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Is privacy a security feature?

I’ve spoken a lot about privacy recently: mainly because it’s an important problem. Important enough to hit the headlines; important enough for trade associations and independent developers alike to make a priority. Whether it’s talks at conferences, or guiding people on designing or implementing their apps, there’s been a lot of privacy involved. But is it really on-topic for a security boffin?

The “yes” camp: Microsoft

In Michael Howard and David LeBlanc’s book, “Writing Secure Code, Second Edition”, there’s a whole chapter on privacy:

Most privacy threats are information disclosure threats. When performing threat analysis, you should look at all such threats as potential privacy violations.

In this view, a privacy problem is a consequence of a failure of confidentiality being disrupted. You model your application, taking into account what data it protects, what value the customers put on that data, and how important it is to protect the confidentiality. Personally-identifying information is modelled in exactly this way.

Privacy automatically falls out of this modelling technique: if people can get access to confidential data, then you have a privacy violation (that also looks like a security vulnerability because it appears in your threat model).

The “no” camp: Oh, it’s Microsoft again

A different viewpoint is expressed in another book by Michael Howard (with Steve Lipner this time): “The Security Development Lifecycle”.

Many people see privacy and security as different views of the same issue. However, privacy can be seen as a way of complying with policy and security as a way of enforcing policy. […] Privacy’s focus is compliance with regulatory requirements[…], corporate policy, and customer expectations.

So in this model, privacy is a statement of intent, and security is a tool to ensure your software follows through on your intent. It’s the difference between design and implementation: privacy is about ensuring you build the right thing, and security helps you build the thing right. The two have nothing to say about each other, except that if you didn’t get the security right you can’t make any claim about whether the policy expressed in the privacy requirements will successfully be met in deployment.

The “who cares?” camp: me

The argument above seems to be a question of semantics, and trying to apportion responsibility for different aspects of development to different roles. In fact, everyone involved in making a product has the same goal – to make a great product – and such niggling is distracting from that goal.

Most of my professional work fits into one of a few categories:

  • Learning stuff
  • Making stuff
  • Helping other people make better stuff
  • Making other people better at making stuff than I am

So if, in the process of helping someone with their security, I should be able to help with their app’s privacy too, should I really keep quiet until we’ve solved some quibbling point of semantics?