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After 9/11, the US instituted a policy of opening and searching checked baggage any time something suspicious was found on a scan. Initially, this meant locks were un-ceremoniously cut off large numbers of bags. Then the agency implementing the policy, the Transportation Security Administration (TSA), came up with the idea of licensing a lock design that contained a back door — a special keyhole to which only the TSA would have the master key.

All-in-all, aside from everyone having to buy new, cheesy locks for their luggage, the system has worked okay until now. This month, using a photo mistakenly allowed by the TSA — and published by The Washington Post — a enterprising solid modeler has uploaded a 3D-printable model for a master key. Now anyone with an upmarket 3D printer can make his or her own key. More importantly, the black market will no doubt be flooded with those keys as a result — rendering the several-hundred-million TSA-approved “Travel Sentry” locks not much more useful than cable ties.

If the problem only extended to airplane travel, that would at least limit the scope of the problem. But most travelers keep the TSA-approved locks on their bags during the rest of their trip — in hotels, taxis, or other public places — exposing them to theft throughout.

This is why master keys and back doors are such a bad idea

Some lessons need to be learned over and over. Every time a system is built with a back door or master key, something eventually goes wrong. Perhaps the biggest surprise in this case has been how long it took. The Travel Sentry lock system is not only in use in the US, but in many major airports around the world. For this to be the first time a master key design has leaked seems unlikely, but it is certainly the first time it has been made this public and widely accessible.

The TSA and The Washington Post realized their mistake shortly after the photo went live, but by then it was too late. It had already made its way around the web and into the hands of a 3D modeler in France. He couldn’t test the model files he uploaded to Github, but they were downloaded and used by a Canadian system administrator to print a working TSA master key in PLA plastic, which worked immediately.

TSA-approved locks suck anyway, and what to do about it

The dirty secret of TSA-approved locks is that they’re actually really poor locks to begin with. There are videos all over the Internet showing how you can pick them with everything from a pair of paper clips to a gas cap key. TSA-approved locks are also all tiny and not capable of standing up to much in the way of bolt cutters. In fact, thousands of them are ripped off luggage accidentally by baggage conveyors every year.

So, in high-crime areas, travelers have learned to take additional precautions. The simplest thing to do is tie some type of strap around your bag. At a minimum, that will slow down a potential thief — whether they pick your lock or simply pop the zipper. Even more effective is to wrap your bag in several layers of plastic wrap. Many international airports with theft problems offer this service either for free or for a small fee.

The most extreme solution is to travel with a checked firearm (it can even be a flare gun). That requires you to have your bag inspected by hand, and then locked with a non-TSA lock of your choice. It is a lot more hassle, but until there is a better solution, it is being used by some who have to check very-high-value items.