Java 1.2 How-To/JavaHowTo.iso/3rdParty/jbuilder/unsupported/JDK1.2beta3/SOURCE/SRC.ZIP/java/security/MessageDigestSpi.java

Java Source | 1998-03-20 | 5.2 KB | 161 lines

/*
 * @(#)MessageDigestSpi.java    1.3 98/03/18
 *
 * Copyright 1997, 1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

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;

/**
 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
 * for the <code>MessageDigest</code> class, which provides the functionality
 * of a message digest algorithm, such as MD5 or SHA. Message digests are
 * secure one-way hash functions that take arbitrary-sized data and output a
 * fixed-length hash value.
 *
 * <p> All the abstract methods in this class must be implemented by a
 * cryptographic service provider who wishes to supply the implementation
 * of a particular message digest algorithm.
 *
 * <p> Implementations are free to implement the Cloneable interface.
 *
 * @author Benjamin Renaud
 *
 * @version 1.3 98/03/18
 *
 * @see MessageDigest
 */

public abstract class MessageDigestSpi {

    /**
     * Returns the digest length in bytes.
     *
     * <p>This concrete method has been added to this previously-defined
     * abstract class. (For backwards compatibility, it cannot be abstract.)
     *
     * <p>The default behavior is to return 0.
     *
     * <p>This method may be overridden by a provider to return the digest
     * length.
     *
     * @return the digest length in bytes.
     *
     * @since JDK1.2
     */
    protected int engineGetDigestLength() {
    return 0;
    }

    /**
     * Updates the digest using the specified byte.
     *
     * @param input the byte to use for the update.
     */
    protected abstract void engineUpdate(byte input);

    /**
     * Updates the digest using the specified array of bytes,
     * starting at the specified offset. This should be a no-op if
     * the digest has been finalized.
     *
     * @param input the array of bytes to use for the update.
     *
     * @param offset the offset to start from in the array of bytes.
     *
     * @param len the number of bytes to use, starting at
     * <code>offset</code>.
     */
    protected abstract void engineUpdate(byte[] input, int offset, int len);

    /**
     * Completes the hash computation by performing final
     * operations such as padding. Once <code>engineDigest</code> has
     * been called, the engine should be reset (see <a href =
     * "#engineReset">engineReset</a>).  Resetting is the responsibility of the
     * engine implementor.
     *
     * @return the array of bytes for the resulting hash value.
     */
    protected abstract byte[] engineDigest();

    /**
     * Completes the hash computation by performing final
     * operations such as padding. Once <code>engineDigest</code> has
     * been called, the engine should be reset (see <a href =
     * "#engineReset">engineReset</a>).  Resetting is the responsibility of the
     * engine implementor.
     *
     * This method should be abstract, but we leave it concrete for
     * binary compatibility.  Knowledgeable providers should override this
     * method.
     *
     * @param buf the output buffer in which to store the digest
     *
     * @param offset offset to start from in the output buffer
     *
     * @param len number of bytes within buf allotted for the digest.
     * Both this default implementation and the SUN provider do not
     * return partial digests.  The presence of this parameter is solely
     * for consistency in our API's.  If the value of this parameter is less
     * than the actual digest length, the method will throw a DigestException.
     * This parameter is ignored if its value is greater than or equal to
     * the actual digest length.
     *
     * @return the length of the digest stored in the output buffer.
     *
     * @exception DigestException if an error occurs.
     *
     * @since JDK1.2
     */
    protected int engineDigest(byte[] buf, int offset, int len)
                        throws DigestException {

    byte[] digest = engineDigest();
    if (len < digest.length)
        throw new DigestException("partial digests not returned");
    if (buf.length - offset < digest.length)
        throw new DigestException("insufficient space in the output "
                      + "buffer to store the digest");
    System.arraycopy(digest, 0, buf, offset, digest.length);
    return digest.length;
    }

    /**
     * Resets the digest for further use.
     */
    protected abstract void engineReset();

    /**
     * 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</code>.
     */
    public Object clone() throws CloneNotSupportedException {
    if (this instanceof Cloneable) {
        return super.clone();
    } else {
        throw new CloneNotSupportedException();
    }
    }
}