Monday, November 30, 2015

Where is the physical trust boundary?

There's a story of a toothbrush security advisory making the rounds.

This advisory is pretty funny but it matters. The actual issue with the toothbrush isn't a huge deal, an attacker isn't going to do anything exciting with the problems. The interesting issue here is we're at the start of many problems like this we're going to see.

Today some engineers built a clever toothbrush. Tomorrow they're going to build new things, different things. Security will matter for some of them. It won't matter for most of them.

Boundaries of trust

Today when we try to decide if something is a security issue we like to ask the question "Does this cross a trust boundary?" If it does, it's probably a security issue. If no trust boundary is crossed, it's probably not an issue. There are of course lots of corner cases and nuance, but we can generally apply the rule.

Think of it this way. If a user can delete their own files, that's not crossing a trust boundary, that's just doing something silly. If a user can delete someone else's files, that's not good.

This starts to get weird when we think about real things though.

Boundaries of physical trust?

What happens in the physical world? What counts as a trust boundary? In the toothbrush example above an attacker could gain knowledge of how someone is using a toothbrush. That's technically a trust boundary (an attacker can gain data they're not supposed to have), but let's face it, it's not a big deal. If your credit card number was also included in the data, sure no question there.

But as such, we're talking about data that isn't exciting. You can make the argument about tracking data from a user over the course of time and across devices, let's not go there right now. Let's just keep the thinking small and contained.

Where do we draw the line?

If we think about physical devices, what are our lines? A concept of just a trust boundary doesn't really work here. I can think of three lines, all of which are important, but not equally important.
  1. Safety
  2. Harm
  3. Annoyance


When I say safety I'm thinking about a device that could literally kill a person. This could be something like disabling the brakes on a car. Making a toaster start a fire. Catastrophic events. I don't think anyone would ever claim this class of issues isn't a problem. They are serious, I would expect any vendor to take these very seriously.


Harm would be where someone or something can be hurt. Nothing catastrophic. Think maybe a small burn, or a scrape. Perhaps making someone fall down when using a scooter, or burn themselves with a device. We could argue this category for a while. Things will get fuzzy between if the problem is catastrophic. Some vendors will be less willing to deal with these but I bet most get fixed quickly.


Annoyance is where things are going to get out of hand. This is where the toothbrush advisory lives. In the case of a toothbrush it's not going to be a huge deal. Should the vendor fix it? Probably. Should you get a new toothbrush over it? Probably not.

The nuance will be which annoying problems deserve fixes and which ones don't? Some of these problems could cost you money. What if an attacker can turn up your thermostat so your furnace runs constantly? Now we have an issue that can cost real money. What if we have a problem where your 3D printer ruins a spool of filament? What if the oven burns the Christmas goose?

Where is our trust boundary in the world of annoying problems? You can't just draw the line at money and goods. What happens if you can ring a person's door bell and they have to keep getting up to check the door? Things start to get really weird.

Do you think a consumer will be willing to spend an extra $10 for "better security"? I doubt it. In the event a device will harm or kill a person there are government agencies to step in and stop such products. There are no agencies for leaking data and even if there were they would have limited resources. Compare "annoyance security" to all the products sold today that don't actually work, who is policing those?

As of right now our future is going to be one where everything is connected to the Internet, none of it is secure, and nobody cares.

Join the conversation, hit me up on twitter, I'm @joshbressers