Security Engineering: A Guide to Building Dependable Distributed Systems, Second Edition

Chapter 17. Emission Security

The hum of either army stilly sounds, That the fixed sentinels almost receive The secret whispers of each others' watch; Fire answers fire, and through their paly flames Each battle sees the other's umbred face.

—— William Shakespeare, King Henry V, Act IV

Introduction

Emission security, or Emsec, is about preventing attacks using compromising emanations, namely conducted or radiated electromagnetic signals. It has many aspects. Military organizations are greatly concerned with Tempest defenses, which prevent the stray RF emitted by computers and other electronic equipment from being picked up by an opponent and used to reconstruct the data being processed. Tempest has recently become an issue for electronic voting too, after a Dutch group found they could tell at a distance which party a voter had selected on a voting machine. The smartcard industry has been greatly exercised by power analysis, in which a computation being performed by a smartcard — such as a digital signature — is observed by measuring the current drawn by the CPU and the measurements used to reconstruct the key. These threats are closely related, and have a number of common countermeasures. Researchers have also discovered attacks that exploit stray optical, thermal and acoustic emanations from various kinds of equipment. Such techniques are also referred to as side channel attacks as the information is leaking through a channel other than those deliberately engineered for communication. ...