Master lock “picking”

combination lock

Here’s any easy method for backing out the combination of a Master Lock. In a perfect world there would be 64,000 possible lock combinations (403). The construction of the lock prevents this from happening: sloppiness in the dial and the numbers are not mathematically independent. First step is to determine the last number in the sequence. You can then use that number to determine the other possible numbers in the combination. You will end up with about 100 combinations to try, but that’s far better than having to throw the lock out which I’m sure would happen if you had to try 64,000.

UPDATE: x04d sent in a video demo (DivX) (dead link) of how to open a lock in 2 sec. using a padlock shim.

UPDATE: The linked video above has long been dead. Check out our more recent Master lock post for an embedded shimming video

107 thoughts on “Master lock “picking”

  1. this kid i know just finds open locks in in our school and then he takes them home and pops them open with a screwdriver and just watches the internal parts. Easier, and you get free locks.

  2. I hate to say this because I know someone is going to flame me for it and tell me I’m wrong.

    I spent two years of high school trying to open “master locks”. I will guarantee that the pulling up on the locking mechanism (the U shaped thing) will not work on any of the Master Lock padlocks made in the last few years (I’m talking the trademark brand of master lock… not the cheapo ones).

    This trick however will work fine on almost any of the cheapo ones that most people buy.

    Anyway, if you don’t believe me then go try it on a master lock branded padlock.

    1. nickfury is totally wrong. I’ve recently use the hasp tension, number harvesting method to get the third number on two successive new (shim-proof) masterlock combo locks, then use the mod 4 method to reduce the search space, and it worked on both. I’d say that two for two on locks purchased w/in the last week to 6 months proves the methods of masterlock haven’t changed a bit.

  3. As you can see in the video, the master lock that i used is quite new according to the teen colors. I think i’ve bought it last summer in a Wall-Mart. However, I know exactly what you mean: some masterlock seems unhackable using padlock shims and this is because they changed the mecanism a _little bit_. For those models, you just need to put the shims not directly on the retention mecanism because that will block for sure and probably broke the shims if you put to much pressure. You need to put the shim a little away from the middle, lift the shakle a little bit by shaking it up and down, and then move the shim slowly in the middle. It’ll slide itself under the retention mecanism and then you can lift the shackle without problem ^_^

    I’ve passed some time studing locks, it required a lot of pratice ^_^

  4. I learned the combination method posted a year ago and have been successfully opening master locks ever since. It works, I swear. Get so you don’t have to write the possible combinations down, and do it all in your head. Honestly, buy a lock, hide the combination from yourself, and you’ll get a rush when it opens. There are tricks you’ll learn to get faster along the way.

  5. Does the shim thing work for the other kind of Master combination lock as well? The much sturdier looking kind, generally bronze-ish, with four 0-9 dials on the bottom?

  6. There is a method for opening some of those brass combination locks using a thin bit of metal inserted beside the dial. It works by detecting a flat place on the dial shaft.

    I can’t find it right now, but the process (IIRC) was to put this thin shim in one of the end dials, pressing against the shaft, rotate until you find the flat spot, and repeat for each dial.

    That either gave the combination, or a combination that was a fixed offset from the real combination.

  7. dude, what-the-fuck-ever! i am so pissed off!

    i submitted that link as anonymous, and you go and attribute it to some eliot phillips???

    fuck you. this is not the first time this has happened. stop stroking your friends’ cocks, asshole.

  8. There aren’t 40^3 combinations. The markings on the dial are just aesthetic. The locking mechanism only has 10 positions, hence 10^3 combinations.

    As noted earlier, this weakness was corrected in Master Locks several years ago.

  9. I really feel for the blog owners (eliot and vince) who have to put up with all this violence in their comments. I’m glad that the hackers I know in RL have social skills. Just because you’re on the internet doesn’t mean you have to treat everyone like shit.

    Anyway, vince and eliot, keep up the good work, I think they really do appreciate it. I certainly do.

  10. This definitely works, although your fingers will be tired from spinning the dial. I had a Master Lock which I didn’t have the combo too, stuck with it, and got it open this afternoon. It just takes a little bit of patience.

  11. word 17, why pick your way through the front door when you can take a bat to the back window?

    but seriously, lockpicking is cool challenge. Definitely something im in to.

  12. I’m suprised nobody has pointed out how old this is. I read about this on the Internet at least four years ago. It’s probably more like eight years, but I can’t remember.

    Also, it’s not very useful. Going through up to 100 combinations “in the field” is not generally acceptable. And then there’s the fact that combination locks are rarely used for anything other than school and gym lockers. Real lock picking is much more useful.

  13. I dont know if anyone has ever seen this but would it be too hard to hook up a stepper moter to a pic or a basic stamp and have it try all the combonations (using some logical system) really fast? Just an idea.

  14. Do you think any coders out there could make the “masterlock cracker” program into a java app? Just something that could be installed on a cell phone. That way, all you would have to do is figure out the last digit, open the program on your cell, and voila! It would be much more convenient than carrying a laptop around with the prog, or (dare i say) learning all of the math involved!

  15. ive made shims out of hairpins before, not hard to make and last quite a while if you do it correctly. Ive heard of using some metal tape mesure as a shim, sounds good but never gave it a try because hairpins never failed me( except on masterlocks, in which real shims usually will not work)

  16. Orphrey, any idea where to get a shim thin enough to fit in that tiny little space next to the dials on the brass locks?

    Bob, how does one know before blowing a whole bunch of money on boltcutters whether they will be strong enough to cut the lock in question?

  17. josh, I really have no idea. But I was thinking either symbian or java, but more phones can run java apps, so it would seem better suited for that. I have no experience in coding, so I couldn’t help you out there, but as for installing it on your phone, it should be relatively simple.

  18. When I was a teen long, long ago, i figured out a different method to brute force master locks. it was easier then because they didn’t have the “dummy” notches cut in the drive wheel that this guy’s algorithm identifies — just pulling on the shackle while spinning would reveal the last digit.

    The brute-force method is simple: don’t dial the whole digit space every time. first, i only used the numbers 2.5 apart, so I’d start with a first digit of 0, then 2.5, then 5, and so on around the dial until I got to 37.5. (masterlocks are made in great haste at low cost, so getting within a digit or so is usually close enough to open it.)

    The important part i discovered was that by understanding how the “earlier” digit wheels are spun by the later digit wheels, I figured out that i didn’t have to go all the way back and redial all three digits every time. i’d dial the starting digit (usually zero) then go back all the way around a full turn, then stop at the first digit +2.5, and then back to the last digit. Rather than a two-full-spin reset, I simply went forward only to the first digit +5, then back to the last digit. I’d repeat, going back to +7.5, +10, etc., until the second digit was approaching the first at which point I had completely exhausted the first digit. I’d then spin the dial twice for a full reset of the inner dials, and change to the next first digit.

    if i made a mistake, I’d simply spin the dial twice, starting with the same first digit but picking up the second digit where i had left off.

    with not much practice, I was able to spin through two full first digits tests in about a minute, for a max of 20 minutes per lock. my average is probably about 10-15 minutes per lock (there are always a few screwups, and lost counts.)

    Also, with the addition of the dummy detents found in the current crop of masterlocks i found i could no longer spin directly to the last digit. i had to stop at every little indentation in the last wheel and try the shackle at each point. my finger is usually pretty tired after testing all those combos.

    a final note: once the lock is open (or if you simply encounter an open lock as a bonus), peer inside the lock with a flashlight. you can usually see the wheels inside the lock. take the opportunity to manipulate the lock until you’ve lined up all three notches by eyeball. make note of the combination you dialed (say you saw 10-32-24) now, add (or subtract, i can never remember which) about 10 to each number (yielding 20-2-34, note the wrap around the number 0). in any case the real combination will always be some fixed offset from your observed combination.

    have fun!

  19. Please select one of the following as a standard HACKADAY comment:
    1) This is a hack? No way dude, this isn’t a hack at all! You don’t know anything!

    2) This is so old. I knew about this back when I was in diapers.

    3) Sure, but this is the crappy way to do it. I invented a special method of doing it which is far superior. But I’m not giving away my secrets, because then you’d know I’m full of it.

  20. the old master locks can be opened by kicking them, like on school lockers, hold it up so the back is facing you (it will be almost upside down) give it a good kick and it should pop open. it doesnt break the internals either.

  21. I’ve made a couple of padlock shims, i’d shy away from soda cans – you’ll end up with a lot of cut fingers – very painful for your everday hacker to type with those cuts too! haha

    a good metal i’ve found is the metal off of floppy disks (i’ve tested with a few lying around the office and “CH” have worked the best for me) If need be i’ll post a tutorial on making them. Beware that some floppy disks metal is weaker than others, and some is a *smigget* thicked than others. Mess around until you get a good one. Also these shims weaken over time and only work for about 3-5 padlocks… Becareful when using them so you don’t end up breaking it in the lock. This metal is also useful because it’s pre-rounded so you get less cuts :)

    here’s an ascii diagram of what it looks like, first flatten it out…
    _ _ _ _ _ _ _ _ _ _
    | |
    | |
    | |
    | _______ _______ |
    || | | ||
    ||_______| |_______||
    |_ _ _ _ _ _ _ _ _ _|

    Then you cut them up and you can make two… one for larger locks and one for smaller locks…

    _ _ _ _ _ _ _ _ _ _
    | |
    | _ _ |
    | / | | |
    | _ _/ |_| _ _ _|
    _ _ _ _| |_ _ _ _ _
    |_ _ _ _ _ _ _ _ _ _|

    The top one has worked best for me…

  22. I liked the cell phone thing, but i m working on my calculator way.I have the (actually i rent it form school) those TI graphing calculator, it takes many stuffs even mario games , so i m trying to load this programme too.Just started the Scratch programming after understanding the logic of this stuff.I alwyas wanted to do this, after seeing those movies where people open thoses locks (Italian Job)
    Thanks for this post….

  23. 20
    bat to rear window is SO violent! then you still hafta climb or reach thru it. well… ya gotta do what ya gotta do – just check & make sure you werent sent written invitation first: can you see hinge pins? awfully “get smart”, wouldnt you say?

  24. ok…feel free to email me at

    when i was in highschool…. 1985 or so a friend showed me how to read the serial number? on the back of a master lock, and there was this formula you could use…and with a very slight bit of trial/error you could open ANY standard (locker type) combination lock… i could open ANY master lock on any locker in my high school…. did anyone else ever run into this ????? it was amazing…. the TEACHERS would have me open locks of students who forgot their combos….

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.