http://www.bouncycastle.org/java.html: 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 1.5. 
package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.BufferedBlockCipher;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.InvalidCipherTextException;


A wrapper class that allows block ciphers to be used to process data in
a piecemeal fashion with PKCS5/PKCS7 padding. The PaddedBlockCipher
outputs a block only when the buffer is full and more data is being added,
or on a doFinal (unless the current block in the buffer is a pad block).
The padding mechanism used is the one outlined in PKCS5/PKCS7.

Deprecated:use org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher instead.
/**
 * A wrapper class that allows block ciphers to be used to process data in
 * a piecemeal fashion with PKCS5/PKCS7 padding. The PaddedBlockCipher
 * outputs a block only when the buffer is full and more data is being added,
 * or on a doFinal (unless the current block in the buffer is a pad block).
 * The padding mechanism used is the one outlined in PKCS5/PKCS7.
 *
 * @deprecated use org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher instead.
 */
public class PaddedBlockCipher
    extends BufferedBlockCipher
{
    
Create a buffered block cipher with, or without, padding.

Params:
  • cipher – the underlying block cipher this buffering object wraps.
/**
     * Create a buffered block cipher with, or without, padding.
     *
     * @param cipher the underlying block cipher this buffering object wraps.
     */
    public PaddedBlockCipher(
        BlockCipher     cipher)
    {
        this.cipher = cipher;

        buf = new byte[cipher.getBlockSize()];
        bufOff = 0;
    }

    
return the size of the output buffer required for an update plus a
doFinal with an input of len bytes.

Params:
  • len – the length of the input.
Returns:the space required to accommodate a call to update and doFinal
with len bytes of input.
/**
     * return the size of the output buffer required for an update plus a
     * doFinal with an input of len bytes.
     *
     * @param len the length of the input.
     * @return the space required to accommodate a call to update and doFinal
     * with len bytes of input.
     */
    public int getOutputSize(
        int len)
    {
        int total       = len + bufOff;
        int leftOver    = total % buf.length;

        if (leftOver == 0)
        {
            if (forEncryption)
            {
                return total + buf.length;
            }

            return total;
        }

        return total - leftOver + buf.length;
    }

    
return the size of the output buffer required for an update 
an input of len bytes.

Params:
  • len – the length of the input.
Returns:the space required to accommodate a call to update
with len bytes of input.
/**
     * return the size of the output buffer required for an update 
     * an input of len bytes.
     *
     * @param len the length of the input.
     * @return the space required to accommodate a call to update
     * with len bytes of input.
     */
    public int getUpdateOutputSize(
        int len)
    {
        int total       = len + bufOff;
        int leftOver    = total % buf.length;

        if (leftOver == 0)
        {
            return total - buf.length;
        }

        return total - leftOver;
    }

    
process a single byte, producing an output block if neccessary.

Params:
  • in – the input byte.
  • out – the space for any output that might be produced.
  • outOff – the offset from which the output will be copied.
Throws:
/**
     * process a single byte, producing an output block if neccessary.
     *
     * @param in the input byte.
     * @param out the space for any output that might be produced.
     * @param outOff the offset from which the output will be copied.
     * @exception DataLengthException if there isn't enough space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     */
    public int processByte(
        byte        in,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        int         resultLen = 0;

        if (bufOff == buf.length)
        {
            resultLen = cipher.processBlock(buf, 0, out, outOff);
            bufOff = 0;
        }

        buf[bufOff++] = in;

        return resultLen;
    }

    
process an array of bytes, producing output if necessary.

Params:
  • in – the input byte array.
  • inOff – the offset at which the input data starts.
  • len – the number of bytes to be copied out of the input array.
  • out – the space for any output that might be produced.
  • outOff – the offset from which the output will be copied.
Throws:
/**
     * process an array of bytes, producing output if necessary.
     *
     * @param in the input byte array.
     * @param inOff the offset at which the input data starts.
     * @param len the number of bytes to be copied out of the input array.
     * @param out the space for any output that might be produced.
     * @param outOff the offset from which the output will be copied.
     * @exception DataLengthException if there isn't enough space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     */
    public int processBytes(
        byte[]      in,
        int         inOff,
        int         len,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        if (len < 0)
        {
            throw new IllegalArgumentException("Can't have a negative input length!");
        }

        int blockSize   = getBlockSize();
        int length      = getUpdateOutputSize(len);
        
        if (length > 0)
        {
            if ((outOff + length) > out.length)
            {
                throw new DataLengthException("output buffer too short");
            }
        }

        int resultLen = 0;
        int gapLen = buf.length - bufOff;

        if (len > gapLen)
        {
            System.arraycopy(in, inOff, buf, bufOff, gapLen);

            resultLen += cipher.processBlock(buf, 0, out, outOff);

            bufOff = 0;
            len -= gapLen;
            inOff += gapLen;

            while (len > buf.length)
            {
                resultLen += cipher.processBlock(in, inOff, out, outOff + resultLen);

                len -= blockSize;
                inOff += blockSize;
            }
        }

        System.arraycopy(in, inOff, buf, bufOff, len);

        bufOff += len;

        return resultLen;
    }

    
Process the last block in the buffer. If the buffer is currently
full and padding needs to be added a call to doFinal will produce
2 * getBlockSize() bytes.

Params:
  • out – the array the block currently being held is copied into.
  • outOff – the offset at which the copying starts.
Throws:
/**
     * Process the last block in the buffer. If the buffer is currently
     * full and padding needs to be added a call to doFinal will produce
     * 2 * getBlockSize() bytes.
     *
     * @param out the array the block currently being held is copied into.
     * @param outOff the offset at which the copying starts.
     * @exception DataLengthException if there is insufficient space in out for
     * the output or we are decrypting and the input is not block size aligned.
     * @exception IllegalStateException if the underlying cipher is not
     * initialised.
     * @exception InvalidCipherTextException if padding is expected and not found.
     */
    public int doFinal(
        byte[]  out,
        int     outOff)
        throws DataLengthException, IllegalStateException, InvalidCipherTextException
    {
        int blockSize = cipher.getBlockSize();
        int resultLen = 0;

        if (forEncryption)
        {
            if (bufOff == blockSize)
            {
                if ((outOff + 2 * blockSize) > out.length)
                {
                    throw new DataLengthException("output buffer too short");
                }

                resultLen = cipher.processBlock(buf, 0, out, outOff);
                bufOff = 0;
            }

            //
            // add PKCS7 padding
            //
            byte code = (byte)(blockSize - bufOff);

            while (bufOff < blockSize)
            {
                buf[bufOff] = code;
                bufOff++;
            }

            resultLen += cipher.processBlock(buf, 0, out, outOff + resultLen);
        }
        else
        {
            if (bufOff == blockSize)
            {
                resultLen = cipher.processBlock(buf, 0, buf, 0);
                bufOff = 0;
            }
            else
            {
                throw new DataLengthException("last block incomplete in decryption");
            }

            //
            // remove PKCS7 padding
            //
            int count = buf[blockSize - 1] & 0xff;

            if ((count < 0) || (count > blockSize))
            {
                throw new InvalidCipherTextException("pad block corrupted");
            }

            resultLen -= count;

            System.arraycopy(buf, 0, out, outOff, resultLen);
        }

        reset();

        return resultLen;
    }
}