My mentor, Robert H. Courtney, Jr. was one of the great original thinkers in security. He taught me a number of useful concepts some of which I have codified and call "Courtney's Laws." At key inflection points in information technology I find it useful to take them out and consider the problems of the day in their light. The emergence of what has been called the Internet of Things (IoT) is such an occasion.
Courtney's First Law cautioned us that "Nothing useful can be said about the security of a mechanism except in the context of a specific application and environment." This law can be usefully applied to the difficult, not to say intractable, problem of the Internet of things (IoT). All "things" are not the same and, therefore do not have the same security requirements or solutions.
What Courtney does not address is what we mean by "security." The security that most seem to think about in this context is resistance to interference with the intended function of the "thing" or appliance. The examples de jour include interference with the operation of an automobile or with a medical device. However, a greater risk is the that general purpose computer function in the device will be subverted and used for denial of service attacks or brute force attacks against passwords or cryptographic keys.
Key to Courtney's advice are "application" and "environment." Consider application first. The security we expect varies greatly with the intended use of the appliance. We expect different security properties, features, and functions from a car, a pacemaker, a refrigerator, a CCTV camera, a baby monitor, or a "smart" TV. This is critical. Any attempt to treat all these things the same is doomed to failure. This is reflected in the tens of different safety standards that the Underwriters Laboratories has for electrical appliances. Their list includes categories that had not even been invented when the Laboratories were founded at the turn of the last century.
Similarly our requirements vary with the environment in which the device is to be used. We have different requirements for devices intended to be used in the home, car, airplane, hospital, office, plant, or infrastructure. Projecting the requirements of any one of these on any other can only result in ineffectiveness and unnecessary cost. For example, one does not require the same precision, reliability, or resistance to outside interference in a GPS intended for use in an automobile as for one intended for use in an airliner or a cruise ship. One does not require the same security in a device intended for connection only to private networks as for those intended for direct connection to the public networks.
When I was at IBM, Courtney's First Law became the basis for the security standard for our products. Product managers were told that the security properties, features, and functions of their product should meet the requirements for the intended application and environment. The more things one wanted one's product to be used for and the more, or more hostile, the environments that one wanted it to be used in, the more robust the security had to be. For example, the requirements for a large multi-user system were higher than those for a single user system. The manager could assert any claims or disclaimers that she liked; what she could not do was remain silent. Just requiring the manager to describe these things made a huge difference. This was reinforced by requiring her to address this standard in all product plans, reviews, announcements, and marketing materials. While this standard might not have accomplished magic, it certainly advanced the objective.
Achieving the necessary security for the Internet of things will require a lot of thought, action and, in some cases, invention. Applying Courtney's First Law is a place to start. A way to start might be to expect all vendors to speak to the intended application and environment of his product. For example, is the device intended "only for home use on a home network; not intended for direct connection to the Internet." While the baby monitor or doorbell must be able to access the Internet, attackers on the Internet should not be able access the baby monitor.