private static ulong ShiftKey(ulong key, int iteration)
{
var constants = new FeistelConstants();
ulong L = key >> 28;
ulong R = key << 36 >> 28;
L = L << constants.shifts[iteration] | L >> (28 - constants.shifts[iteration]);
R = R << constants.shifts[iteration] | R >> (28 - constants.shifts[iteration]);
key = L << 28 | R;
key = Permutate(key, false, constants.roundKeyIndexes);
return(key);
}
private static ulong Shrink(ulong block)
{
var constants = new FeistelConstants();
ulong result = 0;
result |= constants.SBox1[block << 58 >> 58];
result |= constants.SBox2[block << 52 >> 58] << 4;
result |= constants.SBox3[block << 46 >> 58] << 8;
result |= constants.SBox4[block << 40 >> 58] << 12;
result |= constants.SBox5[block << 34 >> 58] << 16;
result |= constants.SBox6[block << 28 >> 58] << 20;
result |= constants.SBox7[block << 22 >> 58] << 24;
result |= constants.SBox8[block << 16 >> 58] << 28;
return(result);
}
public static byte[] Decrypt(byte[] _message, byte[] _key)
{
var constants = new FeistelConstants();
ulong key = BitConverter.ToUInt64(_key, 0);
ulong[] binary = ToBinary(_message);
key = Permutate(key, false, constants.keyIndexes);
for (int j = 0; j < binary.Length; j++)
{
binary[j] = Permutate(binary[j], false, IPIndexes);
for (int i = 15; i >= 0; i--)
{
binary[j] = Round(binary[j], key, i);
}
binary[j] = (binary[j] << 32 >> 32) << 32 | (binary[j] >> 32);
binary[j] = Permutate(binary[j], true, IPIndexes);
}
return(ToBytes(binary));
}
private static ulong Round(ulong block, ulong key, int iteration)
{
var constants = new FeistelConstants();
ulong L = block >> 32;
ulong R = block << 32 >> 32;
key = ShiftKey(key, iteration);
ulong extendedR = Extend(R);
extendedR = extendedR ^ key;
ulong newR = Shrink(extendedR);
newR = Permutate(newR, false, constants.roundIndexes);
ulong result = R << 32;
result |= newR ^ L;
return(result);
}