package org.bouncycastle.crypto.engines;

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

Implementation of Daniel J. Bernstein's Salsa20 stream cipher, Snuffle 2005
/** * Implementation of Daniel J. Bernstein's Salsa20 stream cipher, Snuffle 2005 */
public class Salsa20Engine implements StreamCipher {
Constants
/** Constants */
private final static int stateSize = 16; // 16, 32 bit ints = 64 bytes private final static byte[] sigma = Strings.toByteArray("expand 32-byte k"), tau = Strings.toByteArray("expand 16-byte k"); /* * variables to hold the state of the engine * during encryption and decryption */ private int index = 0; private int[] engineState = new int[stateSize]; // state private int[] x = new int[stateSize] ; // internal buffer private byte[] keyStream = new byte[stateSize * 4], // expanded state, 64 bytes workingKey = null, workingIV = null; private boolean initialised = false; /* * internal counter */ private int cW0, cW1, cW2;
initialise a Salsa20 cipher.
Params:
  • forEncryption – whether or not we are for encryption.
  • params – the parameters required to set up the cipher.
Throws:
/** * initialise a Salsa20 cipher. * * @param forEncryption whether or not we are for encryption. * @param params the parameters required to set up the cipher. * @exception IllegalArgumentException if the params argument is * inappropriate. */
public void init( boolean forEncryption, CipherParameters params) { /* * Salsa20 encryption and decryption is completely * symmetrical, so the 'forEncryption' is * irrelevant. (Like 90% of stream ciphers) */ if (!(params instanceof ParametersWithIV)) { throw new IllegalArgumentException("Salsa20 Init parameters must include an IV"); } ParametersWithIV ivParams = (ParametersWithIV) params; byte[] iv = ivParams.getIV(); if (iv == null || iv.length != 8) { throw new IllegalArgumentException("Salsa20 requires exactly 8 bytes of IV"); } if (!(ivParams.getParameters() instanceof KeyParameter)) { throw new IllegalArgumentException("Salsa20 Init parameters must include a key"); } KeyParameter key = (KeyParameter) ivParams.getParameters(); workingKey = key.getKey(); workingIV = iv; setKey(workingKey, workingIV); } public String getAlgorithmName() { return "Salsa20"; } public byte returnByte(byte in) { if (limitExceeded()) { throw new MaxBytesExceededException("2^70 byte limit per IV; Change IV"); } if (index == 0) { salsa20WordToByte(engineState, keyStream); engineState[8]++; if (engineState[8] == 0) { engineState[9]++; } } byte out = (byte)(keyStream[index]^in); index = (index + 1) & 63; return out; } public void processBytes( byte[] in, int inOff, int len, byte[] out, int outOff) { 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"); } if (limitExceeded(len)) { throw new MaxBytesExceededException("2^70 byte limit per IV would be exceeded; Change IV"); } for (int i = 0; i < len; i++) { if (index == 0) { salsa20WordToByte(engineState, keyStream); engineState[8]++; if (engineState[8] == 0) { engineState[9]++; } } out[i+outOff] = (byte)(keyStream[index]^in[i+inOff]); index = (index + 1) & 63; } } public void reset() { setKey(workingKey, workingIV); } // Private implementation private void setKey(byte[] keyBytes, byte[] ivBytes) { workingKey = keyBytes; workingIV = ivBytes; index = 0; resetCounter(); int offset = 0; byte[] constants; // Key engineState[1] = byteToIntLittle(workingKey, 0); engineState[2] = byteToIntLittle(workingKey, 4); engineState[3] = byteToIntLittle(workingKey, 8); engineState[4] = byteToIntLittle(workingKey, 12); if (workingKey.length == 32) { constants = sigma; offset = 16; } else { constants = tau; } engineState[11] = byteToIntLittle(workingKey, offset); engineState[12] = byteToIntLittle(workingKey, offset+4); engineState[13] = byteToIntLittle(workingKey, offset+8); engineState[14] = byteToIntLittle(workingKey, offset+12); engineState[0 ] = byteToIntLittle(constants, 0); engineState[5 ] = byteToIntLittle(constants, 4); engineState[10] = byteToIntLittle(constants, 8); engineState[15] = byteToIntLittle(constants, 12); // IV engineState[6] = byteToIntLittle(workingIV, 0); engineState[7] = byteToIntLittle(workingIV, 4); engineState[8] = engineState[9] = 0; initialised = true; }
Salsa20 function
Params:
  • input – input data
Returns: keystream
/** * Salsa20 function * * @param input input data * * @return keystream */
private void salsa20WordToByte(int[] input, byte[] output) { System.arraycopy(input, 0, x, 0, input.length); for (int i = 0; i < 10; i++) { x[ 4] ^= rotl((x[ 0]+x[12]), 7); x[ 8] ^= rotl((x[ 4]+x[ 0]), 9); x[12] ^= rotl((x[ 8]+x[ 4]),13); x[ 0] ^= rotl((x[12]+x[ 8]),18); x[ 9] ^= rotl((x[ 5]+x[ 1]), 7); x[13] ^= rotl((x[ 9]+x[ 5]), 9); x[ 1] ^= rotl((x[13]+x[ 9]),13); x[ 5] ^= rotl((x[ 1]+x[13]),18); x[14] ^= rotl((x[10]+x[ 6]), 7); x[ 2] ^= rotl((x[14]+x[10]), 9); x[ 6] ^= rotl((x[ 2]+x[14]),13); x[10] ^= rotl((x[ 6]+x[ 2]),18); x[ 3] ^= rotl((x[15]+x[11]), 7); x[ 7] ^= rotl((x[ 3]+x[15]), 9); x[11] ^= rotl((x[ 7]+x[ 3]),13); x[15] ^= rotl((x[11]+x[ 7]),18); x[ 1] ^= rotl((x[ 0]+x[ 3]), 7); x[ 2] ^= rotl((x[ 1]+x[ 0]), 9); x[ 3] ^= rotl((x[ 2]+x[ 1]),13); x[ 0] ^= rotl((x[ 3]+x[ 2]),18); x[ 6] ^= rotl((x[ 5]+x[ 4]), 7); x[ 7] ^= rotl((x[ 6]+x[ 5]), 9); x[ 4] ^= rotl((x[ 7]+x[ 6]),13); x[ 5] ^= rotl((x[ 4]+x[ 7]),18); x[11] ^= rotl((x[10]+x[ 9]), 7); x[ 8] ^= rotl((x[11]+x[10]), 9); x[ 9] ^= rotl((x[ 8]+x[11]),13); x[10] ^= rotl((x[ 9]+x[ 8]),18); x[12] ^= rotl((x[15]+x[14]), 7); x[13] ^= rotl((x[12]+x[15]), 9); x[14] ^= rotl((x[13]+x[12]),13); x[15] ^= rotl((x[14]+x[13]),18); } int offset = 0; for (int i = 0; i < stateSize; i++) { intToByteLittle(x[i] + input[i], output, offset); offset += 4; } for (int i = stateSize; i < x.length; i++) { intToByteLittle(x[i], output, offset); offset += 4; } }
32 bit word to 4 byte array in little endian order
Params:
  • x – value to 'unpack'
Returns: value of x expressed as a byte[] array in little endian order
/** * 32 bit word to 4 byte array in little endian order * * @param x value to 'unpack' * * @return value of x expressed as a byte[] array in little endian order */
private byte[] intToByteLittle(int x, byte[] out, int off) { out[off] = (byte)x; out[off + 1] = (byte)(x >>> 8); out[off + 2] = (byte)(x >>> 16); out[off + 3] = (byte)(x >>> 24); return out; }
Rotate left
Params:
  • x – value to rotate
  • y – amount to rotate x
Returns: rotated x
/** * Rotate left * * @param x value to rotate * @param y amount to rotate x * * @return rotated x */
private int rotl(int x, int y) { return (x << y) | (x >>> -y); }
Pack byte[] array into an int in little endian order
Params:
  • x – byte array to 'pack'
  • offset – only x[offset]..x[offset+3] will be packed
Returns: x[offset]..x[offset+3] 'packed' into an int in little-endian order
/** * Pack byte[] array into an int in little endian order * * @param x byte array to 'pack' * @param offset only x[offset]..x[offset+3] will be packed * * @return x[offset]..x[offset+3] 'packed' into an int in little-endian order */
private int byteToIntLittle(byte[] x, int offset) { return ((x[offset] & 255)) | ((x[offset + 1] & 255) << 8) | ((x[offset + 2] & 255) << 16) | (x[offset + 3] << 24); } private void resetCounter() { cW0 = 0; cW1 = 0; cW2 = 0; } private boolean limitExceeded() { cW0++; if (cW0 == 0) { cW1++; if (cW1 == 0) { cW2++; return (cW2 & 0x20) != 0; // 2^(32 + 32 + 6) } } return false; } /* * this relies on the fact len will always be positive. */ private boolean limitExceeded(int len) { if (cW0 >= 0) { cW0 += len; } else { cW0 += len; if (cW0 >= 0) { cW1++; if (cW1 == 0) { cW2++; return (cW2 & 0x20) != 0; // 2^(32 + 32 + 6) } } } return false; } }