Security through diversity


Someone asked me the other day whether I thought the United States was vulnerable to a large scale “cyber” attack. While I have no doubt that any particular organization can be compromised, what comforts me at the national level is the sheer diversity of our systems. We have – unintentionally – employed a very effective defensive strategy known as “security through diversity.”

Every organization’s IT system is composed of multiple layers: credential systems, firewalls, intrusion detection systems, tripwires, databases, web servers, OS builds, encryption schemes, network topologies, etc.  Due to a variety of factors — competitive markets for IT products, lack of standards, diversity of IT managers’ preferences — most institutions make independent and varied choices at each layer. This, in turn, means that each insitution requires a customized attack in order to be penetrated. It is therefore virtually impossible for a single software program (virus, worm) to infiltrate a large portion of them.

On the web, a particular form of uniformity that can be dangerous are the centralized login systems like Facebook Connect. But this is preferable to the current dominant “single sign on system”:  most regular people use the same weak password over and over for every site because it’s too hard to remember more than that (let along multiple strong passwords). This means attackers only need to penetrate one weak link (like the recent Rock You breach), and they get passwords that likely work on many other sites (including presumably banking and other “important” sites).  At least with Facebook Connect there is a well funded, technically savvy organization defending its centralized repository of passwords.

I first heard the phrase “security through diversity” from David Ackley who was working on creating operating systems that had randomly mutated instances (similar ideas have since become standard practice, e.g. stack and address space randomization). It struck me as a good idea and one that should be built into systems intentionally. But meanwhile we get many of the benefits unintentionally. The same factors that frustrate you when you try to transfer your medical records between doctors or network the devices in your house are also what help keep us safe.

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