The Shape of Code

Electronic Evidence and Electronic Signatures by Stephen Mason and Daniel Seng is not the sort of book that I would normally glance at twice (based on its title). However, at this start of the year I had an interesting email conversation with the first author, a commentator who worked for the defence team on the Horizon IT project case, and he emailed with the news that the fifth edition was now available (there’s a free pdf version, so why not have a look; sorry Stephen).

Regular readers of this blog will be interested in chapter 4 (“Software code as the witness”) and chapter 5 (“The presumption that computers are ‘reliable'”).

Legal arguments are based on precedent, i.e., decisions made by judges in earlier cases. The one thing that stands from these two chapters is how few cases have involved source code and/or reliability, and how simplistic the software issues have been (compared to issues that could have been involved). Perhaps the cases involving complicated software issues get simplified by the lawyers, or they look like they will be so difficult/expensive to litigate that the case don’t make it to court.

Chapter 4 provided various definitions of source code, all based around the concept of imperative programming, i.e., the code tells the computer what to do. No mention of declarative programming, where the code specifies the information required and the computer has to figure out how to obtain it (SQL being a widely used language based on this approach). The current Wikipedia article on source code is based on imperative programming, but the programming language article is not so narrowly focused (thanks to some work by several editors many years ago 😉

There is an interesting discussion around the idea of source code as hearsay, with a discussion of cases (see 4.34) where the person who wrote the code had to give evidence so that the program output could be admitted as evidence. I don’t know how often the person who wrote the code has to give evidence, but these days code often has multiple authors, and their identity is not always known (e.g., author details have been lost, or the submission effectively came via an anonymous email).

Chapter 5 considers the common law presumption in the law of England and Wales that ‘In the absence of evidence to the contrary, the courts will presume that mechanical instruments were in order. Yikes! The fact that this is presumption is nonsense, at least for computers, was discussed in an earlier post.

There is plenty of case law discussion around the accuracy of devices used to breath-test motorists for their alcohol level, and defendants being refused access to the devices and associated software. Now, I’m sure that the software contained in these devices contains coding mistakes, but was a particular positive the result of a coding mistake? Without replicating the exact conditions occurring during the original test, it could be very difficult to say. The prosecution and Judges make the common mistake of assuming that because the science behind the test had been validated, the device must produce correct results; ignoring the fact that the implementation of the science in software may contain implementation mistakes. I have lost count of the number of times that scientist/programmers have told me that because the science behind their code is correct, the program output must be correct. My retort that there are typos in the scientific papers they write, therefore there may be typos in their code, usually fails to change their mind; they are so fixated on the correctness of the science that possible mistakes elsewhere are brushed aside.

The naivety of some judges is astonishing. In one case (see 5.44) a professor who was an expert in mathematics, physics and computers, who had read the user manual for an application, but had not seen its source code, was considered qualified to give evidence about the operation of the software!

Much of chapter 5 is essentially an overview of software reliability, written by a barrister for legal professionals, i.e., it is not always a discussion of case law. A barristers’ explanation of how software works can be entertainingly inaccurate, but the material here is correct in a broad brush sense (and I did not spot any entertainingly inaccuracies).

Other than breath-testing, the defence asking for source code is rather like a dog chasing a car. The software for breath-testing devices is likely to be small enough that one person might do a decent job of figuring out how it works; many software systems are not only much, much larger, but are dependent on an ecosystem of hardware/software to run. Figuring out how they work will take multiple (expensive expert) people a lot of time.

Legal precedents are set when both sides spend the money needed to see a court case through to the end. It’s understandable why the case law discussed in this book is so sparse and deals with relatively simple software issues. The costs of fighting a case involving the complexity of modern software is going to be astronomical.