Tag Archives: application security

Security Test-Driven Development – Spreading the STDD-virus

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Agile development with short release cycles have been here for a while now. Most of us want fast feedback loops and many even Continuous Delivery with changes in production software everyday. However, most of us also want secure software and the question is: Can security engineering keep up the pace? A fast feedback that your production website has been hacked is not so nice.

Security is a quality attribute of your software, just like performance. If you don’t want to be surprised by bad performance in production, what do you do? You test and design for it of course and you preferably do so continuously from the start.

In my experience, the same however cannot be said of security. It is very often relegated to a once a year penetration-test activity. Not really an agile way of working is it? Not a secure one either since untested software is released as often as everyday. There must be a better way of working which allows us to both work in an agile way and to verify security on the way.

In the security field people like Gary McGraw have long been advocating ways of “Building Security In”. The Microsoft MVP Troy Hunt also proposes that you should “Hack yourself first”, instead of just waiting for the pentesters. Shouldn’t it be possible to weave these security activities into the process the same way as it is possible with normal testing activities using TDD? Indeed I, as well others believe it is so. Let’s look at how small extensions to an agile process can work in this direction.

Extending Sprint planning to deal with security

To start off you must first know what the requirements are. In a normal agile project this is done by eliciting User Stories from the customer or the Product Owner.

Let’s take an example of an online e-Commerce site. A User Story might be “As a customer I want to be able to add a review of a product so that information about products can be shared between customers”.

This works very well for traditional functional requirements, but for non-functional requirements a little extra thought is needed. In the case of security requirements it is often useful to state a requirement in a scenario that should NOT happen. In our case we shall call these scenarios “Abuser Stories”. These stories are non-technical descriptions of bad things you want to make sure you avoid. An Abuser story for this site might be:

“An attacker uses the Review Product-function to spread malicious Javascript”. Another might be: “An attacker abuses the Review Product-function to gain unlimited access to the database”.
A Product Owner might not be able to come up with these stories himself, but might need the help of a security engineer to help him with finding these threat scenarios.

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