A security layer for the popular utility Distributed Network Protocol (DNP) is proposed, limiting the effectiveness of cyber attacks on critical infrastructures with essential confidentiality. Ongoing automation of critical infrastructures, including power, gas and water, increases the responsiveness of control operations and the number of utility devices. This ongoing automation, therefore, increases cyber attacker capabilities to disrupt utility operations and, therefore, create serious security challenges. These security challenges result in manufacturer challenges that are not readily met by current commercial security implementations. The security layer presented in this paper meets the security challenges and manufacturer challenges and handles utility characteristics.