package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.OutputLengthException;
import org.bouncycastle.crypto.params.ParametersWithIV;

Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode on top of a simple cipher. For further info see RFC 2440.
/**
 * Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode on top of a simple cipher. For further info see <a href="http://www.ietf.org/rfc/rfc2440.html">RFC 2440</a>.
 */
public class PGPCFBBlockCipher
    implements BlockCipher
{
    private byte[] IV;
    private byte[] FR;
    private byte[] FRE;
    private byte[] tmp;

    private BlockCipher cipher;

    private int count;
    private int blockSize;
    private boolean forEncryption;
    
    private boolean inlineIv; // if false we don't need to prepend an IV

    
Basic constructor.
Params:
cipher – the block cipher to be used as the basis of the
feedback mode.
inlineIv – if true this is for PGP CFB with a prepended iv./**
     * Basic constructor.
     *
     * @param cipher the block cipher to be used as the basis of the
     * feedback mode.
     * @param inlineIv if true this is for PGP CFB with a prepended iv.
     */
    public PGPCFBBlockCipher(
        BlockCipher cipher,
        boolean     inlineIv)
    {
        this.cipher = cipher;
        this.inlineIv = inlineIv;

        this.blockSize = cipher.getBlockSize();
        this.IV = new byte[blockSize];
        this.FR = new byte[blockSize];
        this.FRE = new byte[blockSize];
        this.tmp = 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()
    {
        if (inlineIv)
        {
            return cipher.getAlgorithmName() + "/PGPCFBwithIV";
        }
        else
        {
            return cipher.getAlgorithmName() + "/PGPCFB";
        }
    }
    
    
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
    {
        if (inlineIv)
        {
            return (forEncryption) ? encryptBlockWithIV(in, inOff, out, outOff) : decryptBlockWithIV(in, inOff, out, outOff);
        }
        else
        {
            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;

        for (int i = 0; i != FR.length; i++)
        {
            if (inlineIv)
            {
                FR[i] = 0;
            }
            else
            {
                FR[i] = IV[i]; // if simple mode, key is IV (even if this is zero)
            }
        }

        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;
     
        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();

                cipher.init(true, ivParam.getParameters());
        }
        else
        {
                reset();

                cipher.init(true, params);
        }
    }
    
    
Encrypt one byte of data according to CFB mode.
Params:
data – the byte to encrypt
blockOff – where am i in the current block, determines when to resync the block
@returns
the encrypted byte/**
     * Encrypt one byte of data according to CFB mode.
     * @param data the byte to encrypt
     * @param blockOff where am i in the current block, determines when to resync the block
     * @returns 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 encryptBlockWithIV(
        byte[] in,
        int inOff,
        byte[] out,
        int outOff)
        throws DataLengthException, IllegalStateException
    {
        if ((inOff + blockSize) > in.length)
        {
            throw new DataLengthException("input buffer too short");
        }

        if (count == 0)
        {
            if ((outOff + 2 * blockSize + 2) > out.length)
            {
                throw new OutputLengthException("output buffer too short");
            }

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

            for (int n = 0; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(IV[n], n);
            }
            
            System.arraycopy(out, outOff, FR, 0, blockSize);

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

            out[outOff + blockSize] = encryptByte(IV[blockSize - 2], 0);
            out[outOff + blockSize + 1] = encryptByte(IV[blockSize - 1], 1);

            System.arraycopy(out, outOff + 2, FR, 0, blockSize);
            
            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 0; n < blockSize; n++) 
            {
                out[outOff + blockSize + 2 + n] = encryptByte(in[inOff + n], n);
            }

            System.arraycopy(out, outOff + blockSize + 2, FR, 0, blockSize);

            count += 2 * blockSize + 2;

            return 2 * blockSize + 2;
        }
        else if (count >= blockSize + 2)
        {
            if ((outOff + blockSize) > out.length)
            {
                throw new OutputLengthException("output buffer too short");
            }

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

            for (int n = 0; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(in[inOff + n], n);
            }
            
            System.arraycopy(out, outOff, FR, 0, 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 decryptBlockWithIV(
        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 OutputLengthException("output buffer too short");
        }
        
        if (count == 0)
        {
            for (int n = 0; n < blockSize; n++) 
            {
                FR[n] = in[inOff + n];
            }
            
            cipher.processBlock(FR, 0, FRE, 0);

            count += blockSize;

            return 0;
        }
        else if (count == blockSize)
        {
            // copy in buffer so that this mode works if in and out are the same 
            System.arraycopy(in, inOff, tmp, 0, blockSize);
        
            System.arraycopy(FR, 2, FR, 0, blockSize - 2);
            
            FR[blockSize - 2] = tmp[0];
            FR[blockSize - 1] = tmp[1];

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

            for (int n = 0; n < blockSize - 2; n++) 
            {
                out[outOff + n] = encryptByte(tmp[n + 2], n);
            }

            System.arraycopy(tmp, 2, FR, 0, blockSize - 2);

            count += 2;

            return blockSize - 2;
        }
        else if (count >= blockSize + 2)
        {
            // copy in buffer so that this mode works if in and out are the same 
            System.arraycopy(in, inOff, tmp, 0, blockSize);

            out[outOff + 0] = encryptByte(tmp[0], blockSize - 2);
            out[outOff + 1] = encryptByte(tmp[1], blockSize - 1);

            System.arraycopy(tmp, 0, FR, blockSize - 2, 2);

            cipher.processBlock(FR, 0, FRE, 0);
            
            for (int n = 0; n < blockSize - 2; n++) 
            {
                out[outOff + n + 2] = encryptByte(tmp[n + 2], n);
            }
            
            System.arraycopy(tmp, 2, FR, 0, blockSize - 2);
            
        } 
        
        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.
     */
    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 OutputLengthException("output buffer too short");
        }
        
        cipher.processBlock(FR, 0, FRE, 0);
        for (int n = 0; n < blockSize; n++) 
        {
            out[outOff + n] = encryptByte(in[inOff + n], n);
        }
        
        for (int n = 0; n < blockSize; n++) 
        {
            FR[n] = out[outOff + n];
        }
        
        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.
     */
    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 OutputLengthException("output buffer too short");
        }
        
        cipher.processBlock(FR, 0, FRE, 0);
        for (int n = 0; n < blockSize; n++) 
        {
            out[outOff + n] = encryptByte(in[inOff + n], n);
        }
        
        for (int n = 0; n < blockSize; n++) 
        {
            FR[n] = in[inOff + n];
        }
        
        return blockSize;
        
    }
}