public string DecryptMessage(string cipherText, VigenereKey cipherKey)
{
// Nothing to decrypt.
if (!DoesInputContainAlphabeticalCharacters(cipherText))
{
return(string.Empty);
}
// Valid Vigenere cipher text (at least within this implementation) will contain only upper case letters
// and special characters. Therefore any lower case letters render message invalid. Do not continue.
if (cipherText.Where(char.IsLetter).Any(char.IsLower))
{
throw new InvalidOperationException("Invalid cipher text.");
}
var sb = new StringBuilder(string.Empty);
var cipherAlphabets = GetCipherAlphabets(cipherKey.MemorableKey);
var keyIndex = 0;
foreach (var encryptedCharacter in cipherText)
{
// Append special characters.
if (!IsAlphabeticalCharacter(encryptedCharacter))
{
sb.Append(encryptedCharacter);
continue;
}
var multiAlphabetIndex = keyIndex % cipherKey.MemorableKey.Length;
var currentAlphabet = cipherAlphabets
.First(a => a.First().Equals(cipherKey.MemorableKey[multiAlphabetIndex]));
sb.Append(currentAlphabet[Alphabet.IndexOf(encryptedCharacter)]);
// Prevent keyIndex from overflowing.
keyIndex = GetUpdatedKeyIndex(keyIndex, cipherKey.MemorableKey);
}
return(sb.ToString().ToLower());
}
public string EncryptMessage(string plainText, VigenereKey cipherKey)
{
// Nothing to encrypt.
if (!DoesInputContainAlphabeticalCharacters(plainText))
{
return(string.Empty);
}
if (!DoesInputContainAlphabeticalCharacters(cipherKey.MemorableKey))
{
return(string.Empty);
}
var sb = new StringBuilder(string.Empty);
var cipherAlphabets = GetCipherAlphabets(cipherKey.MemorableKey);
var keyIndex = 0;
foreach (var plainTextCharacter in plainText.ToUpper())
{
// Append special characters
if (!IsAlphabeticalCharacter(plainTextCharacter))
{
sb.Append(plainTextCharacter);
continue;
}
var multiAlphabetIndex = keyIndex % cipherKey.MemorableKey.Length;
var currentAlphabet = cipherAlphabets
.First(a => a.First().Equals(cipherKey.MemorableKey[multiAlphabetIndex]));
sb.Append(currentAlphabet[Alphabet.IndexOf(plainTextCharacter)]);
// Prevent keyIndex from overflowing.
keyIndex = GetUpdatedKeyIndex(keyIndex, cipherKey.MemorableKey);
}
return(sb.ToString());
}
