Master Keys

http://www.schneier.com/blog/archives/2012/10/master_keys.html

by mikegerwitz • 14 years ago

173 54 14 years ago

jgrahamc3• 14 years ago

If you follow through to the story that shows a picture of the keys two things are notable: these are pretty easy keys to duplicate (especially given the nice clear photograph of them) and it was the New York Post who both broke the original story and posted a picture of the keys (face palm).

finnw• 14 years ago

I was slightly surprised that they just look like regular keys. I was half expecting them to have special grooves, or protrusions, or magnets or something.

btilly• 14 years ago

Nope. Just a regular key that hits a specific set of pins that are required to be there.

If you think about it, designing a lock that takes 2 completely different types of keys would be very difficult. If you don't fit the grooves that a regular key does, you don't fit. So you have to use the same blank. After that it is just the set of grooves that matters.

jes5199• 14 years ago

Some of those keys look ancient! I don't see how a lock keyed to those could possibly hold up to even an amateur lockpick.

lifeisstillgood• 14 years ago

Ancient is the point - at some point after the twenties, it became less and less cost effective to have someone at the building 24/7 - and the rise of electronic security (alarms basically) provided everyone with a two-factor reassurance that the system was still secure even with distributed master keys.

As long as no-one sold them to the public ...

nnnnni• 14 years ago

Ugh, the NY Post is nothing but a tabloid -- from Fox, no less.

MattRogish• 14 years ago

Master keys are the very definition of "security through obscurity". As Bruce says, this is a very hard problem and one that has been reasonably solved for a long time. However, thinking that sophisticated terrorists or criminals have been unable to exploit this merely because they haven't been to eBay is naïve to the extreme.

nathan_long3• 14 years ago

>> Master keys are the very definition of "security through obscurity".

Not really. A key is like a physical password. Security by obscurity is "I'm betting you don't know what kind of lock/encryption I'm using." Legitimate security is "I won't give you my key/reveal my password."

Just because there's a secret doesn't mean you're Doing it Wrong. "Something you know" is a valid authentication factor.

mikeash5• 14 years ago

Security through obscurity is, ultimately, betting your system on something you can't ever change.

A key that you give out to thousands of people and cannot be changed afterwards ceases to be a key and becomes an intrinsic part of the system.

With a real key, when a leak like this happens, you invalidate the leaked key and issue a new one. In this particular case, they're basically stuck hoping that nobody does anything nefarious with this key.

The mere existence of a physical key does not make it security through obscurity. It's the fact that the same physical key is distributed to thousands of people with no good way to control them all or compensate for a leak that makes it security through obscurity.

Avenger42• 14 years ago

As I see it, though, the issue is that I can walk up to your house, notice that you're using a XYZ-brand lock as I knock on the door, give you a standard door-to-door spiel, you turn me away and you forget about me before you're back on your couch.

Half an hour later I have a master key to your house because I Googled "XYZ master key" and filed the appropriate key blank to match. How do you combat that?

That's the security-by-obscurity argument - once the information on "XYZ master key" is available, your house is compromised and you can't fix it by rekeying, only by replacing all XYZ-brand locks with a different brand.

njharman• 14 years ago

No. Obscurity is not the only or even any of the protection keys master or otherwise provide. Regardless of whether attacker knows of the existence of master key or not. They still need a key.

A master key represent reduction of security (by bypassing depth of security and putting more eggs in one locked basket). Both security trade-offs for convenience.

precisioncoder3• 14 years ago

I feel like if this were to be replaced by a digital solution it would be essential that multiple vendors would be used. There was a big vulnerability that occurred with hotel locks that seems like it would have been mitigated by multiple vendors. http://www.schneier.com/blog/archives/2012/08/hotel_door_loc...

buro92• 14 years ago

Given when such keys need to be used, a digital solution would also need to work in emergencies such as flooding, fire, and partial destruction (door and lock internals fine, outer lock and door severely damaged).

I imagine that it's easier just to stick with the good old master keys.

I've long believed that most locks are not there to stop professionals, they're just there to stop the opportunist.

If you're at peace with this then there's little advantage spending an extremely large amount of money putting in place a sub-standard digital solution.

The existing system is good enough.

bjxrn• 14 years ago

I've heard it before: "Locks are there to keep honest people honest."

The lock on your front door won't stop someone breaking into your house. Or rather: your lock likely isn't the weakest point when it comes to keeping people out.

However, with the master keys it's not just about getting into places where you shouldn't be able to go, it's also about more or less locking a whole place down by disabling elevators. I can imagine you could put something a bit more complex to disable something which already requires electronics to function.

mikeash5• 14 years ago

Do most locks really need to work in emergencies?

My house has no master key, after all. If the fire department needs to get inside, they will break the door down. That is the universal master key for any situation, and my understanding is that fire departments are well equipped for this.

Why not simply not have a master key, with the understanding that the door will be destroyed in the event of an emergency?

jasonkolb• 14 years ago

I assume the lock industry will be added to the list of industries that will lobby like hell against 3D printer technology. I'm putting the over/under on a 3D model of these keys showing up on the Net at about a day.

andr• 14 years ago

Key-making machines are already widespread and much cheaper than 3D printers.

camiller• 14 years ago

equally, a set of metalworking files and key blanks/brass stock are much cheaper than key-making machines.

CaptainZapp• 14 years ago

I was wondering about the same thing regarding those TSA locks.

My fancy new luggage comes with combination locks and in addition with one of those TSA locks.

The thing is, how many different lock combinations are they? (My guess: less then a dozen) How widely must the master keys be distributed? Well, in multiple instance to every airport in the US and then some How long until a bunch of dodgy luggage handlers own a set of those locks?

While the consideration not having to break your luggage is nice the implementation seems not very secure to begin with (yeah: I know: neither are luggage locks, but still)

jgrahamc3• 14 years ago

Details analysis of the TSA locks: http://download.security.org/tsa_luggage_locks_report.pdf

smackfu• 14 years ago

That's depressing.

Especially the part about how you can just bust open the zipper on a locked bag anyways.

nathan_long3• 14 years ago

That's an excellent starting point to explain why we shouldn't accept encryption that has backdoors.

andrewingram• 14 years ago

I basically use luggage padlocks as an over-the-top way of making sure the zipper doesn't come undone accidentally. Of course, I could achieve the same thing with a paperclip.

ezpassmac• 14 years ago

I think that this article represents the need for digital locks. So far, no one has disrupted this space and there is a HUGE market. Think of everyone who lives in an apartment/house in the world. Now take only 1% of 1% of 1% and that's going to be a very large number of people who would signup.

morsch• 14 years ago

There are digital locks, e.g. unlocked using RFID tokens. Carrying around a token is not much more convenient than carrying around a physical key, although it does come with other benefits (e.g. easier revocation). Using something like NFC and unlocking a door using your phone would be nice, but on the other hand I don't want to be locked out just because my phone ran out of power.

Anyway, it's not a trivial modification, ie. just replacing the lock, because the digital lock needs power to process the key and unlock the door. As long as that's necessary, the initial investment and the increased complexity make the benefits moot to me personally. If you have some sort of door knob action maybe you could harness that to generate a small amount of power sufficient to unlock the door?

cerebrum• 14 years ago

What if there is a power outage? You say battery? What if the battery fails? And you would still have the problem of keeping thousands of batteries and electronics running, those fail too. In the end you are adding complexity to the system, so physical locks still have advantages.

xyzzy1233• 14 years ago

I know this is uncharitable, but after reading your post, I immediately envisaged a future where locks are web controlled, and the security of people's front doors relies on a shiny Web 2.0 site not having an XSS or CSRF somewhere. Uh oh.

That said, I would be really interested to see a shot at something new in this area.

Most of the current companies follow the OEM -> reseller model. Their customer is actually building and access maintenance companies, not the end user.

fusiongyro• 14 years ago

I'm not in favor of it, but it's worth noting that the lock on all of our front doors right now is not terribly hard to pick. When the SWAT team wants in, they dispense with the lock altogether by just battering through the door. I suppose if that wasn't fast enough for you, you could blast your way in. The lock-picking technique would not work on correct code--but producing proven correct code is very expensive and unpleasant, so not likely to happen. And you'd still be susceptible to the other two options.

My point is that security is not primarily a technical problem--or at least, there isn't a 100% technical solution, and probably never will be. In practice we benefit a lot from looking innocuous and having neighbors that know us and like us. The main thing keeping people out of your home isn't the lock, it's the inconvenience and unpleasantness of what would most likely happen if they were caught.

jamii• 14 years ago

A lot of houses in South Korea have electronic locks. We got locked out on Christmas eve because the batteries didn't work properly in the cold.

potatolicious2• 14 years ago

> "I think that this article represents the need for digital locks."

I disagree. We are talking about keys to critical infrastructure - fire doors, elevator overrides, utility areas of subway systems.

These are all resources that need to be accessible in a power outage or disaster situation. I do not want our firemen to be locked out of where they need to go because some digital lock lost power.

There is a reason in traditional engineering emergency overrides and shutoffs are mechanically implemented and don't go through a computer.

jl6• 14 years ago

Digital lock with built in dynamo (pull down lever?) to generate the miniscule power required to operate it?

gjm11• 14 years ago

> take only 1% of 1% of 1%

1. Why? I mean, I get that it's a very small fraction, but if you're considering a scenario where you only get a very small fraction of the market, why should that very small fraction be more plausible than, say, 1% of that?

2. OK, so the population of the world is about 7 billion, and 1% of 1% of 1% of that is 7,000. That's not actually so very enormous, especially as you're not going to get a lot of recurring business. (Unless you're envisaging that people pay on a subscription basis for the continued use of the locks on their home, in which case I think 0% of 0% of 0% is a better guess for the likely market penetration.)

jgrahamc3• 14 years ago

Also, if you are interested in actual master keys, Matt Blaze's paper on the subject is a classic: http://www.crypto.com/masterkey.html

"n a recent research paper, we describe weaknesses in most master-keyed lock systems, such as those used by offices, schools, and businesses as well as by some residential facilities (particularly apartment complexes, dormitories, and condominiums). These weaknesses allow anyone with access to the key to a single lock to create easily the "master" key that opens every lock in the entire system. Creating such a key requires little skill, leaves behind no evidence, and does not entail engaging in recognizably suspicious behavior. The only materials required are a metal file and a small number of blank keys, which for many locks are readily available."

rikf• 14 years ago

Like a smart terrorist/activist/pranker couldnt learn how to pick locks.

jdechko• 14 years ago

Michael Brady, commenting on the original article, said it best.

"Master keys are a convenience, not a security measure."

Master Keys

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