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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.4.
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package org.bouncycastle.crypto.io;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.bouncycastle.crypto.BufferedBlockCipher;
import org.bouncycastle.crypto.StreamCipher;

public class CipherOutputStream
    extends FilterOutputStream
{
    private BufferedBlockCipher bufferedBlockCipher;
    private StreamCipher streamCipher;

    private byte[] oneByte = new byte[1];
    private byte[] buf;

    /**
     * Constructs a CipherOutputStream from an OutputStream and a
     * BufferedBlockCipher.
     */
    public CipherOutputStream(
        OutputStream os,
        BufferedBlockCipher cipher)
    {
        super(os);
        this.bufferedBlockCipher = cipher;
        this.buf = new byte[cipher.getBlockSize()];
    }

    /**
     * Constructs a CipherOutputStream from an OutputStream and a
     * BufferedBlockCipher.
     */
    public CipherOutputStream(
        OutputStream os,
        StreamCipher cipher)
    {
        super(os);
        this.streamCipher = cipher;
    }

    /**
     * Writes the specified byte to this output stream.
     *
     * @param b the byte.
     * @exception java.io.IOException if an I/O error occurs.
     */
    public void write(
        int b)
        throws IOException
    {
        oneByte[0] = (byte)b;

        if (bufferedBlockCipher != null)
        {
            int len = bufferedBlockCipher.processBytes(oneByte, 0, 1, buf, 0);

            if (len != 0)
            {
                out.write(buf, 0, len);
            }
        }
        else
        {
            out.write(streamCipher.returnByte((byte)b));
        }
    }

    /**
     * Writes b.length bytes from the specified byte array
     * to this output stream.
     * 
     * The write method of
     * CipherOutputStream calls the write
     * method of three arguments with the three arguments
     * b, 0, and b.length.
     *
     * @param b the data.
     * @exception java.io.IOException if an I/O error occurs.
     * @see #write(byte[], int, int)
     */
    public void write(
        byte[] b)
        throws IOException
    {
        write(b, 0, b.length);
    }

    /**
     * Writes len bytes from the specified byte array
     * starting at offset off to this output stream.
     *
     * @param b the data.
     * @param off the start offset in the data.
     * @param len the number of bytes to write.
     * @exception java.io.IOException if an I/O error occurs.
     */
    public void write(
        byte[] b,
        int off,
        int len)
        throws IOException
    {
        if (bufferedBlockCipher != null)
        {
            byte[] buf = new byte[bufferedBlockCipher.getOutputSize(len)];

            int outLen = bufferedBlockCipher.processBytes(b, off, len, buf, 0);

            if (outLen != 0)
            {
                out.write(buf, 0, outLen);
            }
        }
        else
        {
            byte[] buf = new byte[len];

            streamCipher.processBytes(b, off, len, buf, 0);

            out.write(buf, 0, len);
        }
    }

    /**
     * Flushes this output stream by forcing any buffered output bytes
     * that have already been processed by the encapsulated cipher object
     * to be written out.
     *
     * 

     * Any bytes buffered by the encapsulated cipher
     * and waiting to be processed by it will not be written out. For example,
     * if the encapsulated cipher is a block cipher, and the total number of
     * bytes written using one of the write methods is less than
     * the cipher's block size, no bytes will be written out.
     *
     * @exception java.io.IOException if an I/O error occurs.
     */
    public void flush()
        throws IOException
    {
        super.flush();
    }

    /**
     * Closes this output stream and releases any system resources
     * associated with this stream.
     * 

     * This method invokes the doFinal method of the encapsulated
     * cipher object, which causes any bytes buffered by the encapsulated
     * cipher to be processed. The result is written out by calling the
     * flush method of this output stream.
     * 
     * This method resets the encapsulated cipher object to its initial state
     * and calls the close method of the underlying output
     * stream.
     *
     * @exception java.io.IOException if an I/O error occurs.
     */
    public void close()
        throws IOException
    {
        try
        {
            if (bufferedBlockCipher != null)
            {
                byte[] buf = new byte[bufferedBlockCipher.getOutputSize(0)];

                int outLen = bufferedBlockCipher.doFinal(buf, 0);

                if (outLen != 0)
                {
                    out.write(buf, 0, outLen);
                }
            }
        }
        catch (Exception e)
        {
            throw new IOException("Error closing stream: " + e.toString());
        }

        flush();

        super.close();
    }
}