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;

An implementation of the CFB mode for GOST 3412 2015 cipher.
See  GOST R 3413 2015
/**
 * An implementation of the CFB mode for GOST 3412 2015 cipher.
 * See  <a href="http://www.tc26.ru/standard/gost/GOST_R_3413-2015.pdf">GOST R 3413 2015</a>
 */
public class G3413CFBBlockCipher
    extends StreamBlockCipher
{
    private final int s;
    private int m;
    private int blockSize;
    private byte[] R;
    private byte[] R_init;
    private BlockCipher cipher;
    private boolean forEncryption;
    private boolean initialized = false;

    private byte[] gamma;
    private byte[] inBuf;
    private int byteCount;

    
Base constructor.
Params:
cipher – base cipher/**
     * Base constructor.
     *
     * @param cipher base cipher
     */
    public G3413CFBBlockCipher(BlockCipher cipher)
    {
        this(cipher, cipher.getBlockSize() * 8);
    }

    
Base constructor with specific block size.
Params:
cipher – base cipher
bitBlockSize – basic unit (defined as s)/**
     * Base constructor with specific block size.
     *
     * @param cipher base cipher
     * @param bitBlockSize basic unit (defined as s)
     */
    public G3413CFBBlockCipher(BlockCipher cipher, int bitBlockSize)
    {
        super(cipher);

        if (bitBlockSize < 0 || bitBlockSize > cipher.getBlockSize() * 8)
        {
            throw new IllegalArgumentException("Parameter bitBlockSize must be in range 0 < bitBlockSize <= "
                            + cipher.getBlockSize() * 8);
        }

        this.blockSize = cipher.getBlockSize();
        this.cipher = cipher;
        this.s = bitBlockSize / 8;
        inBuf = new byte[getBlockSize()];
    }

    
Initialise the cipher and initialisation vector R.
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.
R_init = IV, and R1 = R_init
Params:
forEncryption – ignored because encryption and decryption are same
params –        the key and other data required by the cipher.
Throws:
IllegalArgumentException – /**
     * Initialise the cipher and initialisation vector R.
     * 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.
     * R_init = IV, and R1 = R_init
     *
     * @param forEncryption ignored because encryption and decryption are same
     * @param params        the key and other data required by the cipher.
     * @throws IllegalArgumentException
     */
    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 < blockSize)
            {
                throw new IllegalArgumentException("Parameter m must blockSize <= m");
            }
            m = iv.length;

            initArrays();

            R_init = Arrays.clone(iv);
            System.arraycopy(R_init, 0, R, 0, R_init.length);


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

            initArrays();
            System.arraycopy(R_init, 0, R, 0, R_init.length);


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

        initialized = true;
    }

    
allocate memory for R and R_init arrays
/**
     * allocate memory for R and R_init arrays
     */
    private void initArrays()
    {
        R = new byte[m];
        R_init = new byte[m];
    }

    
this method sets default values to s and m parameters:

s = blockSize; 

m = 2 * blockSize
/**
     * this method sets default values to <b>s</b> and <b>m</b> parameters:<br>
     * s = <b>blockSize</b>; <br>
     * m = <b>2 * blockSize</b>
     */
    private void setupDefaultParams()
    {
        this.m = 2 * blockSize;
    }


    public String getAlgorithmName()
    {
        return cipher.getAlgorithmName() + "/CFB" + (blockSize * 8);
    }

    public int getBlockSize()
    {
        return s;
    }

    public int processBlock(byte[] in, int inOff, byte[] out, int outOff)
        throws DataLengthException, IllegalStateException
    {
        this.processBytes(in, inOff, getBlockSize(), out, outOff);

        return getBlockSize();
    }

    protected byte calculateByte(byte in)
    {
        if (byteCount == 0)
        {
            gamma = createGamma();
        }

        byte rv = (byte)(gamma[byteCount] ^ in);
        inBuf[byteCount++] = (forEncryption) ? rv : in;

        if (byteCount == getBlockSize())
        {
            byteCount = 0;
            generateR(inBuf);
        }

        return rv;
    }

    
creating gamma value
Returns:
gamma/**
     * creating gamma value
     *
     * @return gamma
     */
    byte[] createGamma()
    {
        byte[] msb = GOST3413CipherUtil.MSB(R, blockSize);
        byte[] encryptedMsb = new byte[msb.length];
        cipher.processBlock(msb, 0, encryptedMsb, 0);
        return GOST3413CipherUtil.MSB(encryptedMsb, s);
    }

    
generate new R value
Params:
C – processed block/**
     * generate new R value
     *
     * @param C processed block
     */
    void generateR(byte[] C)
    {

        byte[] buf = GOST3413CipherUtil.LSB(R, m - s);
        System.arraycopy(buf, 0, R, 0, buf.length);
        System.arraycopy(C, 0, R, buf.length, m - buf.length);
    }

    
copy R_init into R and reset the underlying
cipher.
/**
     * copy R_init into R and reset the underlying
     * cipher.
     */
    public void reset()
    {

        byteCount = 0;
        Arrays.clear(inBuf);
        Arrays.clear(gamma);

        if (initialized)
        {
            System.arraycopy(R_init, 0, R, 0, R_init.length);

            cipher.reset();
        }
    }
}