Security Engineering, 3rd Edition

CHAPTER 7Distributed Systems

A distributed system is one in which the failure of a computer you didn't even know existed can render your own computer unusable.

– LESLIE LAMPORT [1125]

What's in a name? That which we call a rose by any other name would smell as sweet.

– WILLIAM SHAKESPEARE

7.1 Introduction

We need a lot more than authentication, access control and cryptography to build a robust distributed system of any size. Some things need to happen quickly, or in the right order, and matters that are trivial to deal with for a few machines become a big deal once we have hyperscale data centres with complex arrangements for resilience. Everyone must have noticed that when you update your address book with an online service provider, the update might appear a second later on another device, or perhaps only hours later.

Over the last 50 years, we've learned a lot about issues such as concurrency, failure recovery and naming as we've built things ranging from phone systems and payment networks to the Internet itself. We have solid theory, and a lot of hard-won experience. These issues are central to the design of robust secure systems but are often handled rather badly. I've already described attacks on protocols that arise as concurrency failures. If we replicate data to make a system fault-tolerant, then we may increase the risk of data theft. Finally, naming can be a thorny problem. There are complex interactions of people and objects with accounts, sessions, documents, ...