A dead man's switch for your computer? • Hacker News Board

Re: A dead man's switch for your computer?

#31

Post by lgeek » Fri, Jan 23, 2015, 7:30 AM UTC

ipsin wrote: post #10

Independent of, and in addition to, other locking schemes, how about an active process that monitors for either high acceleration (the laptop being moved) or noise above a certain threshhold?

I remember writing a script at some point to lock the screensaver in case of high acceleration or if the laptop is tilting by more than a few degrees. The idea was to lock it if was snatched (or just moved around).

However, that would only be effective against a petty thief and not against a forensic team. In that case you'd probable want to additionally flush the filesystems (if you care about data integrity in case of a false positive), overwrite the encryption keys in memory (maybe on disk as well, but then there's no coming back without a backup) and shut down. I wonder if the init scripts prompting for the password, cryptsetup and the LUKS subsystem have been designed to always overwrite copies of the entered password and decrypted keys ASAP.

Re: A dead man's switch for your computer?

#32

Post by lgeek » Fri, Jan 23, 2015, 7:34 AM UTC

taltman1 wrote: post #25

icebraining wrote: post #12

Earlier quoted context omitted.

There's a program for Linux that does the same, but using your phone (or other Bluetooth device) called blueproximity. It had a slight tendency for false positives, though - sometimes it locked the screen even with the device less than a meter away.

I used blueproximity successfully with my Linux laptop. I bought the smallest bluetooth headset I could find ($25), removed all extraneous parts, and carried it on my person (not my bag). It was so small that I didn't notice it. Effectively like two-factor authentication for unlocking my laptop. It's unwise to use your phone for this purpose, because a phone and laptop might both be swiped if you're not holding on to…

I've tried to use blueproximity at some point (mostly for convenience because I sometimes forget to lock my screen), but the range of BT devices is too large for comfort. I could be anywhere in my flat or in the medium-sized open plan office at work and the phone in my pocket would still be in range.

Re: A dead man's switch for your computer?

#33

Post by Alupis » Fri, Jan 23, 2015, 7:43 AM UTC

icebraining wrote: post #12

kator wrote: post #4

I built a program that automatically locks my OSX machine when I get far enough away from it. It uses iBeacon ranging and I have the beacon in my pocket. Debated on sharing with others but I never managed to clean it up enough to be proud of sharing it.

There's a program for Linux that does the same, but using your phone (or other Bluetooth device) called blueproximity. It had a slight tendency for false positives, though - sometimes it locked the screen even with the device less than a meter away.

I had a laptop once that for some reason wouldn't use the battery even on a full charge. So, naturally, as soon as the power cord was pulled out, the laptop crashed.

Would make for a pretty good DMS; being deceiving with a battery attached and the OS reporting a full charge.

I wonder if there's a way to modify the mainboard (knife a lead or something) to be incapable of using the battery while still charging and the OS still being able to get reporting data.

Re: A dead man's switch for your computer?

#34

Post by IkmoIkmo » Fri, Jan 23, 2015, 8:51 AM UTC

fsk wrote: post #19

It's kind of pointless. If the police have already identified you as a target, there are too many other tactics they can use. For example, they could just set up a hidden camera that records you when you are using your PC.

Well for one this is a post in response to the Silk Road arrests in which a DMS would've saved him. Not pointless at all.

Sure over time their methods will evolve but ask Ross if he'd rather have had a DMS or not. It'd be unequivocally yes.

If your point is 'if you're a big enough target, you're pretty much fucked whatever you do given enough time' then yes that's probably true, too.

Re: A dead man's switch for your computer?

#35

Post by bigbugbag » Fri, Jan 23, 2015, 9:04 AM UTC

kator wrote: post #4

I built a program that automatically locks my OSX machine when I get far enough away from it. It uses iBeacon ranging and I have the beacon in my pocket. Debated on sharing with others but I never managed to clean it up enough to be proud of sharing it.

For this to work as a dead man switch, it will have to trigger the lock the instant there's two of that signal. Otherwise one simply has to sniff bluetooth then copy your signal.

Re: A dead man's switch for your computer?

#36

Post by bigbugbag » Fri, Jan 23, 2015, 9:09 AM UTC

thaumaturgy wrote: post #9

What you want is an RFID keyfob/detector. There used to be a writeup on a homebrew version of this at http://hackaday.com/2013/09/07/hidden-rfid-reader-locks-work... -- but the link that article references is rotten now. A sufficiently motivated person should be able to dig up instructions somewhere. A few years ago there were companies that did this for most operating systems, and fairly inexpensively too, but I'm h…

Anything rfid can easily be duplicated.

Re: A dead man's switch for your computer?

#37

Post by bigbugbag » Fri, Jan 23, 2015, 9:10 AM UTC

hayksaakian wrote: post #23

mixologic wrote: post #22

This might work once, for somebody. Then law enforcement would understand what it is for, what it does, and cut the lanyard/string instead of removing the usb stick before apprehending the device.

Which is probably why the author mentioned wearables with Bluetooth. Less conspicuous, and no strings to cut.

and way easier to workaround, nothing to cut simply duplicate the wireless signal.

Re: A dead man's switch for your computer?

#38

Post by pjc50 » Fri, Jan 23, 2015, 9:41 AM UTC

bigbugbag wrote: post #35

kator wrote: post #4

I built a program that automatically locks my OSX machine when I get far enough away from it. It uses iBeacon ranging and I have the beacon in my pocket. Debated on sharing with others but I never managed to clean it up enough to be proud of sharing it.

For this to work as a dead man switch, it will have to trigger the lock the instant there's two of that signal. Otherwise one simply has to sniff bluetooth then copy your signal.

Bluetooth is cloning-resistant if done properly; communications are encrypted and devices authenticated.

Re: A dead man's switch for your computer?

#39

Post by exprL » Fri, Jan 23, 2015, 9:44 AM UTC

bigbugbag wrote: post #37

hayksaakian wrote: post #23

Earlier quoted context omitted.

Which is probably why the author mentioned wearables with Bluetooth. Less conspicuous, and no strings to cut.

and way easier to workaround, nothing to cut simply duplicate the wireless signal.

How would you duplicate a wireless signal that contains an “answer” to a changing challenge (e.g. sign this message with the secret key)?

Re: A dead man's switch for your computer?

#40

Post by avinassh » Fri, Jan 23, 2015, 9:57 AM UTC

I remember reading about that if HDD can be put in a magnetic field, it will be destroyed. If my door/passage can be set to generate magnetic field enough to destroy HDD, then as soon as authorities take out the computer out of your home, the HDD will be destroyed.

But I have no idea how practical is this.