Security Engineering, 3rd Edition

CHAPTER 20Advanced Cryptographic Engineering

Give me a rock on which to stand, and I will move the world.

– ARCHIMEDES

Whoever thinks his problem can be solved using cryptography, doesn't understand his problem and doesn't understand cryptography.

– Attributed by Roger Needham and Butler Lampson to each other

20.1 Introduction

Cryptography is often used to build a trustworthy component on which more complex designs can rely. Such designs come from three rather different backgrounds. The first is the government systems world we described in Chapter 9, where the philosophy is to minimise the trusted computing base using mechanisms like data diodes and multilevel secure encryption devices. The second is the world of banking described in Chapter 12 where smartcards are used as authentication tokens while HSMs are used to protect PINs and keys. The third is the world of cryptography research in the 1980s and 1990s where people dreamed of solving social problems using mathematics: of creating anonymous communications so that oppressed groups could evade state surveillance, leading to censorship-resistant publishing, untraceable digital cash and electronic elections that would be impossible to rig. In all these cases, real life turned out to be somewhat messier than we anticipated.

There are even more complex cryptographic components that we use as platforms. But the engineering isn't just about reducing the attack surface, or simplifying our fault tree analysis. In most cases ...