Robot Opens Master Combination Locks In Less Than A Minute

A machine that holds a combination padlock and turns its dial, with two padlocks next to it

A common trope in bank heist B-movies is someone effortlessly bypassing a safe’s combination lock. Typically, the hero or villain will turn the dial while listening to the internal machinery, then deduce the combination based on sounds made by the lock. In real life, high-quality combination locks are not vulnerable to such simple attacks, but cheap ones can often be bypassed with a minimum of effort. Some are so simple that this process can even be automated, as [Mew463] has shown by building a machine that can open a Master combination lock in less than a minute.

A machine that holds a combination padlock and turns its dialThe operating principle is based on research by Samy Kamkar from a couple of years ago. For certain types of Master locks, the combination can be found by applying a small amount of pressure on the shackle and searching for locations on the dial where its movement becomes heavier. A simple algorithm can then be used to completely determine the first and third numbers, and find a list of just eight candidates for the second number.

[Mew463]’s machine automates this process by turning the dial with a stepper motor and pulling on the shackle using a servo and a rack-and-pinion system. A magnetic encoder is mounted on the stepper motor to determine when the motor stalls, while the servo has its internal position encoder brought out as a means of detecting how far the shackle has moved. All of this is controlled by an Arduino Nano mounted on a custom PCB together with a TMC2208 stepper driver.

The machine does its job smoothly and quickly, as you can see in the (silent) video embedded below. All design files are available on the project’s GitHub page, so if you’ve got a drawer full of these locks without combinations, here’s your chance to make them sort-of-useful again. After all, these locks’ vulnerabilities have a long history, and we’ve even seen automated crackers before.

28 thoughts on “Robot Opens Master Combination Locks In Less Than A Minute

  1. The most secure part of a genuine Master Lock is its poor quality. Even if you know the combination, and ‘enter’ it perfectly, it may take a dozen attempts. After a month, you need bolt cutters.

    1. i have been locking my bike with the strap from my helmet for 8 years and only had it stolen once. the most secure part of a genuine master lock is that all it’s doing is keeping bored neighbors’ kids out of your toolshed. :) never underestimate the value of not being targetted

  2. do not underestimate human senses and capabilitys
    average sensitivity to feeling a scratch in plate glass
    is @.0001”
    other senses are in line with this,vision,hearing
    smell of some substances is in parts per billion
    if combo locks were secure they would still be used
    now they are for show or cheap covenience

  3. This is the same algorithm used on school lockers when you forgot the combination from 1960 on. They must have been Master locks that were built in. Or at least until they were removed from all the schools (so no one could hide guns and bombs and drugs and all kids had to carry backpacks to class).

    1. I don’t know the actual percentage but I do know that many of the built in locks in school lockers were in fact Master Locks. Also the padlocks that they would issue you for your gym locker. Well, when I was in school on the 70s and 80s, anyway. Those locks were also ridiculously easy to “crack”.

      1. LPL has repeatedly shown how easy it is to open any Master lock, and the combo locks are some of the worst with multiple avenues of failure including a rubber mallet of I remember correctly. Opening them with machine learning might be more useful on another brand.

    1. LPL has shown you bypass them with a shim to deprss the locking shackle. DeviantOllam has shown that there is a public PDF of manuf codes of Master combo locks with their corresponding combination. Why try to solve the combo when you can just look it up? However, not all combos are available.

  4. cool… but the word robot is a bit is leading.

    A few hours ago I warmed my meal in the heating robot.
    Now I’m washing the dirty dishes in the dish washing robot.
    And as I’m typing this my clothes are being dried by the clothes dryer robot, which was a required action since my dirty clothes were cleaned by the washing robot, but that darn thing leaves everything wet.
    In a few minutes I’m going to watch a movie on the put-a-movie-onto-a-thin-piece-of-glass-robot.
    Then when it’s time to go to bed, I need to adjust the wake-me-up-robot to 07:00 and set the alrm notification to the correct radio station, or should I use the beep-beep-beep (which is mostly too loud).
    And because it will be still a bit dark then, I need to switch on the make-a-light robot.
    I make my breakfast and lunch (manually), put it in a box, to take to work, to which I drive using the move-me-around robot.
    At work I watch the assembly robots (at the robot factory) doing their job why I press a button twice an hour (3 times on a busy day), it’s a hell of a job, I know, can’t they make a robot for that?

    Why is everything that we used to call “a machine”, suddenly a robot these days? Why, because it it being controlled by an arduino? I suspect ignorance or clickbait, I’m not sure yet, I guess I use the question answering robot named goo…

    1. It’s going to be ok.

      robot, any automatically operated machine that replaces human effort, though it may not resemble human beings in appearance or perform functions in a humanlike manner.

    2. For some reason a lot of younger people seem to think that the only thing that qualifies as a “robot” is C3PO, or one of Boston Dynamics’ creations. Not true.

      If a machine does something for you on the basis of pre-established instructions–all the more so if it has some decision-making capability–then it’s a robot.

      One of your sarcastic remarks, in particular, made me laugh. A college professor I read about, teaching a robotics course, would start each term asking his students to sketch a rough design for a “dishwashing robot.” After discussing some of the submitted proposals… all of which invariably included android-like machinery, (or at the very least complicated arrangements of mechanical arms,) the prof would make his point by presenting the class a brochure from Whirlpool.

      Yes, your dishwasher is a robot, and yes, so is a programmable automated lock-picker.

      1. +1
        i always have to tell people that VCRs and DVD-players are both robots,
        they just need to be hacked to add-in the siri or cortana lol

        and yes i know most VCRs dont have enough resources to “add siri”…

        but that does not mean its not a robot according to the dictionary.
        ya know, that book with real life verified facts that so many uneducated andor ignorant people like to treat as propaganda.

        1. err i should say all DVD-players and *_most_* VCRs.

          most VCRs contain motors controlled by microcontrollers, often with status LEDs to show us whats being commanded of the motors…

          but some of the first VCRs actually worked much like a mechanically actuated cassette players, the status LEDs were controlled by the mechanics, which is the opposite of a modern one. the big fat chip was merely used as an alarm-clock for the one-shot timer-recording (has to be setup <24h before desired recording.

        2. I have a vague memory of them actually advertising the electrically driven top load mechanisms as “robotized” back in the 80s. Then as those morphed into ubiquitous front load auto loaders the term faded out, it was just a VCR again.

      2. I think full consideration should be given to Karel Čapek’s original invention of the word robot, meaning artificial person. Most people do not think of every complicated machine as being a “robot”, and such misuse only causes confusion.

        If a dictionary definition implies that a dishwasher is a robot, the dictionary is wrong. Dictionaries are not infallible.

      3. Not sure I agree with all of the mocking tones in this thread. However, to be a robot, a dishwasher does just about qualify, as does this robot, as they interact intelligently with an outside thing.
        A music box isn’t a robot, but an automata that plays a piano is. The grey area is the self-playing piano. There, it likely depends on the mechanism – a mechanical playing system that runs off a punch card to move things would just about be a robot, but a digital keyboard playing a tune wouldn’t be.

    3. When I worked with tape and optical media changers, we referred to the changer mechanism as the robot. Their design varied greatly. Most were grippers that moved either along a single axis or on two axis (plane). But some were wild. One model had the single sided drive move up and down and the shelves were in a drum so that the platter/media could be flipped.

      When starting my first job with the media changers, I was warned never to assume that the robot won’t move and to only enter their space (arms, hands, head) when power was confirmed to be disconnected. I never worked with the really large mainframe type models.

      1. We lost an engineer who stuck his head into a piece of equipment to watch it. The head could pull 2 G accelerating and his head was between where the laser was and where it was going.

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