Security Engineering, 3rd Edition

CHAPTER 21Network Attack and Defence

Simplicity is the ultimate sophistication.

– LEONARDO DA VINCI

There's no security here – keep moving!

– RICHARD CLAYTON

21.1 Introduction

In this chapter I'm going to try to draw together the network aspects of security in a coherent framework. This is not straightforward as much of network security is practical engineering; a purist from computer science might see the field as one bodge piled on top of another. And network security may not be that important to many developers: if you write apps for Androids and iPhones that talk to services on AWS or Azure, then you can leave much of the worry to Amazon or Microsoft.

But many organisations need to pay attention to network security, and there are some visible strategic trends. For twenty years, it was accepted that firms would have a trusted internal network or intranet, protected from the Internet by firewalls; while taken to extremes by defence and intelligence organisations with classified internal networks, milder versions were seen as best practice by most normal firms. And some industries have no viable alternatives. For example, the protocols used in industrial control systems – DNP3 and Modbus – don't support encryption or authentication, as they evolved in the days of leased lines and private radio links. By the late 1990s, control systems engineers were attaching sensors and actuators to IP networks, as they were cheaper – and then realising that anyone in the world who ...