/// <summary>
/// Key = (a,b)
/// Modulo = m
/// E(x) = (ax + b) mod m
/// </summary>
/// <param name="plaintext"></param>
/// <returns>Ciphertext</returns>
public override string Encryption(string plaintext, int start = 'A') =>
new String(plaintext.ToCharArray().Select(x => Convert.ToChar(
(((PrivateKey.ElementAt(0) * (x - start) + PrivateKey.ElementAt(1))) % Mod.Modulo)
)).ToArray());
/// <summary>
/// Key = (a,b)
/// Modulo = m
/// D(y) = Inverse(a,m) * (y - b) mod m
/// </summary>
/// <param name="ciphertext"></param>
/// <returns></returns>
public override string Decryption(string ciphertext, int start = 'A') =>
new String(ciphertext.ToCharArray().Select(y => Convert.ToChar(
(Mod.PositiveMod(Mod.Inverse(PrivateKey.ElementAt(0)) *
(y - start - PrivateKey.ElementAt(1))) + start)
)).ToArray());
/// <summary>
/// D(y) = y^a mod n
/// </summary>
/// <param name="ciphertext"></param>
/// <returns></returns>
public override string Decryption(string ciphertext, int start = 0) =>
new String(ciphertext.ToCharArray().Select(y => Convert.ToChar(
start + BigInteger.ModPow(y - start, PrivateKey.ElementAt(2), PublicKey.ElementAt(0))
)).ToArray());
