package org.bouncycastle.crypto.engines;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.MaxBytesExceededException;
import org.bouncycastle.crypto.OutputLengthException;
import org.bouncycastle.crypto.StreamCipher;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;
import org.bouncycastle.crypto.util.Pack;
import org.bouncycastle.util.Strings;
/**
* Implementation of Daniel J. Bernstein's Salsa20 stream cipher, Snuffle 2005
*/
public class Salsa20Engine
implements StreamCipher
{
public final static int DEFAULT_ROUNDS = 20;
/** Constants */
private final static int STATE_SIZE = 16; // 16, 32 bit ints = 64 bytes
protected final static byte[]
sigma = Strings.toByteArray("expand 32-byte k"),
tau = Strings.toByteArray("expand 16-byte k");
protected int rounds;
/*
* variables to hold the state of the engine
* during encryption and decryption
*/
private int index = 0;
protected int[] engineState = new int[STATE_SIZE]; // state
protected int[] x = new int[STATE_SIZE] ; // internal buffer
private byte[] keyStream = new byte[STATE_SIZE * 4]; // expanded state, 64 bytes
private boolean initialised = false;
/*
* internal counter
*/
private int cW0, cW1, cW2;
/**
* Creates a 20 round Salsa20 engine.
*/
public Salsa20Engine()
{
this(DEFAULT_ROUNDS);
}
/**
* Creates a Salsa20 engine with a specific number of rounds.
* @param rounds the number of rounds (must be an even number).
*/
public Salsa20Engine(int rounds)
{
if (rounds <= 0 || (rounds & 1) != 0)
{
throw new IllegalArgumentException("'rounds' must be a positive, even number");
}
this.rounds = rounds;
}
/**
* 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(getAlgorithmName() + " Init parameters must include an IV");
}
ParametersWithIV ivParams = (ParametersWithIV) params;
byte[] iv = ivParams.getIV();
if (iv == null || iv.length != getNonceSize())
{
throw new IllegalArgumentException(getAlgorithmName() + " requires exactly " + getNonceSize()
+ " bytes of IV");
}
if (!(ivParams.getParameters() instanceof KeyParameter))
{
throw new IllegalArgumentException(getAlgorithmName() + " Init parameters must include a key");
}
KeyParameter key = (KeyParameter) ivParams.getParameters();
setKey(key.getKey(), iv);
reset();
initialised = true;
}
protected int getNonceSize()
{
return 8;
}
public String getAlgorithmName()
{
String name = "Salsa20";
if (rounds != DEFAULT_ROUNDS)
{
name += "/" + rounds;
}
return name;
}
public byte returnByte(byte in)
{
if (limitExceeded())
{
throw new MaxBytesExceededException("2^70 byte limit per IV; Change IV");
}
if (index == 0)
{
generateKeyStream(keyStream);
advanceCounter();
}
byte out = (byte)(keyStream[index]^in);
index = (index + 1) & 63;
return out;
}
protected void advanceCounter()
{
if (++engineState[8] == 0)
{
++engineState[9];
}
}
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 OutputLengthException("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)
{
generateKeyStream(keyStream);
advanceCounter();
}
out[i+outOff] = (byte)(keyStream[index]^in[i+inOff]);
index = (index + 1) & 63;
}
}
public void reset()
{
index = 0;
resetLimitCounter();
resetCounter();
}
protected void resetCounter()
{
engineState[8] = engineState[9] = 0;
}
protected void setKey(byte[] keyBytes, byte[] ivBytes)
{
if ((keyBytes.length != 16) && (keyBytes.length != 32)) {
throw new IllegalArgumentException(getAlgorithmName() + " requires 128 bit or 256 bit key");
}
int offset = 0;
byte[] constants;
// Key
engineState[1] = Pack.littleEndianToInt(keyBytes, 0);
engineState[2] = Pack.littleEndianToInt(keyBytes, 4);
engineState[3] = Pack.littleEndianToInt(keyBytes, 8);
engineState[4] = Pack.littleEndianToInt(keyBytes, 12);
if (keyBytes.length == 32)
{
constants = sigma;
offset = 16;
}
else
{
constants = tau;
}
engineState[11] = Pack.littleEndianToInt(keyBytes, offset);
engineState[12] = Pack.littleEndianToInt(keyBytes, offset+4);
engineState[13] = Pack.littleEndianToInt(keyBytes, offset+8);
engineState[14] = Pack.littleEndianToInt(keyBytes, offset+12);
engineState[0 ] = Pack.littleEndianToInt(constants, 0);
engineState[5 ] = Pack.littleEndianToInt(constants, 4);
engineState[10] = Pack.littleEndianToInt(constants, 8);
engineState[15] = Pack.littleEndianToInt(constants, 12);
// IV
engineState[6] = Pack.littleEndianToInt(ivBytes, 0);
engineState[7] = Pack.littleEndianToInt(ivBytes, 4);
resetCounter();
}
protected void generateKeyStream(byte[] output)
{
salsaCore(rounds, engineState, x);
Pack.intToLittleEndian(x, output, 0);
}
/**
* Salsa20 function
*
* @param input input data
*
* @return keystream
*/
public static void salsaCore(int rounds, int[] input, int[] x)
{
if (input.length != 16) {
throw new IllegalArgumentException();
}
if (x.length != 16) {
throw new IllegalArgumentException();
}
if (rounds % 2 != 0) {
throw new IllegalArgumentException("Number of rounds must be even");
}
int x00 = input[ 0];
int x01 = input[ 1];
int x02 = input[ 2];
int x03 = input[ 3];
int x04 = input[ 4];
int x05 = input[ 5];
int x06 = input[ 6];
int x07 = input[ 7];
int x08 = input[ 8];
int x09 = input[ 9];
int x10 = input[10];
int x11 = input[11];
int x12 = input[12];
int x13 = input[13];
int x14 = input[14];
int x15 = input[15];
for (int i = rounds; i > 0; i -= 2)
{
x04 ^= rotl((x00+x12), 7);
x08 ^= rotl((x04+x00), 9);
x12 ^= rotl((x08+x04),13);
x00 ^= rotl((x12+x08),18);
x09 ^= rotl((x05+x01), 7);
x13 ^= rotl((x09+x05), 9);
x01 ^= rotl((x13+x09),13);
x05 ^= rotl((x01+x13),18);
x14 ^= rotl((x10+x06), 7);
x02 ^= rotl((x14+x10), 9);
x06 ^= rotl((x02+x14),13);
x10 ^= rotl((x06+x02),18);
x03 ^= rotl((x15+x11), 7);
x07 ^= rotl((x03+x15), 9);
x11 ^= rotl((x07+x03),13);
x15 ^= rotl((x11+x07),18);
x01 ^= rotl((x00+x03), 7);
x02 ^= rotl((x01+x00), 9);
x03 ^= rotl((x02+x01),13);
x00 ^= rotl((x03+x02),18);
x06 ^= rotl((x05+x04), 7);
x07 ^= rotl((x06+x05), 9);
x04 ^= rotl((x07+x06),13);
x05 ^= rotl((x04+x07),18);
x11 ^= rotl((x10+x09), 7);
x08 ^= rotl((x11+x10), 9);
x09 ^= rotl((x08+x11),13);
x10 ^= rotl((x09+x08),18);
x12 ^= rotl((x15+x14), 7);
x13 ^= rotl((x12+x15), 9);
x14 ^= rotl((x13+x12),13);
x15 ^= rotl((x14+x13),18);
}
x[ 0] = x00 + input[ 0];
x[ 1] = x01 + input[ 1];
x[ 2] = x02 + input[ 2];
x[ 3] = x03 + input[ 3];
x[ 4] = x04 + input[ 4];
x[ 5] = x05 + input[ 5];
x[ 6] = x06 + input[ 6];
x[ 7] = x07 + input[ 7];
x[ 8] = x08 + input[ 8];
x[ 9] = x09 + input[ 9];
x[10] = x10 + input[10];
x[11] = x11 + input[11];
x[12] = x12 + input[12];
x[13] = x13 + input[13];
x[14] = x14 + input[14];
x[15] = x15 + input[15];
}
/**
* Rotate left
*
* @param x value to rotate
* @param y amount to rotate x
*
* @return rotated x
*/
protected static int rotl(int x, int y)
{
return (x << y) | (x >>> -y);
}
private void resetLimitCounter()
{
cW0 = 0;
cW1 = 0;
cW2 = 0;
}
private boolean limitExceeded()
{
if (++cW0 == 0)
{
if (++cW1 == 0)
{
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)
{
cW0 += len;
if (cW0 < len && cW0 >= 0)
{
if (++cW1 == 0)
{
return (++cW2 & 0x20) != 0; // 2^(32 + 32 + 6)
}
}
return false;
}
}