/*
* Transforms a pair of characters based on the rules of the playfair cipher.
* The direction argument represents wether the pair is being encrypted or decrypted.
*/
private StringBuilder TransformCharacterPair(char x, char y, int direction)
{
StringBuilder sb = new StringBuilder();
int xColumnValue = MyPolybiusSquare.GetColumnValueOf(x),
xLineValue = MyPolybiusSquare.GetLineValueOf(x),
yColumnValue = MyPolybiusSquare.GetColumnValueOf(y),
yLineValue = MyPolybiusSquare.GetLineValueOf(y);
if (xColumnValue == yColumnValue)
{
int xEncryptedVal = WrapLineValue(xLineValue + direction, direction) * 10 + xColumnValue;
int yEncryptedVal = WrapLineValue(yLineValue + direction, direction) * 10 + yColumnValue;
sb.Append(MyPolybiusSquare.GetElementOfValue(xEncryptedVal));
sb.Append(MyPolybiusSquare.GetElementOfValue(yEncryptedVal));
}
else if (xLineValue == yLineValue)
{
int xEncryptedVal = xLineValue * 10 + WrapColumnValue(xColumnValue + direction, direction);
int yEncryptedVal = yLineValue * 10 + WrapColumnValue(yColumnValue + direction, direction);
sb.Append(MyPolybiusSquare.GetElementOfValue(xEncryptedVal));
sb.Append(MyPolybiusSquare.GetElementOfValue(yEncryptedVal));
}
else
{
int xEncryptedVal = yLineValue * 10 + xColumnValue;
int yEncryptedVal = xLineValue * 10 + yColumnValue;
sb.Append(MyPolybiusSquare.GetElementOfValue(xEncryptedVal));
sb.Append(MyPolybiusSquare.GetElementOfValue(yEncryptedVal));
}
return(sb);
}
public override String Encrypt(String text)
{
StringBuilder sb = new StringBuilder(),
firstHalf = new StringBuilder(),
secondHalf = new StringBuilder();
for (int i = 0; i < text.Length; i++)
{
firstHalf.Append(MyPolybiusSquare.GetLineValueOf(text[i]));
secondHalf.Append(MyPolybiusSquare.GetColumnValueOf(text[i]));
}
String polybiusNumbers = firstHalf.Append(secondHalf).ToString();
for (int i = 0; i < polybiusNumbers.Length / 2; i++)
{
int.TryParse(polybiusNumbers.Substring(i * 2, 2), out int value);
sb.Append(MyPolybiusSquare.GetElementOfValue(value));
}
return(sb.ToString());
}
/*
* It splits the text into 2 digit numbers, and from each one the value of the current encryption character will be deducted.
*/
public override String Decrypt(String text)
{
StringBuilder sb = new StringBuilder();
String[] numbers = text.Split(' ');
int progress = 0;
for (int i = 0; i < numbers.Length; i++)
{
int.TryParse(numbers[i], out int currentNumber);
char currentEncryptionKeyChar = Key.StringValue[progress % Key.StringValue.Length];
sb.Append(MyPolybiusSquare.GetElementOfValue(currentNumber - MyPolybiusSquare.GetValueOf(currentEncryptionKeyChar)));
progress++;
}
return(sb.ToString());
}