internal static Tweak EncodeTweak(UInt64 position, bool bitPad, TweakType type, bool first, bool final)
{
//
// Takes tweak parameters and encodes them in a 128 bit value. The lower half of the 128 byte value (only the position)
// is stuck in low64 and the high half in stuck in high64.
//
// N.B SimpleSkeinManaged specifies that position can be upto 2^96 but we support only 2^64. We could add support by rolling our own BigInteger
//
// The encoding is as follows (ASCII art not to scale)
//
// 128 120 112 96 0
// --------------------------------------------------------------------------------------------
// F1|F2| Type |B| TreeLevel | reserved | Position |
// | | | | | | |
// --------------------------------------------------------------------------------------------
// F1 = First
// F2 = Final
// B - BitPad
//
Tweak tweak = new Tweak(0,0);
tweak.high64 = 0;
//
// The shift numbers are calculated using 64 - (128 - end-byte-from-diagram-above)
//
if (final) tweak.high64 |= (UInt64)1L << 63; // Set F1 in diagram above
if (first) tweak.high64 |= (UInt64)1L << 62; // Set F2 in diagram above
tweak.high64 |= (UInt64)type << 56; // Set type
if (bitPad) tweak.high64 |= (UInt64)1L << 55; // Set bit pad
tweak.low64 = position;
return tweak;
}
internal void Update(UInt64[] message, Tweak tweak)
{
//
// Takes encoded tweak value and message, encrypts using current state as key and XORs
// result with message. The block size is determined by looking at input message length
// TODO: Reuse block cipher instance
//
if (_Hi.Length != message.Length){
throw new InvalidOperationException("Can't change block size in mid flight");
}
Threefish threeFish = new Threefish(_Hi, tweak, _blockSize);
threeFish.Encrypt(message, _Hi);
for (int i = 0; i < _Hi.Length; i++){
_Hi[i] ^= message[i];
}
}
public Threefish(UInt64[] key, Tweak tweak, ThreeFishBlockSize blockSize)
{
//
// TODO: Move non-onetime initialization so that consumers can cache instances
//
if (key.Length != (int)blockSize/8) {
throw new ArgumentException("Key size should match block size");
}
this.BlockSize = blockSize;
//
// Set number of words rounds based on block size
//
_numWords = (int)BlockSize / sizeof(UInt64);
switch (BlockSize) {
case ThreeFishBlockSize.BLOCKSIZE_256_BITS:
this._rounds = ThreeFishRounds.ROUNDS_72;
this.RotationConstants = Rdj_Nw_4;
this.PermutationPi = Threefish.PI_I_Nw_4;
break;
case ThreeFishBlockSize.BLOCKSIZE_512_BITS:
this._rounds = ThreeFishRounds.ROUNDS_72;
this.RotationConstants = Rdj_Nw_8;
this.PermutationPi = Threefish.PI_I_Nw_8;
break;
case ThreeFishBlockSize.BLOCKSIZE_1024_BITS:
this._rounds = ThreeFishRounds.ROUNDS_80;
this.RotationConstants = Rdj_Nw_16;
this.PermutationPi = Threefish.PI_I_Nw_16;
break;
}
//
// KeyWords is special in that it has an extra element kNw at the end
//
this.KeyWords = new UInt64[key.Length + 1];
Array.Copy(key, KeyWords, key.Length) ;
//
// Initialize Vd, Ed, fd and Ksd
//
_vd = new UInt64[_numWords];
_ed = new UInt64[_numWords];
_kdi = new UInt64[_numWords];
_fd = new UInt64[_numWords];
//
// Initialize ts values(as per section 3.3.2)
//
_ts[0] = tweak.low64;
_ts[1] = tweak.high64;
_ts[2] = _ts[0] ^ _ts[1];
//
// Initialize kNw (as per section 3.3.2). Already set to 2^64/3
//
for (int i = 0; i < _numWords; i++) {
_kNw ^= KeyWords[i];
}
KeyWords[_numWords] = _kNw;
}
