Preface

Summary

It is possible to build a cabin with no foundations, but not a lasting building.

Eng. Isidor Goldreich (1906–1995)

Cryptography is concerned with the construction of schemes that should be able to withstand any abuse. Such schemes are constructed so as to maintain a desired functionality, even under malicious attempts aimed at making them deviate from their prescribed functionality.

The design of cryptographic schemes is a very difficult task. One cannot rely on intuitions regarding the typical state of the environment in which a system will operate. For sure, an adversary attacking the system will try to manipulate the environment into untypical states. Nor can one be content with countermeasures designed to withstand specific attacks, because the adversary (who will act after the design of the system has been completed) will try to attack the schemes in ways that typically will be different from the ones the designer envisioned. Although the validity of the foregoing assertions seems self-evident, still some people hope that, in practice, ignoring these tautologies will not result in actual damage. Experience shows that such hopes are rarely met; cryptographic schemes based on make-believe are broken, typically sooner rather than later.

In view of the foregoing, we believe that it makes little sense to make assumptions regarding the specific strategy that an adversary may use. The only assumptions that can be justified refer to the computational abilities of the adversary.