AESEncryption.cs

//AES Encryption
public static string EncryptString(string plainText, string keyToUse) {
  byte[] iv = new byte[16];
  byte[] array;

  using(Aes aes = Aes.Create()) {
    aes.Key = Encoding.UTF8.GetBytes(Get128BitString(keyToUse));
    aes.IV = iv;

    ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

    using(MemoryStream memoryStream = new MemoryStream()) {
      using(CryptoStream cryptoStream = new CryptoStream((Stream) memoryStream, encryptor, CryptoStreamMode.Write)) {
        using(StreamWriter streamWriter = new StreamWriter((Stream) cryptoStream)) {
          streamWriter.Write(plainText);
        }

        array = memoryStream.ToArray();
      }
    }
  }

  return Convert.ToBase64String(array);
}

public static string DecryptString(string cipherText, string keyToUse) {
  byte[] iv = new byte[16];
  byte[] buffer = Convert.FromBase64String(cipherText);

  using(Aes aes = Aes.Create()) {
    aes.Key = Encoding.UTF8.GetBytes(Get128BitString(keyToUse));
    aes.IV = iv;
    ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);

    using(MemoryStream memoryStream = new MemoryStream(buffer)) {
      using(CryptoStream cryptoStream = new CryptoStream((Stream) memoryStream, decryptor, CryptoStreamMode.Read)) {
        using(StreamReader streamReader = new StreamReader((Stream) cryptoStream)) {
          return streamReader.ReadToEnd();
        }
      }
    }
  }
}

public static string Get128BitString(string keyToConvert) {
  StringBuilder b = new StringBuilder();
  for (int i = 0; i < 16; i++) {
    b.Append(keyToConvert[i % keyToConvert.Length]);
  }
  keyToConvert = b.ToString();

  return keyToConvert;
}
}