private BitArray F(BitArray bitArray, BitArray key)
{
if (bitArray.Count != 4)
{
throw new ArgumentException("F argument length should be 4 bits");
}
var permuteAndExpand = new BitArray(8)
{
[0] = bitArray[3],
[1] = bitArray[0],
[2] = bitArray[1],
[3] = bitArray[2],
[4] = bitArray[1],
[5] = bitArray[2],
[6] = bitArray[3],
[7] = bitArray[0]
};
var xoredWithKey = permuteAndExpand.NormalXor(key);
var leftPart = SimplifiedDesHelper.GetLeftPart(xoredWithKey);
var rightPart = SimplifiedDesHelper.GetRightPart(xoredWithKey);
var leftPartSboxed = Sbox(leftPart, 1);
var rightPartSboxed = Sbox(rightPart, 2);
return(SimplifiedDesHelper.P4(leftPartSboxed.Merge(rightPartSboxed)));
}
private BitArray Switch(BitArray bitArray)
{
var leftPart = SimplifiedDesHelper.GetLeftPart(bitArray);
var rightPart = SimplifiedDesHelper.GetRightPart(bitArray);
return(rightPart.Merge(leftPart));
}
private BitArray Fk(BitArray afterIp, BitArray key)
{
var left = SimplifiedDesHelper.GetLeftPart(afterIp);
var right = SimplifiedDesHelper.GetRightPart(afterIp);
left = left.NormalXor(F(right, key));
return(left.Merge(right));
}