cipher decipher sample

cipher.cs

public string Cipher(string RawData, int Key)
{
    StringBuilder CipheredText = new StringBuilder();

    byte[] RawBytes = UnicodeEncoding.UTF8.GetBytes(RawData);

    int keyLen = Key.ToString().Length;
    int keyPos = 0;

    foreach (byte rawByte in RawBytes)
    {
        keyPos = keyPos == keyLen ? 0 : keyPos;
        int cipheredByte = rawByte + int.Parse(Key.ToString()[keyPos++].ToString());
        CipheredText.Append(cipheredByte.ToString());
        CipheredText.Append("-");
    }
    return CipheredText.ToString(); //ciphered value
}

public string DeCipher(string EncryptedData, int Key)
{
    char[] seperator = {
          '-'
         };
    string[] splitted = EncryptedData.Split(seperator, StringSplitOptions.RemoveEmptyEntries);

    List<byte> BYTES = new List<byte>();

    int keyLen = Key.ToString().Length;
    int keyPos = 0;

    foreach (string s in splitted)
    {
        keyPos = keyPos == keyLen ? 0 : keyPos;
        int x = int.Parse(s) - int.Parse(Key.ToString()[keyPos++].ToString());
        BYTES.Add(byte.Parse(x.ToString()));
    }

    byte[] ENDBYTES = new byte[BYTES.Count];
    int counter = 0;
    foreach (byte item in BYTES)
    {
        ENDBYTES[counter++] = item;
    }
    return UTF8Encoding.UTF8.GetString(ENDBYTES); // deciphered data
}