Optical gate for mechanical lock

[eric434]

Rig up a dynamo to charge the batteries from the energy needed to open/close the door.

Done right current draw could be absolutely minimal, as well.

[FarmerFreak]

So what you are saying is that you will build your optical-mechanical device, have its power supply concealed inside the container and hope that the user/owner will replace the batteries according to the required interval ?

You do realize that the S&G 2740 has the batteries on the inside and requires someone to change the battery. As a safety protocol if the 2740 runs low on power it (attempt to, time will tell) lock itself in the open position until the batteries are changed.

Rig up a dynamo to charge the batteries from the energy needed to open/close the door.

Done right current draw could be absolutely minimal, as well.

I'm not a big fan of batteries on the inside without an external way to plug in power, even if they can be charged... What we are starting to see with the Kaba Mas model 52 series locks. Is that after 10+ years in use some of the batteries in those locks are refusing to charge enough to open the lock. I'm not sure what percentage of them fail as we've only seen a couple, but it's still enough to be a concern.

[eric343]

Ah, got my old account back.

I like how the 2740 does it, that's a neat idea. Certainly if you don't have to worry about the batteries running flat as long as the lock is in a quiescent state, that's ideal.

Back to security, as I think about the original design some more:
The lock's theoretically perfect aspect only holds until you open it.

When you open a mechanical lock, it does emit some potentially compromising radiation -- sound. And if you have a camera pointed at the safe, you might be able to work out the combination from the movement of the dial, or narrow down the possible combinations a lot by looking at the movements of the person's wrist.

When you dial a combination lock, the lock (due to friction/etc) emits sound while you're turning the dial. The lock also emits sound (a click) when each wheel picks up another one. Those two things might allow an adversary with a sensitive microphone in the same room as the safe to determine the combination, if the lock is opened.

If the adversary has a camera pointed at the safe, looking at the movements of the user's wrist might also give an adversary a rough idea of the combination -- 'he dialed one and a half turns to the left, then half a turn to the right, then three quarters turn to the left.'

Sound we can't realistically eliminate, but we can mask it. One idea would be e.g a bank safe of the type that uses two combination locks: drive the one lock with a motor from inside the safe, determining length and direction of dialing from a random number generator.

(One might switch the motor on and off by having the user extend out what I can only describe as a cylindrical key tray -- the exact word for this I don't remember, but many high security safes have the user drop the (short) key into a sliding metal tray, which then pushes the key into the keyhole deep inside the safe. This device prevents burglars from injecting liquid explosives through a long keyhole.)

Cameras we can at least mostly defend against by screening off the safe, e.g with a double layer of frosted glass illuminated from the inside with a light guide.

[Evan]

When you dial a combination lock, the lock (due to friction/etc) emits sound while you're turning the dial. The lock also emits sound (a click) when each wheel picks up another one. Those two things might allow an adversary with a sensitive microphone in the same room as the safe to determine the combination, if the lock is opened.

If the adversary has a camera pointed at the safe, looking at the movements of the user's wrist might also give an adversary a rough idea of the combination -- 'he dialed one and a half turns to the left, then half a turn to the right, then three quarters turn to the left.'

So your primary concern is designing a safe lock around the "spy vs. spy" scenario where in actuality the foe would drill the safe open and repair it behind themselves rather than try to exactly position a camera to record the combination of the safe in question... A lot less guesswork involved in bringing in a safe expert to open it no matter what...

Your problem would be solved by locating your safe in a room built with poured concrete walls which on the inside the concrete is left exposed on the wall surface and following a set of procedures which require closure of the room door before opening the safe...

(It is very difficult to hide a pin-hole camera somewhere where the pin-hole has to be made through 4 to 6 inches of solid poured in place concrete)

[Evan]

So what you are saying is that you will build your optical-mechanical device, have its power supply concealed inside the container and hope that the user/owner will replace the batteries according to the required interval ?

You do realize that the S&G 2740 has the batteries on the inside and requires someone to change the battery. As a safety protocol if the 2740 runs low on power it (attempt to, time will tell) lock itself in the open position until the batteries are changed.

@FramerFreak:

However the S&G 2740 will not unlock itself to do that, so if the batteries were low but not yet in the danger zone when the container was last closed and secured and then someone who doesn't know any better comes along and plays with the lock trying to open it for a while it is possible that doing that could discharge the batteries to a state where even knowing the combination would not be able to open the container...

It is never a good thing to design an electronic lock which can not have external power supplied to it to deal with battery failures... Even if that external access has to be on the side and protected by a mechanical combination lock and door itself...

~~ Evan

[eric343]

If they have to drill the safe, then good, it's no longer surreptitious entry and the lock has fulfilled its purpose. Then the problem becomes improving the safe, and detecting the drill/repair job.

I would not use bare concrete -- bare concrete has tons of holes which would be perfect for disguising a pinhole! Perhaps some form of degassed/vibrated concrete (to minimize air bubbles and therefore holes) surrounding a frosted-tempered-glass inner room, with an inspection walkway around the outside of the inner room and similar gaps on the top and bottom.

Tempered glass is even more fiendishly difficult to drill through than 6" of concrete: the internal stresses mean the entire pane tends to shatter as soon as you scratch it. (So maybe a safety protective layer of acrylic on both sides of the glass...)

And while we're at it, why not shield the whole place against electromagnetic emissions...

[shadow11612]

So what you are saying is that you will build your optical-mechanical device, have its power supply concealed inside the container and hope that the user/owner will replace the batteries according to the required interval ?~~ Evan

With the internal battery, use the S&G 2740 technique. When the lock's battery is close to dying, it locks open, and cannot be closed until the battery is changed.

[shadow11612]

Ahh never mind, did not see the 2nd page of posts with the same comment on the S&G 2740. Need more coffee.

[shadow11612]

However the S&G 2740 will not unlock itself to do that, so if the batteries were low but not yet in the danger zone when the container was last closed and secured and then someone who doesn't know any better comes along and plays with the lock trying to open it for a while it is possible that doing that could discharge the batteries to a state where even knowing the combination would not be able to open the container...~~ Evan

With the S&G 2740, the "danger zone" lasts for 100 openings. When the battery is drained this point it will start beeping when opened, and give you approximately 100 chances to change the battery. Then it will use a second battery whose sole purpose in life is to give the operator that one last opening and lock the lock open.

Granted if you have ignored 90 or so of the warning beeps, and then someone plays with the lock long enough to kill the main battery and the secondary battery, then you kind of deserve to pay me to drill the safe open.

[eric343]

And while we're at it, why not shield the whole place against electromagnetic emissions...

Now that I think about it... if you want any kind of security these days you're already trying to eliminate electromagnetic emissions. So instead of messing about with poured concrete, spend ~5000 on a shipping container. Thick steel walls are pretty hard to make pinholes in. All you need to do is seal the door gap with copper mesh (easy) or build a proper e/m shielded interior door. Maybe give the inside a coat of conductive paint and connect the whole thing to a grounding stake and your E/M problems are gone. Now add in the aforementioned tempered glass inner room and you're good. Though, since a heavy safe isn't the thing to put on glass, maybe steel plate underfoot.

For extra security, put the container up on posts or blocks in a larger room, and keep the outside under constant video surveillance. Sorbothane isolators or similar between the container and the posts ought to keep any compromising vibrations from the safe lock traveling into the outer room floor (since an adversary could embed a seismic mic in the floor). Though, you'd have to run tests with an audio signal generator + transducer attached to the safe and a microphone outside the container in order to be sure. (Bonus points if you can set things up to make a Bode plot of the whole safe-to-outside-room series of mechanical interfaces!)

[eric343]

Wow, guess I overestimated -- a used 20' shipping container goes for closer to $3000 (CAN):
http://www.bigsteelbox.com/locations/br ... nd-storage

Not sure $2000 would cover all the copper mesh/copper paint/tempered glass/steel/structural elements needed to outfit it, but it would be amusingly paranoid to try.

If anyone tries this, don't forget the self destruct button.*

* http://www.imdb.com/title/tt0120660/

[Lock Jock]

I'm late to the party, but...

Since it's going to be battery-powered to begin with, it could be made impervious to manipulation, microphone spying and radiation attacks (picking attacks, not necessarily destructive attacks) by using a digital, incremental, rotary encoder.

A piezo linear actuator could be used for the bolt or a handle engagement pin.
If the walls are thick steel and not conducive to external magnetic attack, a less costly, normal magnetic motor or solenoid could be used.

These encoders are cheap and are used extensively in stereos for volume control. Most optical encoders of this type are silent (no detents) and, obviously, are not subject to magnetic manipulation or probing.

A simple PIC-micro could be programmed to interpret a change in rotational directions as the trigger to set the current number (just prior to change) in the combination.

Any emissions from the controller board or encoder sending unit could be easily shielded. If desired, the controller board could be mounted remotely from the sender, both sharing the power supply (or two different supplies) and the encoder would send IR pulses to the controller board instead of being hardwired to it -- assuming the safe door is reasonably airtight, no detectable IR would leak out.

An alternative to a prefab electronic encoder could be a coding mirror attached to the sending unit's spindle.
A laser on the controller board would bounce off the mirror back to the controller board -- the controller location could be infinitely variable (may require additional mirrors mounted in various locations) and chosen by the owner so as to make drilling, et al, more dubious. The disc mirror would be painted black (or otherwise opaqued) for a "0" and no paint (shiny mirror) for a "1".

Obvious issues with the latter:
1. Precise alignment of the beam would no doubt prove too difficult for the average user to bother attempting to achieve. Thus, most users would likely mount the controller board in a direct path to the mirror and negate the benefit of target location uncertainty.
2. The controller micro cannot know when to start accepting the code unless the laser is powered continuously to monitor for knob movement, thereby reducing battery life. A solution to this could be an LED and a momentary switch on/in the spindle/knob assembly -- user pushes in knob, LED hits sensor on controller board, board wakes up & fires laser at mirror. Unfortunately, this requires a power source for the sender itself.

In any case, a normal-looking knob could be used on the outside to maintain the facade.

[Lock Jock]

^^
Also, since the lock is electronic, the complexity/length of the combination is limited only by the willingness or ability of the user, and the user can configure this him/herself at will.

[zeepia]

@ Evan: You could disguise the external power terminal so it wouldn´t be so obvious there is something else than an ordinary mechanical lock.

For example there is a line of 20 screws but only numbers 4 and 17 are connected to power wires inside and putting a battery between them will give power to read the lock. Or two holes, diameter 2mm. Put your wires inside to get electricity. Works well when manifacturing a wooden box with a solenoid inside to open the box. No visible lock whatsoever and you can open it with battery and some wires. How about a writing desk with a hidden compartment.

[GWiens2001]

Nice idea, Zeepia. May have to play around with that idea myself. Perhaps a pattern or picture made of blind holes drilled in the lid, with specific holes used to apply an external power supply. Easily do-able.