The classic definition of the cornerstones of information security are:

• Confidentiality, meaning that the data that you send or receive can not be read by others.
• Integrity, the data is valid, has not been tampered with and originates from the authenticate source.
• Availability, the data is available when it is needed.

When we apply these criteria to control system environments we see that only one of these elements, availability, is present. Control systems were designed with availability as the overriding criteria to such an extent, because of the nature of the environments in which they existed in the past, they seemingly ignore the other two criteria.

The majority of control systems do a very poor job with data confidentiality and integrity. This is especially true when these criteria are applied to the huge legacy system install base.The devices that communicate on the network lack the computational horse power to ensure confidentiality through encryption, and integrity through strong authentication and hashing.

They (the communication protocols “spoken” by control systems) were never designed to provide security, and in their current state of old serial protocols wrapped in TCP/IP wrappers then sent across the network, they are almost universally in some way exposed to outside environments, be it exposure to the corporate network, a DMZ, or in the worst case directly to the internet.

The main impetus for ignoring security considerations was that the communications were not exposed to the outside in any way.  Besides, “no one but system engineers understand these protocols any way.” The old panacea of security through obscurity.

And so the industry is left with Defense in Depth. An approach by which multiple layers or perimeter defense leave control systems like a good piece of candy, a hard crunchy exterior and a soft chewy center. And at times because of mis-configurations, poor planning and poor execution the hard exterior is even missing.

In many situations the most difficult aspect of Defense in Depth based perimeter security is correctly identifying the perimeter and what assets to actually defend. An asset owner may have good firewall policies for both ingress and egress into the control system environment from “normal”channels, yet have poor if any defense for wireless devices installed at a remote substation, or no authentication required on dial in connections.

As most of these products have roughly a 20 year life cycle perimeter control becomes the only remedy against cyber intrusion. A peroiod exacerbated by the fact that the perimeter is vanishing, as stated by many industry pundits [see here & here].

The majority of legacy systems have weak, if any, authentication, clear text password exchanges, rampant use of default passwords and accounts. They have no integrity controls. Because of the nature of the legacy systems once an attacker has a toe hold into a control system network he already “owns” the network. If the Defense in Depth fails, the control system becomes a playground.

And yet little is being done do remedy these inherit weaknesses in upcoming products. As the preponderance of the industry is based on long entrenched legacy systems, new products have to be backward compatible, which ensures, rather than cures the inherent problems in control system security. Some new products even exasperate the situation by offering a myriad of outward looking TCP/IP services in the PR jargon of user friendliness.

The cost to completely revamping these systems and replacing them with systems where true security is a guiding design principle is incredibly prohibitive. And who should bear these costs? Vendors, the federal government, asset owners and in turn consumers? No one wants to shoulder the costs of revamping the infrastructure.

As the consequences to attacks against these systems are so much greater than your normal “hack” (people can actually die as the result of a control system attack, a consequence more disturbing than having to clean up a credit mess in the case of cyber identity theft), the “risk” of such an attack is also greater. 

Is Defense in Depth then sufficient?  Do multiple layers of perimeter defense cure the inherent weaknesses at the core of control system technology?  They seem at best a buffer against a portion of attackers, and at worst when poorly implemented a mere speed bump, but how long until inherently secure communication protocols become the industry standard?