package org.bouncycastle.crypto.engines;

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.StreamCipher;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;

Implementation of Martin Hell's, Thomas Johansson's and Willi Meier's stream cipher, Grain v1.
/** * Implementation of Martin Hell's, Thomas Johansson's and Willi Meier's stream * cipher, Grain v1. */
public class Grainv1Engine implements StreamCipher {
Constants
/** * Constants */
private static final int STATE_SIZE = 5;
Variables to hold the state of the engine during encryption and decryption
/** * Variables to hold the state of the engine during encryption and * decryption */
private byte[] workingKey; private byte[] workingIV; private byte[] out; private int[] lfsr; private int[] nfsr; private int output; private int index = 2; private boolean initialised = false; public String getAlgorithmName() { return "Grain v1"; }
Initialize a Grain v1 cipher.
Params:
  • forEncryption – Whether or not we are for encryption.
  • params – The parameters required to set up the cipher.
Throws:
/** * Initialize a Grain v1 cipher. * * @param forEncryption Whether or not we are for encryption. * @param params The parameters required to set up the cipher. * @throws IllegalArgumentException If the params argument is inappropriate. */
public void init(boolean forEncryption, CipherParameters params) throws IllegalArgumentException { /** * Grain encryption and decryption is completely symmetrical, so the * 'forEncryption' is irrelevant. */ if (!(params instanceof ParametersWithIV)) { throw new IllegalArgumentException( "Grain v1 Init parameters must include an IV"); } ParametersWithIV ivParams = (ParametersWithIV)params; byte[] iv = ivParams.getIV(); if (iv == null || iv.length != 8) { throw new IllegalArgumentException( "Grain v1 requires exactly 8 bytes of IV"); } if (!(ivParams.getParameters() instanceof KeyParameter)) { throw new IllegalArgumentException( "Grain v1 Init parameters must include a key"); } KeyParameter key = (KeyParameter)ivParams.getParameters(); /** * Initialize variables. */ workingIV = new byte[key.getKey().length]; workingKey = new byte[key.getKey().length]; lfsr = new int[STATE_SIZE]; nfsr = new int[STATE_SIZE]; out = new byte[2]; System.arraycopy(iv, 0, workingIV, 0, iv.length); System.arraycopy(key.getKey(), 0, workingKey, 0, key.getKey().length); setKey(workingKey, workingIV); initGrain(); }
160 clocks initialization phase.
/** * 160 clocks initialization phase. */
private void initGrain() { for (int i = 0; i < 10; i++) { output = getOutput(); nfsr = shift(nfsr, getOutputNFSR() ^ lfsr[0] ^ output); lfsr = shift(lfsr, getOutputLFSR() ^ output); } initialised = true; }
Get output from non-linear function g(x).
Returns:Output from NFSR.
/** * Get output from non-linear function g(x). * * @return Output from NFSR. */
private int getOutputNFSR() { int b0 = nfsr[0]; int b9 = nfsr[0] >>> 9 | nfsr[1] << 7; int b14 = nfsr[0] >>> 14 | nfsr[1] << 2; int b15 = nfsr[0] >>> 15 | nfsr[1] << 1; int b21 = nfsr[1] >>> 5 | nfsr[2] << 11; int b28 = nfsr[1] >>> 12 | nfsr[2] << 4; int b33 = nfsr[2] >>> 1 | nfsr[3] << 15; int b37 = nfsr[2] >>> 5 | nfsr[3] << 11; int b45 = nfsr[2] >>> 13 | nfsr[3] << 3; int b52 = nfsr[3] >>> 4 | nfsr[4] << 12; int b60 = nfsr[3] >>> 12 | nfsr[4] << 4; int b62 = nfsr[3] >>> 14 | nfsr[4] << 2; int b63 = nfsr[3] >>> 15 | nfsr[4] << 1; return (b62 ^ b60 ^ b52 ^ b45 ^ b37 ^ b33 ^ b28 ^ b21 ^ b14 ^ b9 ^ b0 ^ b63 & b60 ^ b37 & b33 ^ b15 & b9 ^ b60 & b52 & b45 ^ b33 & b28 & b21 ^ b63 & b45 & b28 & b9 ^ b60 & b52 & b37 & b33 ^ b63 & b60 & b21 & b15 ^ b63 & b60 & b52 & b45 & b37 ^ b33 & b28 & b21 & b15 & b9 ^ b52 & b45 & b37 & b33 & b28 & b21) & 0x0000FFFF; }
Get output from linear function f(x).
Returns:Output from LFSR.
/** * Get output from linear function f(x). * * @return Output from LFSR. */
private int getOutputLFSR() { int s0 = lfsr[0]; int s13 = lfsr[0] >>> 13 | lfsr[1] << 3; int s23 = lfsr[1] >>> 7 | lfsr[2] << 9; int s38 = lfsr[2] >>> 6 | lfsr[3] << 10; int s51 = lfsr[3] >>> 3 | lfsr[4] << 13; int s62 = lfsr[3] >>> 14 | lfsr[4] << 2; return (s0 ^ s13 ^ s23 ^ s38 ^ s51 ^ s62) & 0x0000FFFF; }
Get output from output function h(x).
Returns:Output from h(x).
/** * Get output from output function h(x). * * @return Output from h(x). */
private int getOutput() { int b1 = nfsr[0] >>> 1 | nfsr[1] << 15; int b2 = nfsr[0] >>> 2 | nfsr[1] << 14; int b4 = nfsr[0] >>> 4 | nfsr[1] << 12; int b10 = nfsr[0] >>> 10 | nfsr[1] << 6; int b31 = nfsr[1] >>> 15 | nfsr[2] << 1; int b43 = nfsr[2] >>> 11 | nfsr[3] << 5; int b56 = nfsr[3] >>> 8 | nfsr[4] << 8; int b63 = nfsr[3] >>> 15 | nfsr[4] << 1; int s3 = lfsr[0] >>> 3 | lfsr[1] << 13; int s25 = lfsr[1] >>> 9 | lfsr[2] << 7; int s46 = lfsr[2] >>> 14 | lfsr[3] << 2; int s64 = lfsr[4]; return (s25 ^ b63 ^ s3 & s64 ^ s46 & s64 ^ s64 & b63 ^ s3 & s25 & s46 ^ s3 & s46 & s64 ^ s3 & s46 & b63 ^ s25 & s46 & b63 ^ s46 & s64 & b63 ^ b1 ^ b2 ^ b4 ^ b10 ^ b31 ^ b43 ^ b56) & 0x0000FFFF; }
Shift array 16 bits and add val to index.length - 1.
Params:
  • array – The array to shift.
  • val – The value to shift in.
Returns:The shifted array with val added to index.length - 1.
/** * Shift array 16 bits and add val to index.length - 1. * * @param array The array to shift. * @param val The value to shift in. * @return The shifted array with val added to index.length - 1. */
private int[] shift(int[] array, int val) { array[0] = array[1]; array[1] = array[2]; array[2] = array[3]; array[3] = array[4]; array[4] = val; return array; }
Set keys, reset cipher.
Params:
  • keyBytes – The key.
  • ivBytes – The IV.
/** * Set keys, reset cipher. * * @param keyBytes The key. * @param ivBytes The IV. */
private void setKey(byte[] keyBytes, byte[] ivBytes) { ivBytes[8] = (byte)0xFF; ivBytes[9] = (byte)0xFF; workingKey = keyBytes; workingIV = ivBytes; /** * Load NFSR and LFSR */ int j = 0; for (int i = 0; i < nfsr.length; i++) { nfsr[i] = (workingKey[j + 1] << 8 | workingKey[j] & 0xFF) & 0x0000FFFF; lfsr[i] = (workingIV[j + 1] << 8 | workingIV[j] & 0xFF) & 0x0000FFFF; j += 2; } } public void processBytes(byte[] in, int inOff, int len, byte[] out, int outOff) throws DataLengthException { if (!initialised) { throw new IllegalStateException(getAlgorithmName() + " not initialised"); } if ((inOff + len) > in.length) { throw new DataLengthException("input buffer too short"); } if ((outOff + len) > out.length) { throw new DataLengthException("output buffer too short"); } for (int i = 0; i < len; i++) { out[outOff + i] = (byte)(in[inOff + i] ^ getKeyStream()); } } public void reset() { index = 2; setKey(workingKey, workingIV); initGrain(); }
Run Grain one round(i.e. 16 bits).
/** * Run Grain one round(i.e. 16 bits). */
private void oneRound() { output = getOutput(); out[0] = (byte)output; out[1] = (byte)(output >> 8); nfsr = shift(nfsr, getOutputNFSR() ^ lfsr[0]); lfsr = shift(lfsr, getOutputLFSR()); } public byte returnByte(byte in) { if (!initialised) { throw new IllegalStateException(getAlgorithmName() + " not initialised"); } return (byte)(in ^ getKeyStream()); } private byte getKeyStream() { if (index > 1) { oneRound(); index = 0; } return out[index++]; } }