using System;
using System.Text;
using Org.BouncyCastle.Crypto.Parameters;
namespace Org.BouncyCastle.Crypto.Engines{
/**
* Implementation of Daniel J. Bernstein's Salsa20 stream cipher, Snuffle 2005
*/
public class Salsa20Engine
: IStreamCipher
{
/** Constants */
private const int stateSize = 16; // 16, 32 bit ints = 64 bytes
private readonly static byte[]
sigma = Encoding.ASCII.GetBytes("expand 32-byte k"),
tau = Encoding.ASCII.GetBytes("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 bool 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 ArgumentException if the params argument is
* inappropriate.
*/
public void Init(
bool forEncryption,
ICipherParameters parameters)
{
/*
* Salsa20 encryption and decryption is completely
* symmetrical, so the 'forEncryption' is
* irrelevant. (Like 90% of stream ciphers)
*/
ParametersWithIV ivParams = parameters as ParametersWithIV;
if (ivParams == null)
throw new ArgumentException("Salsa20 Init requires an IV", "parameters");
byte[] iv = ivParams.GetIV();
if (iv == null || iv.Length != 8)
throw new ArgumentException("Salsa20 requires exactly 8 bytes of IV");
KeyParameter key = ivParams.Parameters as KeyParameter;
if (key == null)
throw new ArgumentException("Salsa20 Init requires a key", "parameters");
workingKey = key.GetKey();
workingIV = iv;
setKey(workingKey, workingIV);
}
public string AlgorithmName
{
get { return "Salsa20"; }
}
public byte ReturnByte(
byte input)
{
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 output = (byte)(keyStream[index]^input);
index = (index + 1) & 63;
return output;
}
public void ProcessBytes(
byte[] inBytes,
int inOff,
int len,
byte[] outBytes,
int outOff)
{
if (!initialised)
{
throw new InvalidOperationException(AlgorithmName + " not initialised");
}
if ((inOff + len) > inBytes.Length)
{
throw new DataLengthException("input buffer too short");
}
if ((outOff + len) > outBytes.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]++;
}
}
outBytes[i+outOff] = (byte)(keyStream[index]^inBytes[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
*
* @param input input data
*
* @return keystream
*/
private void salsa20WordToByte(
int[] input,
byte[] output)
{
Array.Copy(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
*
* @param x value to 'unpack'
*
* @return value of x expressed as a byte[] array in little endian order
*/
private byte[] intToByteLittle(
int x,
byte[] bs,
int off)
{
bs[off] = (byte)x;
bs[off + 1] = (byte)(x >> 8);
bs[off + 2] = (byte)(x >> 16);
bs[off + 3] = (byte)(x >> 24);
return bs;
}
/**
* 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) | ((int)((uint) x >> -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 + 1] & 255) << 8) |
((x[offset + 2] & 255) << 16) |
(x[offset + 3] << 24);
}
private void resetCounter()
{
cW0 = 0;
cW1 = 0;
cW2 = 0;
}
private bool 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 bool 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;
}
}
}
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