public static string DecryptVi(string ciphertext, string key)
{
char letter;
string plaintext = "";
int j = 0;
key = key.ToLower();
letter = ' ';
for (int i = 0; i < ciphertext.Length; i++, j++)//i for the ciphertext and j for the key
{
if (j == key.Length)
{
j = 0;
}//check the key back to the start if needed
char character = ciphertext[i];
char keyLetter = key[j];
int shift = Convert.ToInt32(keyLetter) - 97;
letter = Convert.ToChar(CeaserCipher.DecryptCC(character.ToString(), shift));//ceaser shift the characters back
plaintext += letter;
}
return(plaintext);
}
public static string EncryptVi(string plaintext, string key)
{
char letter;//declare and intitialise variables
string ciphertext = "";
int j = 0;
key = key.ToLower();
letter = ' ';
for (int i = 0; i < plaintext.Length; i++, j++)//j is for the key, i is for the plaintext
{
if (j == key.Length)
{
j = 0;
}//loop for checking if the key needs resetting
char character = plaintext[i];
char keyLetter = key[j];
int shift = Convert.ToInt32(keyLetter) - 97;
letter = Convert.ToChar(CeaserCipher.EncryptCC(character.ToString(), shift)); //ceaser cipher the induvidual characters by the shift of one of the key characters
ciphertext += letter; //add to the ciphertext
}
return(ciphertext);
}