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;

implements the GOST 28147 OFB counter mode (GCTR).
/**
 * implements the GOST 28147 OFB counter mode (GCTR).
 */
public class GOFBBlockCipher
    extends StreamBlockCipher
{
    private byte[]          IV;
    private byte[]          ofbV;
    private byte[]          ofbOutV;
    private int             byteCount;

    private final int             blockSize;
    private final BlockCipher     cipher;

    boolean firstStep = true;
    int N3;
    int N4;
    static final int C1 = 16843012; //00000001000000010000000100000100
    static final int C2 = 16843009; //00000001000000010000000100000001


    
Basic constructor.
Params:
cipher – the block cipher to be used as the basis of the
counter mode (must have a 64 bit block size)./**
     * Basic constructor.
     *
     * @param cipher the block cipher to be used as the basis of the
     * counter mode (must have a 64 bit block size).
     */
    public GOFBBlockCipher(
        BlockCipher cipher)
    {
        super(cipher);

        this.cipher = cipher;
        this.blockSize = cipher.getBlockSize();
        
        if (blockSize != 8)
        {
            throw new IllegalArgumentException("GCTR only for 64 bit block ciphers");
        }

        this.IV = new byte[cipher.getBlockSize()];
        this.ofbV = new byte[cipher.getBlockSize()];
        this.ofbOutV = new byte[cipher.getBlockSize()];
    }

    
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, //ignored by this CTR mode
        CipherParameters    params)
        throws IllegalArgumentException
    {
        firstStep = true;
        N3 = 0;
        N4 = 0;

        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 params is null we reuse the current working key.
            if (ivParam.getParameters() != null)
            {
                cipher.init(true, ivParam.getParameters());
            }
        }
        else
        {
            reset();

            // if params is null we reuse the current working key.
            if (params != null)
            {
                cipher.init(true, params);
            }
        }
    }

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

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

    
reset the feedback vector back to the IV and reset the underlying
cipher.
/**
     * reset the feedback vector back to the IV and reset the underlying
     * cipher.
     */
    public void reset()
    {
        firstStep = true;
        N3 = 0;
        N4 = 0;
        System.arraycopy(IV, 0, ofbV, 0, IV.length);
        byteCount = 0;
        cipher.reset();
    }

    //array of bytes to type int
    private int bytesToint(
        byte[]  in,
        int     inOff)
    {
        return  ((in[inOff + 3] << 24) & 0xff000000) + ((in[inOff + 2] << 16) & 0xff0000) +
                ((in[inOff + 1] << 8) & 0xff00) + (in[inOff] & 0xff);
    }

    //int to array of bytes
    private void intTobytes(
            int     num,
            byte[]  out,
            int     outOff)
    {
            out[outOff + 3] = (byte)(num >>> 24);
            out[outOff + 2] = (byte)(num >>> 16);
            out[outOff + 1] = (byte)(num >>> 8);
            out[outOff] =     (byte)num;
    }

    protected byte calculateByte(byte b)
    {
        if (byteCount == 0)
        {
            if (firstStep)
            {
                firstStep = false;
                cipher.processBlock(ofbV, 0, ofbOutV, 0);
                N3 = bytesToint(ofbOutV, 0);
                N4 = bytesToint(ofbOutV, 4);
            }
            N3 += C2;
            N4 += C1;
            if (N4 < C1)  // addition is mod (2**32 - 1)
            {
                if (N4 > 0)
                {
                    N4++;
                }
            }
            intTobytes(N3, ofbV, 0);
            intTobytes(N4, ofbV, 4);

            cipher.processBlock(ofbV, 0, ofbOutV, 0);
        }

        byte rv = (byte)(ofbOutV[byteCount++] ^ b);

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

            //
            // change over the input block.
            //
            System.arraycopy(ofbV, blockSize, ofbV, 0, ofbV.length - blockSize);
            System.arraycopy(ofbOutV, 0, ofbV, ofbV.length - blockSize, blockSize);
        }

        return rv;
    }
}