package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;

Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode
on top of a simple cipher. This class assumes the IV has been prepended
to the data stream already, and just accomodates the reset after
(blockSize + 2) bytes have been read.

For further info see RFC 2440.
/**
 * Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode
 * on top of a simple cipher. This class assumes the IV has been prepended
 * to the data stream already, and just accomodates the reset after
 * (blockSize + 2) bytes have been read.
 * <p>
 * For further info see <a href="http://www.ietf.org/rfc/rfc2440.html">RFC 2440</a>.
 */
public class OpenPGPCFBBlockCipher
    implements BlockCipher
{
    private byte[] IV;
    private byte[] FR;
    private byte[] FRE;

    private BlockCipher cipher;

    private int count;
    private int blockSize;
    private boolean forEncryption;
    
    
Basic constructor.
Params:
cipher – the block cipher to be used as the basis of the
feedback mode./**
     * Basic constructor.
     *
     * @param cipher the block cipher to be used as the basis of the
     * feedback mode.
     */
    public OpenPGPCFBBlockCipher(
        BlockCipher cipher)
    {
        this.cipher = cipher;

        this.blockSize = cipher.getBlockSize();
        this.IV = new byte[blockSize];
        this.FR = new byte[blockSize];
        this.FRE = new byte[blockSize];
    }

    
return the underlying block cipher that we are wrapping.
Returns:
the underlying block cipher that we are wrapping./**
     * return the underlying block cipher that we are wrapping.
     *
     * @return the underlying block cipher that we are wrapping.
     */
    public BlockCipher getUnderlyingCipher()
    {
        return cipher;
    }
    
    
return the algorithm name and mode.
Returns:
the name of the underlying algorithm followed by "/PGPCFB"
and the block size in bits./**
     * return the algorithm name and mode.
     *
     * @return the name of the underlying algorithm followed by "/PGPCFB"
     * and the block size in bits.
     */
    public String getAlgorithmName()
    {
        return cipher.getAlgorithmName() + "/OpenPGPCFB";
    }
    
    
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 cipher.getBlockSize();
    }

    
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
    {
        return (forEncryption) ? encryptBlock(in, inOff, out, outOff) : decryptBlock(in, inOff, out, outOff);
    }
    
    
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()
    {
        count = 0;

        System.arraycopy(IV, 0, FR, 0, FR.length);

        cipher.reset();
    }

    
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:
forEncryption – 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 forEncryption 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 forEncryption,
        CipherParameters params)
        throws IllegalArgumentException
    {
        this.forEncryption = forEncryption;
     
        reset();

        cipher.init(true, params);
    }
    
    
Encrypt one byte of data according to CFB mode.
Params:
data – the byte to encrypt
blockOff – offset in the current block
Returns:
the encrypted byte/**
     * Encrypt one byte of data according to CFB mode.
     * @param data the byte to encrypt
     * @param blockOff offset in the current block
     * @return the encrypted byte
     */
    private byte encryptByte(byte data, int blockOff)
    {
        return (byte)(FRE[blockOff] ^ data);
    }
    
    
Do the appropriate processing for CFB IV 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 IV 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.
     */
    private int encryptBlock(
        byte[] in,
        int inOff,
        byte[] out,
        int outOff)
        throws DataLengthException, IllegalStateException
    {
        if ((inOff + blockSize) > in.length)
        {
            throw new DataLengthException("input buffer too short");
        }

        if ((outOff + blockSize) > out.length)
        {
            throw new DataLengthException("output buffer too short");
        }
        
        if (count > blockSize)
        {
            FR[blockSize - 2] = out[outOff] = encryptByte(in[inOff], blockSize - 2);
            FR[blockSize - 1] = out[outOff + 1] = encryptByte(in[inOff + 1], blockSize - 1);

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                FR[n - 2] = out[outOff + n] = encryptByte(in[inOff + n], n - 2);
            }
        }
        else if (count == 0)
        {
            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 0; n < blockSize; n++) 
            {
                FR[n] = out[outOff + n] = encryptByte(in[inOff + n], n);
            }
            
            count += blockSize;
        }
        else if (count == blockSize)
        {
            cipher.processBlock(FR, 0, FRE, 0);

            out[outOff] = encryptByte(in[inOff], 0);
            out[outOff + 1] = encryptByte(in[inOff + 1], 1);

            //
            // do reset
            //
            System.arraycopy(FR, 2, FR, 0, blockSize - 2);
            System.arraycopy(out, outOff, FR, blockSize - 2, 2);

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                FR[n - 2] = out[outOff + n] = encryptByte(in[inOff + n], n - 2);
            }

            count += blockSize;
        }
        
        return blockSize;
    }

    
Do the appropriate processing for CFB IV 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 IV 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.
     */
    private int decryptBlock(
        byte[] in,
        int inOff,
        byte[] out,
        int outOff)
        throws DataLengthException, IllegalStateException
    {
        if ((inOff + blockSize) > in.length)
        {
            throw new DataLengthException("input buffer too short");
        }

        if ((outOff + blockSize) > out.length)
        {
            throw new DataLengthException("output buffer too short");
        }
        
        if (count > blockSize)
        {
            byte inVal = in[inOff];
            FR[blockSize - 2] = inVal;
            out[outOff] = encryptByte(inVal, blockSize - 2);

            inVal = in[inOff + 1];
            FR[blockSize - 1] = inVal;
            out[outOff + 1] = encryptByte(inVal, blockSize - 1);

            cipher.processBlock(FR, 0, FRE, 0);
            
            for (int n = 2; n < blockSize; n++) 
            {
                inVal = in[inOff + n];
                FR[n - 2] = inVal;
                out[outOff + n] = encryptByte(inVal, n - 2);
            }
        } 
        else if (count == 0)
        {
            cipher.processBlock(FR, 0, FRE, 0);
            
            for (int n = 0; n < blockSize; n++) 
            {
                FR[n] = in[inOff + n];
                out[n] = encryptByte(in[inOff + n], n);
            }
            
            count += blockSize;
        }
        else if (count == blockSize)
        {
            cipher.processBlock(FR, 0, FRE, 0);

            byte inVal1 = in[inOff];
            byte inVal2 = in[inOff + 1];
            out[outOff    ] = encryptByte(inVal1, 0);
            out[outOff + 1] = encryptByte(inVal2, 1);
            
            System.arraycopy(FR, 2, FR, 0, blockSize - 2);

            FR[blockSize - 2] = inVal1;
            FR[blockSize - 1] = inVal2;

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                byte inVal = in[inOff + n];
                FR[n - 2] = inVal;
                out[outOff + n] = encryptByte(inVal, n - 2);
            }

            count += blockSize;
        }
        
        return blockSize;
    }
}