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 * 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.security;

import java.util.*;

import java.lang.*;

import java.io.IOException;

import java.io.ByteArrayOutputStream;

import java.io.PrintStream;

import java.io.InputStream;

import java.io.ByteArrayInputStream;

import java.nio.ByteBuffer;

/**

 * 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");

 *

 * 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}/../technotes/guides/security/StandardNames.html#MessageDigest">

 * MessageDigest section</a> of the

 * Java Cryptography Architecture Standard Algorithm Name Documentation.

 * Consult the release documentation for your implementation to see if any

 * other algorithms are supported.

 *

 * @author Benjamin Renaud

 *

 * @see DigestInputStream

 * @see DigestOutputStream

 */

public abstract class MessageDigest extends MessageDigestSpi {

    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.

     *

     * @param algorithm the standard name of the digest algorithm.

     * See the MessageDigest section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     */

    protected MessageDigest(String algorithm) {

        this.algorithm = 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.

     *

     * @param algorithm the name of the algorithm requested.

     * See the MessageDigest section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     *

     * @return a Message Digest object that implements the specified algorithm.

     *

     * @exception NoSuchAlgorithmException if no Provider supports a

     *          MessageDigestSpi implementation for the

     *          specified algorithm.

     *

     * @see Provider

     */

    public static MessageDigest getInstance(String algorithm)

    throws NoSuchAlgorithmException {

        try {

            Object[] objs = Security.getImpl(algorithm, "MessageDigest",

                                             (String)null);

            if (objs[0] instanceof MessageDigest) {

            } else {

            }

        } catch(NoSuchProviderException e) {

            throw new NoSuchAlgorithmException(algorithm + " not found");

        }

    }

    /**

     * 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}/../technotes/guides/security/StandardNames.html#MessageDigest">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     *

     * @param provider the name of the provider.

     *

     * @return a MessageDigest object that implements the specified algorithm.

     *

     * @exception NoSuchAlgorithmException if a MessageDigestSpi

     *          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 provider name is null

     *          or empty.

     *

     * @see Provider

     */

    public static MessageDigest getInstance(String algorithm, String provider)

        throws NoSuchAlgorithmException, NoSuchProviderException

    {

        if (provider == null || provider.length() == 0)

            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.

     *

     * <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}/../technotes/guides/security/StandardNames.html#MessageDigest">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     *

     * @param provider the provider.

     *

     * @return a MessageDigest object that implements the specified algorithm.

     *

     * @exception NoSuchAlgorithmException if a MessageDigestSpi

     *          implementation for the specified algorithm is not available

     *          from the specified Provider object.

     *

     * @exception IllegalArgumentException if the specified provider is null.

     *

     * @see Provider

     *

     * @since 1.4

     */

    public static MessageDigest getInstance(String algorithm,

                                            Provider provider)

        throws NoSuchAlgorithmException

    {

        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.

     *

     * @return the provider of this message digest object

     */

    public final Provider getProvider() {

        return this.provider;

    }

    /**

     * 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.

     *

     * @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.

     *

     * @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 {@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.

     *

     * @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.

     *

     * @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 {@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();

    }

    /**

     * 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 "+provider.getName()+", ");

        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. Does a simple byte compare.

     *

     * @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.length != digestb.length) {

            return false;

        }

        int result = 0;

        // time-constant comparison

        for (int i = 0; i < digesta.length; i++) {

            result |= digesta[i] ^ digestb[i];

        }

        return result == 0;

    }

    /**

     * 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", "MD5", and so on).

     * See the MessageDigest section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#MessageDigest">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</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.

     *

     * @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.

     *

     * @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();

        }

    }