def __convert_char_hex(message_char):
    """
        Input: message_char - string (one character)

        Output: hex_str - string (hexadecimal value of that character)
    """
    hex_str = hex(message_char)[2:]
    if len(hex_str) % 2 == 1:
        hex_str = '0' + hex_str
    return hex_str
