Trust, but verify: Why and how to establish trust in embedded devices

Francillon, Aurélien

A lot of research efforts have been put into constructing secure systems. However, experience has shown that, while there are many products which have a good level of security, others are really insecure. Some are security devices: security is at the core of their purpose; while other are not. We nevertheless often rely on the their security in our daily life and their failure can have serious consequences. In this paper, we discuss why we are in this situation and what we can do to improve the situation. In particular, we defend the thesis that more transparency and more openness in embedded systems hardware and software will foster a more secure ecosystem. First, there is an economic problem. Besides being a difficult problem to solve correctly, security is most of the times expensive. Second, trust is something that is not blindly granted but that is
earned by verifying it. Currently, trusted computing mechanisms often rely on unconditional trust on the systems manufacturer. However, users have too few ways to verify that the systems are trustworthy other than blindly trust the manufacturer. We
should design systems here the users, i.e., the devices owners, can decide whom and what to trust. We call this Design For User Trust, where users are in control of the system. Finally, one can only trust a system fully if he can inspect it. Unfortunately, the first security measures that are implemented in embedded systems often prevent such an independent analysis (e.g., deactivation of a debug port, secure boot, encrypted file
system, obfuscation). But such measures are more hiding the problems (making it difficult to discover software vulnerabilities) than solving it. They are often useful in securing a system (slowing down an attacker) but should not jeopardize our ability to analyze them. We call this Design For Security Testing. We conclude that more research is needed to make it easier to build secure systems, in particular, in the areas of concrete architectures for Design For User Trust and Design For Security Testing.

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