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A partial port of the Bouncycastle J2ME crypto library with parts taken from GWTx.

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package com.googlecode.gwt.crypto.bouncycastle.paddings;

import com.googlecode.gwt.crypto.bouncycastle.InvalidCipherTextException;
import com.googlecode.gwt.crypto.util.SecureRandom;

/**
 * A padder that adds NULL byte padding to a block.
 */
public class ZeroBytePadding
    implements BlockCipherPadding
{
    /**
     * Initialise the padder.
     *
     * @param random - a SecureRandom if available.
     */
    @Override
	public void init(SecureRandom random)
        throws IllegalArgumentException
    {
        // nothing to do.
    }

    /**
     * Return the name of the algorithm the padder implements.
     *
     * @return the name of the algorithm the padder implements.
     */
    @Override
	public String getPaddingName()
    {
        return "ZeroByte";
    }

    /**
     * add the pad bytes to the passed in block, returning the
     * number of bytes added.
     */
    @Override
	public int addPadding(
        byte[]  in,
        int     inOff)
    {
        int added = (in.length - inOff);

        while (inOff < in.length)
        {
            in[inOff] = (byte) 0;
            inOff++;
        }

        return added;
    }

    /**
     * return the number of pad bytes present in the block.
     */
    @Override
	public int padCount(byte[] in)
        throws InvalidCipherTextException
    {
        int count = in.length;

        while (count > 0)
        {
            if (in[count - 1] != 0)
            {
                break;
            }

            count--;
        }

        return in.length - count;
    }

}