Cryptographic Challenges In Smart Grid System Security
- Written by Yongge Wang
In this article, challenges are discussed for secure smart energy grid and automation systems from cryptographic technique viewpoints.
The smart grid is a secure and intelligent energy distribution system that delivers energy from suppliers to consumers based on two-way demand and response digital communication technologies to control appliances at consumers’ homes to save energy and increase reliability. The smart grid improves existing energy distribution systems with digital information management and advanced metering systems. Increased interconnectivity and automation over the grid systems presents new challenges for deployment and management.
During February 2011, more than 9,200 electric generating plants produced 312,334,000 megawatt-hours of electricity in the United States. Transmission lines distributed electricity to consumers in a 300,000 mile area. This power infrastructure was designed for performance and the integrated communications protocols were designed for bandwidth efficiency, and cyber security was a low priority. Transitioning from the current energy distribution infrastructure towards a smart grid, we have to overcome the challenges of integrating network-based security solutions with automation systems. Overcoming such challenges requires a combination of new and legacy components that may not have sufficient resources reserved to perform security functionalities. These challenges from the control system and user aspects are discussed below.
According to the American Gas Association Report “Cryptographic protection of SCADA communications”, there are numerous challenges in integrating security solutions into legacy control systems. For example, an integrated solution must consider the following constraints:
- Encryption of repetitive messages.
- Minimizing delays due to cryptographic operations.
- Assuring integrity with minimal latency.
- Intra-message integrity: if cryptographic modules buffer the message until the message authenticator is verified, it introduces message delays that are not acceptable in most cases.
- Accommodating various SCADA poll-response and retry strategies: delays introduced by cryptographic modules may interfere with the SCADA system’s error-handling mechanisms (e.g., time-out errors).
Due to these constraints, classical private key and public key cryptographic solutions are not applicable and could not be integrated into existing control systems.
We have recently designed efficient cryptographic mechanisms to address these challenges and to build cryptographic modules for smart-grid control systems. These mechanisms can be used to build plug-in devices that can be inserted into smart grid networks so all communication links are authenticated and encrypted. In particular, authenticated broadcast protocols are designed so they can be cheaply included into these devices. More details can be found in the paper “Smart Grid, Automation, and SCADA Systems Security,” which will be included in the book “Security and Privacy in Smart Grids” published by CRC Press (2013), and the paper “Securing SCADA Infrastructure Communications” in Int. J. Communication Networks and Distributed Systems (2011).
Another challenge for securing smart grid systems is countering attacks on advanced meter infrastructures. In order for smart grid systems to securely manage remotely- located smart meters, each meter must contain some identifying credentials. A straightforward suggestion could be to use a key management infrastructure such as PKI (public-key infrastructure), which has been successful in e-commerce systems. However, a careful analysis shows it to be infeasible in many scenarios. For instance, smart meters could be mounted either inside or outside a consumer’s home. The energy providers may not want smart meters located within the home because consumers would have access to the authentication key used within. At the same time, if a smart meter were mounted outside the house, an intruder could hack into it, which neither the consumer nor the energy provider wants. In order to address these challenges, smart meters must be equipped with tamper- resistant components such as smart cards.
Smart card-based authentication techniques have been a successful solution for addressing key management challenges in existing cryptographic authentication systems. However, the current smart card protocols may not be applicable to smart meter authentication solutions. For example, in order to authenticate a smart meter with built-in tamper-resistant components that hold the authentication keys, one may need to input a PIN number to unlock the tamper-resistant components. Offline dictionary attacks are a major challenge regardless of whether the smart card is built into the smart meter or is in the physical possession of the service provider’s agents. For example, the attacker could mount an offline dictionary attack against the smart meter (if the smart card is built into the smart meter) or mount the offline dictionary attack against a stolen smart card from a service provider’s agent. As demonstrated in a recent paper “Password Protected Smart Card and Memory Stick Authentication Against Off-line Dictionary Attacks” that appeared in SEC 2012, IFIP AICT 376, existing smart card authentication protocols are all vulnerable to off-line dictionary attacks. Thus they could not be used in smart meter authentication systems. In the same paper, Dr. Yongge Wang has proposed several authentication protocols that could be used in tamper-resistant smart card design and in smart grid authentication systems. These protocols are secure against the offline dictionary attacks discussed above. Similar non-smart card-based remote-authentication protocols that protect against offline dictionary attacks can be found in the paper “Security Analysis of a Password-Based Authentication Protocol Proposed to IEEE 1363,” which appeared in Theoretical Computer Science, 352(1-3):280--287, 2006.