Cracking A Combo Lock In Under 30 Seconds

Forget the combination to your combo lock? Well if you’ve got a 3D printer, an Arduino, a servo and a stepper motor handy — you can build your own Combo Breaker pretty easily. It’s capable of solving any Master combination lock in 8 tries or less.

The creator [Samy Kamkar] is a privacy and security researcher, who absolutely loves finding holes in security. We actually just heard from him at our very own Hack a Day Prize: Los Angeles event, where he talked about his wireless keyboard sniffer he built into a cellphone charger.

He’s previously shown us how to crack a combo lock in 8 tries or less using an online calculator he made. This project is just an extension of that to automate the whole process.

As always he gives an extremely thorough explanation of the project in his build log video — including designing the 3D printed parts! If you wanna build your own it’ll cost just under $100 and you can grab all the necessary info and source files from his GitHub.

[Thanks for the tip Justin!]

21 thoughts on “Cracking A Combo Lock In Under 30 Seconds

    1. I remember a while back, a hack where you could slide a thin piece of metal down the shank and pop the lock similar to using a credit card to jimmy open a door. This is far more elegant and clever. Awesome build!

      1. Doesn’t work with many more modern locks, instead of using a little spring pin they use much more secure ball bearings to lock it. Of note, however, is more often than not those are key locks, not combo.

  1. I figured out at school how to undo a combination bike lock. It was quite easy just pull hard on the lock and turn the wheels, you could feel the movement when the right number was selected. I have to confess to removing the locks from bikes and swapping them round so that people thought they were going mad forgetting their number. Probably locks have got better now but I still wouldn’t trust a combination lock.

    1. The problem isn’t combination locks, its cheap combination locks (especially those from companies like Master Lock who are building to a price rather than building for security).
      A GOOD combination lock from a manufacturer like Sergent & Greenleaf will be much more resistant to opening via these sorts of methods.

        1. The basic design is the same as any other rotary dial combination lock. The cost savings comes in from increased manufacturing tolerances, and reduced varieties of parts to manufacture. If you only have 8 possible combinations, and just offset how the knob is attached, you can save a ton. More possible actual combinations means more variety of parts to make, thus higher manufacturing cost. These locks are more about keeping honest people honest, than actively keeping those out that shouldn’t be getting in.

          1. I’d say that as much as keeping honest people honest they’re for adding time it takes to steal. Every second spend futzing with the lock on something you don’t own is another second for a cop to drive by, or someone who knows the bike’s owner to notice you, or any number of other silly ways to get caught. Yeah it’s not a huge change in risk; it’s about not being the easiest target available.

  2. I had to actually look up what he meant by “an analog feedback servo”. Apparently it is just a regular analog RC servo with the potentiometer line brought outside on another wire.

  3. There are half a dozen projects like this (except for the 3D printing) that have been “featured” here before. What good is the “tagging” if you don’t use it?
    But it is a nice excercise project. I used cardboard for the mechanics, a unipolar stepper motor and a solenoid + micro-switch, driven by Launchpad MSP430 with ULN2003. There is python code for the combination breaking available on the net that I adapted.
    However, the shim method worked much faster to open the lock and retreive the lost combination..

  4. Title should read “Cracking a MASTER Combo Lock In Under 30 Seconds” as it won’t work for any other make. But still thumbs up for the build and implementation.

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