Leaving Room for the Bad Guys

When designing a crypto protocol, or building a large security architecture, no competent designer ignores considering the bad guy, and anticipating his plans. But often we designers find ourselves striving to build totally secure systems and protocols, in effect writing the bad guys entirely out of the equation. In a large system, when you exclude the bad guys, they soon muscle their way in elsewhere, and maybe in a new and worse way over which you may have much less control. A crypto protocol with no known weaknesses may be a strong tool, but when it does break, it will break in an unpredictable way. This talk explores the hypothesis that it is safer and better for designers to give the bad guys their cut, but to keep it small, and keep in control. It may not just be our systems but also our protocol building blocks that should be designed to make room for the bad guy to take his cut. The talk is illustrated with examples of very successful systems with known weaknesses, drawn primarily from the European EMV payment system, and banking security in general. We also discuss a few too secure systems that end up failing in worse ways as a result.

Authors and Affiliations

1. Cryptomathic Ltd, 329 Cambridge Science Park, Milton Road, Cambridge, CB4 0WG, United Kingdom

   Mike Bond

Editors and Affiliations

1. Software Engineering Institute, Carnegie Mellon University, 4500 Fifth Avenue, 15213, Pittsburgh, PA, USA

   Sven Dietrich

2. CRCS DEAS, Harvard University, Maxwell Dworkin 110, 33 Oxford Street, 02138, Cambridge, MA, USA

   Rachna Dhamija

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