package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.StreamBlockCipher;
import org.bouncycastle.crypto.params.ParametersWithIV;
import org.bouncycastle.util.Arrays;

implements a Cipher-FeedBack (CFB) mode on top of a simple cipher.
/**
 * implements a Cipher-FeedBack (CFB) mode on top of a simple cipher.
 */
public class CFBBlockCipher
    extends StreamBlockCipher
{
    private byte[]          IV;
    private byte[]          cfbV;
    private byte[]          cfbOutV;
    private byte[]          inBuf;

    private int             blockSize;
    private BlockCipher     cipher = null;
    private boolean         encrypting;
    private int             byteCount;

    
Basic constructor.
Params:
cipher – the block cipher to be used as the basis of the
feedback mode.
bitBlockSize – the block size in bits (note: a multiple of 8)/**
     * Basic constructor.
     *
     * @param cipher the block cipher to be used as the basis of the
     * feedback mode.
     * @param bitBlockSize the block size in bits (note: a multiple of 8)
     */
    public CFBBlockCipher(
        BlockCipher cipher,
        int         bitBlockSize)
    {
        super(cipher);

        this.cipher = cipher;
        this.blockSize = bitBlockSize / 8;

        this.IV = new byte[cipher.getBlockSize()];
        this.cfbV = new byte[cipher.getBlockSize()];
        this.cfbOutV = new byte[cipher.getBlockSize()];
        this.inBuf = new byte[blockSize];
    }

    
Initialise the cipher and, possibly, the initialisation vector (IV).
If an IV isn't passed as part of the parameter, the IV will be all zeros.
An IV which is too short is handled in FIPS compliant fashion.
Params:
encrypting – if true the cipher is initialised for
 encryption, if false for decryption.
params – the key and other data required by the cipher.
Throws:
IllegalArgumentException – if the params argument is
inappropriate./**
     * Initialise the cipher and, possibly, the initialisation vector (IV).
     * If an IV isn't passed as part of the parameter, the IV will be all zeros.
     * An IV which is too short is handled in FIPS compliant fashion.
     *
     * @param encrypting if true the cipher is initialised for
     *  encryption, if false for decryption.
     * @param params the key and other data required by the cipher.
     * @exception IllegalArgumentException if the params argument is
     * inappropriate.
     */
    public void init(
        boolean             encrypting,
        CipherParameters    params)
        throws IllegalArgumentException
    {
        this.encrypting = encrypting;
        
        if (params instanceof ParametersWithIV)
        {
            ParametersWithIV ivParam = (ParametersWithIV)params;
            byte[]      iv = ivParam.getIV();

            if (iv.length < IV.length)
            {
                // prepend the supplied IV with zeros (per FIPS PUB 81)
                System.arraycopy(iv, 0, IV, IV.length - iv.length, iv.length);
                for (int i = 0; i < IV.length - iv.length; i++)
                {
                    IV[i] = 0;
                }
            }
            else
            {
                System.arraycopy(iv, 0, IV, 0, IV.length);
            }

            reset();

            // if null it's an IV changed only.
            if (ivParam.getParameters() != null)
            {
                cipher.init(true, ivParam.getParameters());
            }
        }
        else
        {
            reset();

            // if it's null, key is to be reused.
            if (params != null)
            {
                cipher.init(true, params);
            }
        }
    }

    
return the algorithm name and mode.
Returns:
the name of the underlying algorithm followed by "/CFB"
and the block size in bits./**
     * return the algorithm name and mode.
     *
     * @return the name of the underlying algorithm followed by "/CFB"
     * and the block size in bits.
     */
    public String getAlgorithmName()
    {
        return cipher.getAlgorithmName() + "/CFB" + (blockSize * 8);
    }

    protected byte calculateByte(byte in)
          throws DataLengthException, IllegalStateException
    {
        return (encrypting) ? encryptByte(in) : decryptByte(in);
    }

    private byte encryptByte(byte in)
    {
        if (byteCount == 0)
        {
            cipher.processBlock(cfbV, 0, cfbOutV, 0);
        }

        byte rv = (byte)(cfbOutV[byteCount] ^ in);
        inBuf[byteCount++] = rv;

        if (byteCount == blockSize)
        {
            byteCount = 0;

            System.arraycopy(cfbV, blockSize, cfbV, 0, cfbV.length - blockSize);
            System.arraycopy(inBuf, 0, cfbV, cfbV.length - blockSize, blockSize);
        }

        return rv;
    }

    private byte decryptByte(byte in)
    {
        if (byteCount == 0)
        {
            cipher.processBlock(cfbV, 0, cfbOutV, 0);
        }

        inBuf[byteCount] = in;
        byte rv = (byte)(cfbOutV[byteCount++] ^ in);

        if (byteCount == blockSize)
        {
            byteCount = 0;

            System.arraycopy(cfbV, blockSize, cfbV, 0, cfbV.length - blockSize);
            System.arraycopy(inBuf, 0, cfbV, cfbV.length - blockSize, blockSize);
        }

        return rv;
    }

    
return the block size we are operating at.
Returns:
the block size we are operating at (in bytes)./**
     * return the block size we are operating at.
     *
     * @return the block size we are operating at (in bytes).
     */
    public int getBlockSize()
    {
        return blockSize;
    }

    
Process one block of input from the array in and write it to
the out array.
Params:
in – the array containing the input data.
inOff – offset into the in array the data starts at.
out – the array the output data will be copied into.
outOff – the offset into the out array the output will start at.
Throws:
DataLengthException – if there isn't enough data in in, or
space in out.
IllegalStateException – if the cipher isn't initialised.
Returns:
the number of bytes processed and produced./**
     * Process one block of input from the array in and write it to
     * the out array.
     *
     * @param in the array containing the input data.
     * @param inOff offset into the in array the data starts at.
     * @param out the array the output data will be copied into.
     * @param outOff the offset into the out array the output will start at.
     * @exception DataLengthException if there isn't enough data in in, or
     * space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     * @return the number of bytes processed and produced.
     */
    public int processBlock(
        byte[]      in,
        int         inOff,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        processBytes(in, inOff, blockSize, out, outOff);

        return blockSize;
    }

    
Do the appropriate processing for CFB mode encryption.
Params:
in – the array containing the data to be encrypted.
inOff – offset into the in array the data starts at.
out – the array the encrypted data will be copied into.
outOff – the offset into the out array the output will start at.
Throws:
DataLengthException – if there isn't enough data in in, or
space in out.
IllegalStateException – if the cipher isn't initialised.
Returns:
the number of bytes processed and produced./**
     * Do the appropriate processing for CFB mode encryption.
     *
     * @param in the array containing the data to be encrypted.
     * @param inOff offset into the in array the data starts at.
     * @param out the array the encrypted data will be copied into.
     * @param outOff the offset into the out array the output will start at.
     * @exception DataLengthException if there isn't enough data in in, or
     * space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     * @return the number of bytes processed and produced.
     */
    public int encryptBlock(
        byte[]      in,
        int         inOff,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        processBytes(in, inOff, blockSize, out, outOff);

        return blockSize;
    }

    
Do the appropriate processing for CFB mode decryption.
Params:
in – the array containing the data to be decrypted.
inOff – offset into the in array the data starts at.
out – the array the encrypted data will be copied into.
outOff – the offset into the out array the output will start at.
Throws:
DataLengthException – if there isn't enough data in in, or
space in out.
IllegalStateException – if the cipher isn't initialised.
Returns:
the number of bytes processed and produced./**
     * Do the appropriate processing for CFB mode decryption.
     *
     * @param in the array containing the data to be decrypted.
     * @param inOff offset into the in array the data starts at.
     * @param out the array the encrypted data will be copied into.
     * @param outOff the offset into the out array the output will start at.
     * @exception DataLengthException if there isn't enough data in in, or
     * space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     * @return the number of bytes processed and produced.
     */
    public int decryptBlock(
        byte[]      in,
        int         inOff,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        processBytes(in, inOff, blockSize, out, outOff);

        return blockSize;
    }

    
Return the current state of the initialisation vector.
Returns:
current IV/**
     * Return the current state of the initialisation vector.
     *
     * @return current IV
     */
    public byte[] getCurrentIV()
    {
        return Arrays.clone(cfbV);
    }

    
reset the chaining vector back to the IV and reset the underlying
cipher.
/**
     * reset the chaining vector back to the IV and reset the underlying
     * cipher.
     */
    public void reset()
    {
        System.arraycopy(IV, 0, cfbV, 0, IV.length);
        Arrays.fill(inBuf, (byte)0);
        byteCount = 0;

        cipher.reset();
    }
}