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
*/
public class Salsa20Engine
implements StreamCipher
{
/** 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 = null; // state
private byte[] keyStream = new byte[stateSize>>2], // expanded state, 64 bytes
workingKey = null,
workingIV = null;
private boolean initialised = false;
/*
* internal counter
*/
private int cW0, cW1, cW2;
/**
* 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)
{
CipherParameters keyParam = params;
if (params instanceof ParametersWithIV)
{
workingIV = ((ParametersWithIV)params).getIV();
keyParam = ((ParametersWithIV)params).getParameters();
}
if (keyParam instanceof KeyParameter)
{
/*
* Salsa20 encryption and decryption is completely
* symmetrical, so the 'forEncryption' is
* irrelevant. (Like 90% of stream ciphers)
*/
workingKey = ((KeyParameter)keyParam).getKey();
setKey(workingKey, workingIV);
return;
}
throw new IllegalArgumentException("invalid parameter passed to Salsa20 init - " + params.getClass().getName());
}
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)
{
keyStream = salsa20WordToByte(engineState);
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");
}
for (int i = 0; i < len; i++)
{
if (limitExceeded())
{
throw new MaxBytesExceededException("2^70 byte limit per IV; Change IV");
}
if (index == 0)
{
keyStream = salsa20WordToByte(engineState);
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();
if (engineState == null)
{
engineState = new int[stateSize];
}
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
*
* @param input input data
*
* @return keystream
*/
private byte[] salsa20WordToByte(int[] input)
{
int[] x = new int[input.length];
System.arraycopy(input, 0, x, 0, input.length);
int i = 0;
while (i++ < 10)
{
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);
}
for (i = 0; i < stateSize; i++)
{
x[i] += input[i];
}
return intToByteLittle(x);
}
/**
* 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 = new byte[4];
out[0] = (byte)x;
out[1] = (byte)(x >>> 8);
out[2] = (byte)(x >>> 16);
out[3] = (byte)(x >>> 24);
return out;
}
/**
* Applies intToByteLittle() over an array of ints, returning a single byte array
*
* @param x array of values to 'unpack'
*
* @return byte[] array of the values in x
*/
private byte[] intToByteLittle(int[] x)
{
byte[] out = new byte[4*x.length];
for (int i = 0, j = 0; i < x.length; i++,j+=4)
{
System.arraycopy(intToByteLittle(x[i]), 0, out, j, 4);
}
return out;
}
/**
* 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 >>> (32-y));
}
/**
* 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++] & 255) << 8) |
((x[offset++] & 255) << 16) |
(x[offset ] << 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;
}
}