public string Encrypt(string plainText, string key)
{
// construct the arr[5][5] based on PlayFair algorithm.
construct_array(key);
char current, next = ' ';
// this is the String that will contains the encrpted text.
String ret = "";
for (int k = 0; k < plainText.Length; k += 2)
{
current = plainText[k];
if (k < plainText.Length - 1)
{
// if there's 2 same adjacent characters seperate them by adding char 'x' in the middle.
if (plainText[k + 1] == plainText[k])
{
next = 'x';
k--;
}
else
{
next = plainText[k + 1];
}
}
// if plainText.Length is odd so the last character with paired with char 'x'
if (k + 1 == plainText.Length)
{
next = 'x';
k--;
}
// the next 2 character positions in arr[5][5]
point x1 = find(current);
point x2 = find(next);
// here's the 3 conditions of PlayFair algorithm
if (x1.getJ() == x2.getJ())
{
ret += arr[(x1.getI() + 1) % 5, x1.getJ() % 5];
ret += arr[(x2.getI() + 1) % 5, x2.getJ() % 5];
}
else if (x1.getI() == x2.getI())
{
ret += arr[(x1.getI()), (x1.getJ() + 1) % 5];
ret += arr[x2.getI(), (x2.getJ() + 1) % 5];
}
else
{
ret += arr[x1.getI(), x2.getJ()];
ret += arr[x2.getI(), x1.getJ()];
}
}
return(ret.ToUpper());
}
public string Decrypt(string cipherText, string key)
{
construct_array(key);
char current, next = ' ';
String ret = "";
for (int k = 0; k < cipherText.Length; k += 2)
{
current = Char.ToLower(cipherText[k]);
if (k < cipherText.Length - 1)
{
if (cipherText[k + 1] == cipherText[k])
{
next = 'x';
k--;
}
else
{
next = cipherText[k + 1];
}
}
if (k + 1 == cipherText.Length)
{
next = 'x';
k--;
}
point x1 = find(Char.ToLower(current));
point x2 = find(Char.ToLower(next));
if (x1.getJ() == x2.getJ())
{
if (x1.getI() == 0)
{
ret += arr[4, x1.getJ()];
}
else
{
ret += arr[x1.getI() - 1, x1.getJ()];
}
if (x2.getI() == 0)
{
ret += arr[4, x2.getJ()];
}
else
{
ret += arr[(x2.getI() - 1), x2.getJ()];
}
}
else if (x1.getI() == x2.getI())
{
if (x1.getJ() == 0)
{
ret += arr[x1.getI(), 4];
}
else
{
if (arr[(x1.getI()), (x1.getJ() - 1)] != 'x')
{
ret += arr[(x1.getI()), (x1.getJ() - 1)];
}
}
if (x2.getJ() == 0)
{
ret += arr[x2.getI(), 4];
}
else
{
ret += arr[x2.getI(), (x2.getJ() - 1)];
}
}
else
{
if (arr[x2.getI(), x1.getJ()] == 'x')
{
ret += arr[x1.getI(), x2.getJ()];
// ret += 'x';
continue;
}
// if (arr[x1.getI(), x2.getJ()] != 'x')
ret += arr[x1.getI(), x2.getJ()];
if (arr[x2.getI(), x1.getJ()] != 'x')
{
ret += arr[x2.getI(), x1.getJ()];
}
}
}
return(ret.ToUpper());
}