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Please explain in detail how a digital combination lock works from input to output? Answered

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seandogue

7 years ago

You input the digital code. If it matches the code required, the lock unlocks, if not it doesn't.

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seandogueverence

Answer 7 years ago

Well, yeah...I hadn't considered the query was for someone trying to hack their way into someone's system...but regarding lockout...exactly. Permanent fail after N attempts.

However, if this is a password for a web site (for instance) you may need to go one step further and locally black-list an IP after NxM attempts, where M is the number of re-tries following failure (ie,visitor simply closes browser, deletes history and cookies, waits for system timeout, etc.)

There is also the use of a tunneling pair, in which the password is based on a generated sequence from a piece of hardware that is possessed by a qualified user, but that's really beyond the scope of this conv.

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orksecurityseandogue

Answer 7 years ago

FWIW, permanent fail usually isn't needed. Simply introducing a delay after a few wrong attempts (and, in some, sounding an alarm) is generally enough to ensure that anyone who continues trying will become obvious and be caught.

(Basic principle of practical security systems: You don't usually need perfect security. In most cases, all you really need is security good enough that the idiot will go bother someone else. This is engineering, not science or math; good enough is good enough.)

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orksecurityseandogue

Answer 7 years ago

I had considered that, which is part of why I was trying to push for a more specific statement of what was wanted -- if it was "how do I defeat one", the answer is "if you have to ask, you won't, and depending on what lock it is even an expert may give up on the lock and look for another solution."

And, yes, challenge-and-response systems exist. The best take ideas from some of IBM's early cryptosystems -- not only do they require a cryptographic response from a random challenge, but the algorithm incorporates the date and time, or a "one-time pad" mechanism, so that even if the same challenge comes up again the correct answer will be different every time.

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seandogueorksecurity

Answer 7 years ago

heh...if that had been the question, I'm sure you know what *my answer would have been...I was somewhat obtuse in my answer just in case that was what was being asked, but it wasn't clear enough for my stock answer to the people who gave a bad name to the once honorable title of "hacker".

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orksecurity

7 years ago

What are you actually trying to find out?

Keyboard. Computer and program, typically a microcontroller but the lock may be communicating with a remote computer instead or as well. Solenoid which interacts with the latch or strike in some way to release the door only when appropriate.

Typically, the programming includes a lockout mechanism which will disable the lock if it thinks it's being tampered with.

More detail depends on exactly which lock you're looking at.

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orksecuritysteveastrouk

Answer 7 years ago

Quite possibly. If so, I think he can find more detail with a few simple websearches, including right here on I'bles.

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icengorksecurity

Answer 7 years ago

A 54 year old should Know these things>

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orksecurityiceng

Answer 7 years ago

There are still novices on the web.

If that's what's going on here, I suppose I should repost a pointer to the "how to ask good questions" essay. It's blunt to the point of being slightly rude, but it's excellent advice in how to ask a question in such a way that strangers might be interested in making the effort to provide a good answer:

http://www.catb.org/~esr/faqs/smart-questions.html

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orksecurityorksecurity

Answer 7 years ago

Actually, a homebrew lock *could* be built around a simple hardwired state machine -- but commercial ones aren't.

That's all assuming you mean electronic. If you mean one of the mechanical varieties... that's even more complicated to explain; mechanical state machines get tricky.

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rickharris

7 years ago

Select first number

compare to stored first number if same goto select second number else goto select first number.

Repeat the above for the required numbers in the combination.

For last number successful compare will activate the open lock signal.

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verencerickharris

Answer 7 years ago

Nice! A mechanical dialer can break your lock in almost no-time. (By just trying all possible combination)

Th trick is to have a lock-out period of N ms (milliseconds) after a wrong try _and_ to increase N linearly (Nnew=Nold+x) or geometrically (Nnew=Nold * x with x>1). So a dialer that just test any possible combination has to get it on the very first tries or will have to wait (almost) forever.

The lock might even block completely after x bad tries (depending on where it is used).

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kelseymh

7 years ago

Why not explain it yourself, after doing some research?