SHAInterleave.java Source code

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Here is the source code for SHAInterleave.java

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/*
 * JBoss, Home of Professional Open Source.
 * Copyright 2008, Red Hat Middleware LLC, and individual contributors
 * as indicated by the @author tags. See the copyright.txt file in the
 * distribution for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

import java.io.ByteArrayOutputStream;
import java.security.MessageDigest;
import java.security.MessageDigestSpi;
import java.security.NoSuchAlgorithmException;
import java.security.ProviderException;

/** The SHA_Interleave algorithm as described in section 3.1 of RFC2945. This
 needs an SHA MessageDigest provider to function.
    
@author Scott.Stark@jboss.org
@version $Revision: 85945 $
*/
public class SHAInterleave extends MessageDigestSpi {
    private static final int SHA_HASH_LEN = 20;

    private ByteArrayOutputStream evenBytes;
    private ByteArrayOutputStream oddBytes;
    private int count;
    private boolean skipLeadingZeros;
    private MessageDigest sha;

    /** Creates a new instance of SHAInterleave
     @exception ProviderException thrown if MessageDigest.getInstance("SHA")
     throws a NoSuchAlgorithmException.
     */
    public SHAInterleave() {
        try {
            sha = MessageDigest.getInstance("SHA");
        } catch (NoSuchAlgorithmException e) {
            throw new ProviderException("Failed to obtain SHA MessageDigest");
        }
        evenBytes = new ByteArrayOutputStream();
        oddBytes = new ByteArrayOutputStream();
        engineReset();
    }

    protected int engineGetDigestLength() {
        return 2 * SHA_HASH_LEN;
    }

    /**
     * Completes the digest computation by performing final
     * operations such as padding. Once <code>engineDigest</code> has
     * been called, the engine should be reset (see
     * {@link #engineReset() engineReset}).
     * Resetting is the responsibility of the
     * engine implementor.
     *
     * @return the array of bytes for the resulting digest value.
     */
    protected byte[] engineDigest() {
        byte[] E = evenBytes.toByteArray();
        byte[] G = sha.digest(E);
        // If the count is odd, drop the first byte
        byte[] F = oddBytes.toByteArray();
        int offset = 0;
        if (count % 2 == 1)
            offset = 1;
        sha.reset();
        sha.update(F, offset, F.length - offset);
        byte[] H = sha.digest();
        int length = G.length + H.length;
        byte[] digest = new byte[length];
        for (int i = 0; i < G.length; ++i)
            digest[2 * i] = G[i];
        for (int i = 0; i < H.length; ++i)
            digest[2 * i + 1] = H[i];
        engineReset();
        return digest;
    }

    /**
     * Resets the digest for further use.
     */
    protected void engineReset() {
        skipLeadingZeros = true;
        count = 0;
        evenBytes.reset();
        oddBytes.reset();
        sha.reset();
    }

    /**
     * Updates the digest using the specified byte.
     *
     * @param input the byte to use for the update.
     */
    protected void engineUpdate(byte input) {
        if (skipLeadingZeros == true && input == 0)
            return;
        skipLeadingZeros = false;
        if (count % 2 == 0)
            evenBytes.write(input);
        else
            oddBytes.write(input);
        count++;
    }

    /**
     * Updates the digest using the specified array of bytes,
     * starting at the specified offset.
     *
     * @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 input of bytes to use, starting at
     * <code>offset</code>.
     */
    protected void engineUpdate(byte[] input, int offset, int len) {
        for (int i = offset; i < offset + len; i++)
            engineUpdate(input[i]);
    }

}