * }
 * }</pre>
 *
 * <p>Note that if a given implementation is not cloneable, it is
 * still possible to compute intermediate digests by instantiating
 * several instances, if the number of digests is known in advance.
 *
 * <p>Note that this class is abstract and extends from
 * {@code MessageDigestSpi} for historical reasons.
 * Application developers should only take notice of the methods defined in
 * this {@code MessageDigest} class; all the methods in
 * the superclass are intended for cryptographic service providers who wish to
 * supply their own implementations of message digest algorithms.
 *
 * <p> Every implementation of the Java platform is required to support
 * the following standard {@code MessageDigest} algorithms:
 * <ul>
 * <li>{@code MD5}</li>
 * <li>{@code SHA-1}</li>
 * <li>{@code SHA-256}</li>
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
 * MessageDigest section</a> of the
 * Java Security Standard Algorithm Names Specification.
 * Consult the release documentation for your implementation to see if any
 * other algorithms are supported.
 *
 * @author Benjamin Renaud
 * @since 1.1
 *
 * @see DigestInputStream
 * @see DigestOutputStream
 */

public abstract class MessageDigest extends MessageDigestSpi {

    private static final Debug pdebug =
                        Debug.getInstance("provider", "Provider");
    private static final boolean skipDebug =
        Debug.isOn("engine=") && !Debug.isOn("messagedigest");

    private String algorithm;

    // The state of this digest
    private static final int INITIAL = 0;
    private static final int IN_PROGRESS = 1;
    private int state = INITIAL;

    // The provider
    private Provider provider;

    
Creates a message digest with the specified algorithm name.
Params:
algorithm – the standard name of the digest algorithm.
See the MessageDigest section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names./**
     * Creates a message digest with the specified algorithm name.
     *
     * @param algorithm the standard name of the digest algorithm.
     * See the MessageDigest section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     */
    protected MessageDigest(String algorithm) {
        this.algorithm = algorithm;
    }

    
Returns a MessageDigest object that implements the specified digest
algorithm.
 This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new MessageDigest object encapsulating the
MessageDigestSpi 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 name of the algorithm requested.
See the MessageDigest section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
Throws:
NoSuchAlgorithmException – if no Provider supports a MessageDigestSpi implementation for the specified algorithm
NullPointerException – if algorithm is null
See Also:
Provider
Implementation Note:
 The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Returns:
a MessageDigest object that implements the specified algorithm/**
     * Returns a MessageDigest object that implements the specified digest
     * algorithm.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new MessageDigest object encapsulating the
     * MessageDigestSpi 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.
     *
     * @implNote
     * The JDK Reference Implementation additionally uses the
     * {@code jdk.security.provider.preferred}
     * {@link Security#getProperty(String) Security} property to determine
     * the preferred provider order for the specified algorithm. This
     * may be different than the order of providers returned by
     * {@link Security#getProviders() Security.getProviders()}.
     *
     * @param algorithm the name of the algorithm requested.
     * See the MessageDigest section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @return a {@code MessageDigest} object that implements the
     *         specified algorithm
     *
     * @throws NoSuchAlgorithmException if no {@code Provider} supports a
     *         {@code MessageDigestSpi} implementation for the
     *         specified algorithm
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     */
    public static MessageDigest getInstance(String algorithm)
    throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        try {
            MessageDigest md;
            Object[] objs = Security.getImpl(algorithm, "MessageDigest",
                                             (String)null);
            if (objs[0] instanceof MessageDigest) {
                md = (MessageDigest)objs[0];
            } else {
                md = new Delegate((MessageDigestSpi)objs[0], algorithm);
            }
            md.provider = (Provider)objs[1];

            if (!skipDebug && pdebug != null) {
                pdebug.println("MessageDigest." + algorithm +
                    " algorithm from: " + md.provider.getName());
            }

            return md;

        } catch(NoSuchProviderException e) {
            throw new NoSuchAlgorithmException(algorithm + " not found");
        }
    }

    
Returns a MessageDigest object that implements the specified digest
algorithm.
 A new MessageDigest object encapsulating the
MessageDigestSpi 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 name of the algorithm requested.
See the MessageDigest section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
provider – the name of the provider.
Throws:
IllegalArgumentException – if the provider name is null or empty
NoSuchAlgorithmException – if a MessageDigestSpi 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
NullPointerException – if algorithm is null
See Also:
Provider
Returns:
a MessageDigest object that implements the specified algorithm/**
     * Returns a MessageDigest object that implements the specified digest
     * algorithm.
     *
     * <p> A new MessageDigest object encapsulating the
     * MessageDigestSpi 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 name of the algorithm requested.
     * See the MessageDigest section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return a {@code MessageDigest} object that implements the
     *         specified algorithm
     *
     * @throws IllegalArgumentException if the provider name is {@code null}
     *         or empty
     *
     * @throws NoSuchAlgorithmException if a {@code MessageDigestSpi}
     *         implementation for the specified algorithm is not
     *         available from the specified provider
     *
     * @throws NoSuchProviderException if the specified provider is not
     *         registered in the security provider list
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     */
    public static MessageDigest getInstance(String algorithm, String provider)
        throws NoSuchAlgorithmException, NoSuchProviderException
    {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (provider == null || provider.isEmpty())
            throw new IllegalArgumentException("missing provider");
        Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
        if (objs[0] instanceof MessageDigest) {
            MessageDigest md = (MessageDigest)objs[0];
            md.provider = (Provider)objs[1];
            return md;
        } else {
            MessageDigest delegate =
                new Delegate((MessageDigestSpi)objs[0], algorithm);
            delegate.provider = (Provider)objs[1];
            return delegate;
        }
    }

    
Returns a MessageDigest object that implements the specified digest
algorithm.
 A new MessageDigest object encapsulating the
MessageDigestSpi 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 name of the algorithm requested.
See the MessageDigest section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
provider – the provider.
Throws:
IllegalArgumentException – if the specified provider is null
NoSuchAlgorithmException – if a MessageDigestSpi implementation for the specified algorithm is not available from the specified Provider object
NullPointerException – if algorithm is null
See Also:
Provider
Returns:
a MessageDigest object that implements the specified algorithm
Since:
1.4/**
     * Returns a MessageDigest object that implements the specified digest
     * algorithm.
     *
     * <p> A new MessageDigest object encapsulating the
     * MessageDigestSpi 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 name of the algorithm requested.
     * See the MessageDigest section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return a {@code MessageDigest} object that implements the
     *         specified algorithm
     *
     * @throws IllegalArgumentException if the specified provider is
     *         {@code null}
     *
     * @throws NoSuchAlgorithmException if a {@code MessageDigestSpi}
     *         implementation for the specified algorithm is not available
     *         from the specified {@code Provider} object
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 1.4
     */
    public static MessageDigest getInstance(String algorithm,
                                            Provider provider)
        throws NoSuchAlgorithmException
    {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (provider == null)
            throw new IllegalArgumentException("missing provider");
        Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
        if (objs[0] instanceof MessageDigest) {
            MessageDigest md = (MessageDigest)objs[0];
            md.provider = (Provider)objs[1];
            return md;
        } else {
            MessageDigest delegate =
                new Delegate((MessageDigestSpi)objs[0], algorithm);
            delegate.provider = (Provider)objs[1];
            return delegate;
        }
    }

    
Returns the provider of this message digest object.
Returns:
the provider of this message digest object/**
     * Returns the provider of this message digest object.
     *
     * @return the provider of this message digest object
     */
    public final Provider getProvider() {
        return this.provider;
    }

    
Updates the digest using the specified byte.
Params:
input – the byte with which to update the digest./**
     * Updates the digest using the specified byte.
     *
     * @param input the byte with which to update the digest.
     */
    public void update(byte input) {
        engineUpdate(input);
        state = IN_PROGRESS;
    }

    
Updates the digest using the specified array of bytes, starting
at the specified offset.
Params:
input – the array of bytes.
offset – the offset to start from in the array of bytes.
len – the number of bytes to use, starting at offset./**
     * Updates the digest using the specified array of bytes, starting
     * at the specified offset.
     *
     * @param input the array of bytes.
     *
     * @param offset the offset to start from in the array of bytes.
     *
     * @param len the number of bytes to use, starting at
     * {@code offset}.
     */
    public void update(byte[] input, int offset, int len) {
        if (input == null) {
            throw new IllegalArgumentException("No input buffer given");
        }
        if (input.length - offset < len) {
            throw new IllegalArgumentException("Input buffer too short");
        }
        engineUpdate(input, offset, len);
        state = IN_PROGRESS;
    }

    
Updates the digest using the specified array of bytes.
Params:
input – the array of bytes./**
     * Updates the digest using the specified array of bytes.
     *
     * @param input the array of bytes.
     */
    public void update(byte[] input) {
        engineUpdate(input, 0, input.length);
        state = IN_PROGRESS;
    }

    
Update the digest using the specified ByteBuffer. The digest is updated using the input.remaining() bytes 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
Since:
1.5/**
     * Update the digest using the specified ByteBuffer. The digest is
     * updated using the {@code input.remaining()} bytes starting
     * at {@code input.position()}.
     * Upon return, the buffer's position will be equal to its limit;
     * its limit will not have changed.
     *
     * @param input the ByteBuffer
     * @since 1.5
     */
    public final void update(ByteBuffer input) {
        if (input == null) {
            throw new NullPointerException();
        }
        engineUpdate(input);
        state = IN_PROGRESS;
    }

    
Completes the hash computation by performing final operations
such as padding. The digest is reset after this call is made.
Returns:
the array of bytes for the resulting hash value./**
     * Completes the hash computation by performing final operations
     * such as padding. The digest is reset after this call is made.
     *
     * @return the array of bytes for the resulting hash value.
     */
    public byte[] digest() {
        /* Resetting is the responsibility of implementors. */
        byte[] result = engineDigest();
        state = INITIAL;
        return result;
    }

    
Completes the hash computation by performing final operations
such as padding. The digest is reset after this call is made.
Params:
buf – output buffer for the computed digest
offset – offset into the output buffer to begin storing the digest
len – number of bytes within buf allotted for the digest
Throws:
DigestException – if an error occurs.
Returns:
the number of bytes placed into buf/**
     * Completes the hash computation by performing final operations
     * such as padding. The digest is reset after this call is made.
     *
     * @param buf output buffer for the computed digest
     *
     * @param offset offset into the output buffer to begin storing the digest
     *
     * @param len number of bytes within buf allotted for the digest
     *
     * @return the number of bytes placed into {@code buf}
     *
     * @exception DigestException if an error occurs.
     */
    public int digest(byte[] buf, int offset, int len) throws DigestException {
        if (buf == null) {
            throw new IllegalArgumentException("No output buffer given");
        }
        if (buf.length - offset < len) {
            throw new IllegalArgumentException
                ("Output buffer too small for specified offset and length");
        }
        int numBytes = engineDigest(buf, offset, len);
        state = INITIAL;
        return numBytes;
    }

    
Performs a final update on the digest using the specified array of bytes, then completes the digest computation. That is, this method first calls update(input), passing the input array to the update method, then calls digest(). 
Params:
input – the input to be updated before the digest is
completed.
Returns:
the array of bytes for the resulting hash value./**
     * Performs a final update on the digest using the specified array
     * of bytes, then completes the digest computation. That is, this
     * method first calls {@link #update(byte[]) update(input)},
     * passing the <i>input</i> array to the {@code update} method,
     * then calls {@link #digest() digest()}.
     *
     * @param input the input to be updated before the digest is
     * completed.
     *
     * @return the array of bytes for the resulting hash value.
     */
    public byte[] digest(byte[] input) {
        update(input);
        return digest();
    }

    private String getProviderName() {
        return (provider == null) ? "(no provider)" : provider.getName();
    }

    
Returns a string representation of this message digest object.
/**
     * Returns a string representation of this message digest object.
     */
    public String toString() {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        PrintStream p = new PrintStream(baos);
        p.print(algorithm+" Message Digest from "+getProviderName()+", ");
        switch (state) {
        case INITIAL:
            p.print("<initialized>");
            break;
        case IN_PROGRESS:
            p.print("<in progress>");
            break;
        }
        p.println();
        return (baos.toString());
    }

    
Compares two digests for equality. Two digests are equal if they have
the same length and all bytes at corresponding positions are equal.
Params:
digesta – one of the digests to compare.
digestb – the other digest to compare.
Implementation Note:
 All bytes in digesta are examined to determine equality. The calculation time depends only on the length of digesta. It does not depend on the length of digestb or the contents of digesta and digestb.
Returns:
true if the digests are equal, false otherwise./**
     * Compares two digests for equality. Two digests are equal if they have
     * the same length and all bytes at corresponding positions are equal.
     *
     * @implNote
     * All bytes in {@code digesta} are examined to determine equality.
     * The calculation time depends only on the length of {@code digesta}.
     * It does not depend on the length of {@code digestb} or the contents
     * of {@code digesta} and {@code digestb}.
     *
     * @param digesta one of the digests to compare.
     *
     * @param digestb the other digest to compare.
     *
     * @return true if the digests are equal, false otherwise.
     */
    public static boolean isEqual(byte[] digesta, byte[] digestb) {
        if (digesta == digestb) return true;
        if (digesta == null || digestb == null) {
            return false;
        }

        int lenA = digesta.length;
        int lenB = digestb.length;

        if (lenB == 0) {
            return lenA == 0;
        }

        int result = 0;
        result |= lenA - lenB;

        // time-constant comparison
        for (int i = 0; i < lenA; i++) {
            // If i >= lenB, indexB is 0; otherwise, i.
            int indexB = ((i - lenB) >>> 31) * i;
            result |= digesta[i] ^ digestb[indexB];
        }
        return result == 0;
    }

    
Resets the digest for further use.
/**
     * Resets the digest for further use.
     */
    public void reset() {
        engineReset();
        state = INITIAL;
    }

    
Returns a string that identifies the algorithm, independent of
implementation details. The name should be a standard
Java Security name (such as "SHA-256").
See the MessageDigest section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
Returns:
the name of the algorithm/**
     * Returns a string that identifies the algorithm, independent of
     * implementation details. The name should be a standard
     * Java Security name (such as "SHA-256").
     * See the MessageDigest section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#messagedigest-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @return the name of the algorithm
     */
    public final String getAlgorithm() {
        return this.algorithm;
    }

    
Returns the length of the digest in bytes, or 0 if this operation is
not supported by the provider and the implementation is not cloneable.
Returns:
the digest length in bytes, or 0 if this operation is not
supported by the provider and the implementation is not cloneable.
Since:
1.2/**
     * Returns the length of the digest in bytes, or 0 if this operation is
     * not supported by the provider and the implementation is not cloneable.
     *
     * @return the digest length in bytes, or 0 if this operation is not
     * supported by the provider and the implementation is not cloneable.
     *
     * @since 1.2
     */
    public final int getDigestLength() {
        int digestLen = engineGetDigestLength();
        if (digestLen == 0) {
            try {
                MessageDigest md = (MessageDigest)clone();
                byte[] digest = md.digest();
                return digest.length;
            } catch (CloneNotSupportedException e) {
                return digestLen;
            }
        }
        return digestLen;
    }

    
Returns a clone if the implementation is cloneable.
Throws:
CloneNotSupportedException – if this is called on an implementation that does not support Cloneable.
Returns:
a clone if the implementation is cloneable./**
     * Returns a clone if the implementation is cloneable.
     *
     * @return a clone if the implementation is cloneable.
     *
     * @exception CloneNotSupportedException if this is called on an
     * implementation that does not support {@code Cloneable}.
     */
    public Object clone() throws CloneNotSupportedException {
        if (this instanceof Cloneable) {
            return super.clone();
        } else {
            throw new CloneNotSupportedException();
        }
    }




    /*
     * The following class allows providers to extend from MessageDigestSpi
     * rather than from MessageDigest. It represents a MessageDigest with an
     * encapsulated, provider-supplied SPI object (of type MessageDigestSpi).
     * If the provider implementation is an instance of MessageDigestSpi,
     * the getInstance() methods above return an instance of this class, with
     * the SPI object encapsulated.
     *
     * Note: All SPI methods from the original MessageDigest class have been
     * moved up the hierarchy into a new class (MessageDigestSpi), which has
     * been interposed in the hierarchy between the API (MessageDigest)
     * and its original parent (Object).
     */

    static class Delegate extends MessageDigest implements MessageDigestSpi2 {

        // The provider implementation (delegate)
        private MessageDigestSpi digestSpi;

        // constructor
        public Delegate(MessageDigestSpi digestSpi, String algorithm) {
            super(algorithm);
            this.digestSpi = digestSpi;
        }

        
Returns a clone if the delegate is cloneable.
Throws:
CloneNotSupportedException – if this is called on a delegate that does not support Cloneable.
Returns:
a clone if the delegate is cloneable./**
         * Returns a clone if the delegate is cloneable.
         *
         * @return a clone if the delegate is cloneable.
         *
         * @exception CloneNotSupportedException if this is called on a
         * delegate that does not support {@code Cloneable}.
         */
        public Object clone() throws CloneNotSupportedException {
            if (digestSpi instanceof Cloneable) {
                MessageDigestSpi digestSpiClone =
                    (MessageDigestSpi)digestSpi.clone();
                // Because 'algorithm', 'provider', and 'state' are private
                // members of our supertype, we must perform a cast to
                // access them.
                MessageDigest that =
                    new Delegate(digestSpiClone,
                                 ((MessageDigest)this).algorithm);
                that.provider = ((MessageDigest)this).provider;
                that.state = ((MessageDigest)this).state;
                return that;
            } else {
                throw new CloneNotSupportedException();
            }
        }

        protected int engineGetDigestLength() {
            return digestSpi.engineGetDigestLength();
        }

        protected void engineUpdate(byte input) {
            digestSpi.engineUpdate(input);
        }

        protected void engineUpdate(byte[] input, int offset, int len) {
            digestSpi.engineUpdate(input, offset, len);
        }

        protected void engineUpdate(ByteBuffer input) {
            digestSpi.engineUpdate(input);
        }

        public void engineUpdate(SecretKey key) throws InvalidKeyException {
            if (digestSpi instanceof MessageDigestSpi2) {
                ((MessageDigestSpi2)digestSpi).engineUpdate(key);
            } else {
                throw new UnsupportedOperationException
                ("Digest does not support update of SecretKey object");
            }
        }
        protected byte[] engineDigest() {
            return digestSpi.engineDigest();
        }

        protected int engineDigest(byte[] buf, int offset, int len)
            throws DigestException {
                return digestSpi.engineDigest(buf, offset, len);
        }

        protected void engineReset() {
            digestSpi.engineReset();
        }
    }
}