HN's Daeken will expose security flaw in 4m hotel room keycard locks

http://www.forbes.com/sites/andygreenberg/2012/07/23/hacker-will-expose-potential-security-flaw-in-more-than-four-million-hotel-room-keycard-locks/

by ssclafani • 14 years ago

253 138 14 years ago

forbes.com

daeken27• 14 years ago

I'm planning on doing a Reddit AMA for reversing in general -- as well as this work -- in the next hour or two, but if anyone has any questions I'll do my best to answer here. All I ask is no protocol details (paper and full code will be out tomorrow immediately following my talk) and no legal questions. Go wild.

Edit: Since this thread has blown up a bit, we may as well just do it here for real. If you have any reversing questions or background questions or whatnot, feel free.

shimon_e5• 14 years ago

Do you kindly mind only leaking the information on Friday?

Thanks from all us who spend our weekdays living in hotels.

daeken27• 14 years ago

Regardless of which hotel you're in and what locks they use, always use the physical security mechanisms provides, e.g. door chains. Deadbolts are engaged by the lock mechanism and will be retracted by, say, maintenance key cards.

While this definitely opens up new bad things, the message is the same: don't trust the software, trust the physical. Then again, after doing this for a few years, I may be a bit on the paranoid side.

tedunangst• 14 years ago

Do you think all the locks are going to be fixed by Monday?

stfu• 14 years ago

Random question: His former employer [..], sold the intellectual property behind Brocious’s hack to the locksmith training company the Locksmith Institute (LSI) for $20,000 last year.

Are these guys "buying up" security flaws in locks similar to others who sell these kinds of things for software?

daeken27• 14 years ago

Don't know what they're doing, quite honestly. Though I should mention that they didn't buy it from us, they got a non-exclusive license to use the technology. Just wanted to clarify.

Heinleinian• 14 years ago

It's the Locksmith Institute. Locksmiths are who you call to get into a door to something own, but to which you lost the key. So presumably there's situations where a hotel can't get their keys working, and they'd like to have locksmiths in their city who are trained in this. Don't think it's any more complicated than that...

ars• 14 years ago

The article mentions Onity - what about other companies?

daeken27• 14 years ago

Everything I'm releasing is specific to Onity. I can't speak to the security of any of the others, as I haven't looked at them yet, but I'm planning on doing so in the near future. Next up is most likely Ving, though Timelox is a really clever system, so that could be fun.

mpakes2• 14 years ago

Was it necessary to wear a t-shirt that reads "It's fun to use learning for evil!" in the photo shoot for a Forbes spread? This doesn't help the negative perception of the word "hacker". :-/

All due respect to the work you're doing – I'm a former member of the security industry myself (worked on the IPS engine at TippingPoint).

tptacek4• 14 years ago

You don't think this is a little nitpicky? He's at the "Black Hat Briefings".

boredguy8• 14 years ago

Counterpoint: I love that you wore it, I think the content of the article makes it hard to come to a negative conclusion (especially the comments about stopping development), and most anything that supports dieselsweeties.com is a good thing!

sneak3• 14 years ago

Ugh, a dyed-in-the-wool corporate whitehat bitching about a real hacker wearing an ironic black t-shirt while posing for a magazine interview.

It's 2012. Your argument is twenty years late to the discussion. Deal with it.

cchurch• 14 years ago

I didn't even notice the text on the shirt underneath his greasy, unwashed hair.

MartinCron• 14 years ago

It's pretty obviously tongue-in-cheek. He doesn't look at all evil (sorry Daeken, you look kind of... Jolly) and any real evil people don't let Forbes take their picture.

paulgb• 14 years ago

> But on three Onity locks installed on real hotel doors he and I tested at well-known independent and franchise hotels in New York, results were much more mixed

This is a long shot, but I was in a chain hotel in midtown recently and heard someone tampering with the lock, and found the door ajar in the morning. I realize you probably can't name specific hotels, but was one by any chance a chain hotel in midtown around the 11th?

daeken27• 14 years ago

Nope, I was in Europe at the time; we did the photoshoot late last month, though I can't recall when.

michaelbuckbee• 14 years ago

I used to travel fairly extensively for work, on at least 3 separate occasions I had Marriott check me into an already occupied room.

brown9-2• 14 years ago

You don't lock the bolt or the chain mechanism when you stay in a hotel room? Or are you saying they bypassed those also?

nja2• 14 years ago

My university uses Onity locks for universal access with ID cards. This means our campus (and residences) are vulnerable, too, right? Are you aware of many universities that use similar systems?

daeken27• 14 years ago

So, those locks are the CT (commercial, Integra) locks. I strongly suspect that they're vulnerable to roughly the same thing, but I haven't tested them to see for sure. There are two reasons I believe this to be the case: the only difference between the PP20 (portable programmer used in the Onity HT system for hotels) and the CT PP is a swapped out EPROM. Given the similarity of the systems from a high-level perspective and the PP differences, I'd be very surprised if they weren't similarly vulnerable.

At some point I'd love to test the CT side, but 1) the hardware is tough to get hold of, and 2) it's not a very popular system, so it's not that interesting. I think it'd be pretty straightforward, though.

jgrahamc• 14 years ago

It won't be a surprise to learn that these types of locks are vulnerable, but I'll be fascinated to learn the details especially since it sounds like you can get access to an internal bus easily.

The assassination of Mahmoud Al-Mabhouh (http://en.wikipedia.org/wiki/Assassination_of_Mahmoud_al-Mab...) allegedly by Mossad involved attacking an electronic hotel lock to get access to his room:

"A readout of activity that took place on the hotel room's electronic door lock indicated that an attempt was made to reprogram al-Mabhouh’s electronic door lock at this time. The investigators believe that the electronic lock on al-Mabhouh’s door may have been reprogrammed and that the killers gained entry to his room this way. The locks in question, VingCard Locklink brand (Dubai police video, 21:42), can be accessed and reprogrammed directly at the hotel room door."

daeken27• 14 years ago

Yep, bus is clearly accessible on the bottom of the lock.

As for Ving, I think they're going to be next up; spent years honing my skills in reversing this sort of thing, seems like a shame to stop now.

shurane• 14 years ago

How did you hone your skills for years? Have you been working with other lock providers? Or other methods, or just the process of reverse-engineering the software that hardware interacts with?

You are cool, you know that?

screwt• 14 years ago

Could you explain a little more why you didn't go for responsible disclosure to Onity?

In the article you suggest that you don't think they could fix it. Maybe true but shouldn't you (a) give them the oppurtunity to try (just cos you can't spot the fix doesn't mean it's impossible), and (b) give them the chance to say "yep, it's broken - give us 3 months to ship out new locks to all our customers" (yes, highly unlikely I know!).

Given that you sat on this for a year before publishing, there was ample oppurtunity to inform Onity before you publish.

daeken27• 14 years ago

Given the simplicity of the vulnerabilities (as mentioned in the article, you have full and unauthenticated memory access) and the length of time -- over a decade -- that these locks have been on the market, there is absolutely no doubt that they knew about this.

Given that, I felt that they would delay, delay, delay, and delay some more before finally going silent, at which point I would be forced to do this anyway. Simply put, I have zero confidence in their ability to mitigate this properly, and I believe that the only proper course of action is to make this public and let the hotels make themselves secure by whatever means possible.

I know that's a bit of a strange answer, but this is a strange situation; it's taken me a while to figure out the correct course of action, and I feel that this really is the best way for the safety of the public.

Edit: Toned down some of the wording; unnecessary.

akamaka• 14 years ago

That's a completly bogus excuse. The question wasn't why you're releasing it publicly, but why you haven't made any attempt to contact the company beforehand, which you seem to have had a year to do.

Edit: The only reasons I can think of are laziness or just plain not giving a shit about responsible disclosure.

huhtenberg4• 14 years ago

Not cool, dude. Not cool at all. The company might be lazy and ignorant, but it doesn't mean they won't move when faced with a lingering public disclosure. You must give them a chance. What you are planning to do is egoistic, it serves your own interests, and it does that at the expense of people staying in the hotels. How is this even remotely ethical?

wccrawford• 14 years ago

I agree that it's probably futile, but the white-hat thing to do is give them notice. If they say they will not fix it, or ignore you, then you release the info.

If they say they're working on it, you give them a reasonable timeframe for that, and then release it.

That way, you've done everything 'properly', and nobody can say otherwise. With the path you're on, everyone is going to blame you instead of them, even though they're at fault.

Please consider doing this the proper way, even though we both know it's most likely futile.

unimpressive• 14 years ago

Since everyone else replying is telling you what a lazy horrible person you are, I'll go ahead and let you know that I agree. Theres nothing they can really do at this point. And because of that the companies only real option is to just stonewall you for as long as possible.

EDIT: And if it weren't for the long history of large companies suing security researchers for blackmail/etc when they try responsible disclosure I'd have probably sided with everyone above.

st3fan3• 14 years ago

You are acting on assumptions. If you actually talk to them first you will find out what will really happen.

They might actually have a way to deal with this. Maybe the only thing they need is some time.

webjprgm• 14 years ago

Is the obvious fix to make the programming port available only from the inside of the room? That's where the screws for physical bolt locks go.

And you can still have a DC power port on the outside in case of a powered-down door, just no programming access.

Why have they not done it that way???

endianswap• 14 years ago

Probably because if the system glitches out and they can't into the room anymore (even with maintenance keys) then they wouldn't ever be able to fix it?

daeken27• 14 years ago

Well, you can always drill the lock cylinder out, but that's a destructive process. It is possible to do this sort of thing in the right way, they just didn't.

ulope• 14 years ago

Interesting, but it's not as if hotels in general have been high security installations.

Very easy experiment: Just go to the front desk an thell them that you sadly seem to have lost your room card. 90% of the time they will just ask for your room number without requiring any kind of proof that it's actually your room.

otoburb2• 14 years ago

90%?

Anecdotally, I was asked for ID each time my wife or I lost hotel room cards on 4 occasions (3 for me, once for my wife).

I believe they were 2 Courtyard Marriotts, 1 Residence Inn (Marriott), and a Sheraton (don't remember the hotel class).

EDIT: Grammar

petitmiam• 14 years ago

Or there's those hotels where you have to leave the keys at the front desk. Each time you come back you say your room number and they give you the key.

tripzilch6• 14 years ago

Yeah, that was our hostel in NYC. I asked about that, and they kind of looked at me funny, as if I was paranoid or something. If figured the best way would be to semi-jokingly show her my ID regardless and be friendly and chatty in the hopes she'd remember my face with the room number.

In hindsight I might have tried asking for a different room number's key to see if she was paying attention and then quickly correct myself "No, just kidding, my room's 208 not 210. I just wanted to see if you'd give people any room key they ask for". Maybe that would've made them see the issue.

Instead, I took the easy route and made sure to never leave my netbook, passport, tickets, etc in the room (all the rest was replaceable and we were travelling light).

I would have probably done differently if I wasn't in a foreign country on a different continent and still getting used to the cultural uncanny valley of NYC being "almost, but not quite like Europe", so I opted for the safe choice of not being a bother to these obviously hard-working people.

javajosh5• 14 years ago

I was always curious about elock systems, particularly about how they are reprogrammed. Presumably they are reprogrammed by the front desk, centrally, but how does the signal reach the lock? Presumably there must be wires attached (at least for power). So why is there an external port on the lock at all? Also, what is the possibility that a lock exploit could affect the central reprogramming system?

Edit: just read below that these things are battery powered, which raises two questions, first, ok, how are they reprogrammed, and second, how does a hotel not go bankrupt replacing thousands of batteries all the time?

daeken27• 14 years ago

The locks are programmed by the front desk, but then the data is transferred to the Portable Programmer which then is used to update the doors. The doors themselves are not connected to power, but are rather completely battery-driven. The likelihood of anything impacting the front desk equipment is effectively nil.

(Note: This is all specific to Onity locks)

javajosh5• 14 years ago

I'm surprised that's how they are designed. How often do the batteries need replacement? (I realize that this isn't exactly related to your hack, but I'm finding myself fascinated by the economics of maintaining lots of locks. It reminds me of the problem of early computers having to replace vacuum tubes at a certain rate, limiting the size of the machine).

Also, is it the housekeeping staff that reprograms the lock after they clean the room? It seems like it would be very inefficient to send a special person around to reprogram the lock after every check out.

bradfa• 14 years ago

how does a hotel not go bankrupt replacing thousands of batteries all the time?

A microcontroller in sleep state (or similar) draws extremely low power, micro or nano Amps. It only wakes up when it sees data on the card reader, reads the card reader data, and decides if it should open the lock. The motor that unlocks the door only runs for less than a second. Then the whole thing goes back into sleep state.

Hotel doors are only opened 10s of times per day, at most. A pair of couple Amp-hour batteries will last quite a while. Maybe replace them once a year. Tech with an electric screw driver maybe takes 1 minute per door, even a 600 room hotel only costs 2 days of labor once per year (max 1 week, if the tech is slow). That's not that expensive. And the tech's time is 10x the cost of the batteries, coin cells in bulk are dirt cheap.

jcfrei• 14 years ago

let's do this AMA thing right here, because my questions might get lost in the reddit noise. You seem like the prototype hacker to me - what's your personal stack? like OS, text editor, the computer you use daily?

thanks for answering those 3 little questions.

daeken27• 14 years ago

Haha, it seems we already are doing the AMA here.

My stack now is a Lenovo W520 running Ubuntu and KDE, and Sublime Text as my editor. Over the years when I did this, I was running everything from a cheapo, hacked-together box to a 13" Macbook Pro, all running Windows Vista/7.

otoburb2• 14 years ago

Do you use Backtrack at all, or do you simply craft/download/build-from-source your own tools as you need them?

Also, did you switch from Windows to Linux because of the available tools and development environment, or because the Linux desktop had matured enough you could get sh*t done without worrying about driver compatibility issues or other common complaints about Linux [lap|desk]tops?

kristopolous2• 14 years ago

duh? I'm sorry but low security systems like hotel rooms of course have wide vulnerabilities. The front desk will just give out keys based on trust since you don't have to register everyone staying in the room; they don't even have an audit trail if they wanted to use it.

Keyless entry cars are mostly crackable ... garage door systems are trivial, you can bump pin tumbler locks, many home security systems have no backup power. rfid skimmers are cheap and easy-to-use. almost every elock I've seen has the bus readily exposed on the outside (secured by a single screw at best).

There's at most 6 things I can think of that actually do not have trivial security issues.

If I knew I would become famous by informing the press that, for instance, a car model only has a handful of key patterns for millions of cars, I would have done it a long time ago, but I thought such things were just stupefyingly obvious.

twodayslate• 14 years ago

I completely agree with you but I think you should read the following: http://sivers.org/obvious/

lgeek• 14 years ago

> a car model only has a handful of key patterns for millions of cars

This reminds me of growing up in Eastern Europe. Story time: Under the Romanian communist regime, there was only one car factory (Dacia[1]) making cars for personal use. Their main model was essentially the same from the '70s until 2004. For the first 10 years or so after the '89 revolution, Dacia dominated the local car market (because their cars were cheap and really easy to fix).

Now that we have the oh-so-important context, your comment reminded me that when I was a kid, my parents bought a Dacia. What confused me at a time was that random people would periodically ask to borrow the key.

It turns out that for 30-something years, Dacia only used a few models of keys. In fact there were so few that if you locked your keys inside (doors were unlocked by key and they locked automatically) it was feasible to try keys from random cars until one worked.

To be fair, the engine key was different from the door key, and it didn't have this problem. But, getting back to your comment, if you're talking about a recent card model then that's just crazy.

Also, I would have thought that keyless entry systems use correctly implemented public key cryptography. Is that not the case?

[1] http://en.wikipedia.org/wiki/Automobile_Dacia [2]: http://en.wikipedia.org/wiki/Romanian_Revolution_of_1989

kristopolous2• 14 years ago

Many after-market and non-luxury cars can fall victim to a replay attack. More expensive vehicles use something called a rolling code, here's an example chip: http://ww1.microchip.com/downloads/en/devicedoc/21143b.pdf and http://www.atmel.com/Images/doc2600.pdf

Just to be perfectly clear, what you have is a synchronized incrementing number usually using some in-house block-cipher with a 2^16 period. When the car receives a PRN from the RKE, it checks the locality of its current sequence (usually about 2^8) and then if the PRN matches one of them, you are in. So if you have the 2^16 sequence, just skip over every 2^8 and see if it unlocks. That's 2^8 tries; under a second.

If you don't have that, with a few sequences you can deduce the key pretty easily; each PRN is 32 bits; providing you up to 32 bits of information.

Since the payload is an incrementing 16 bit number you have probably 3 bits of entropy on the 32 bits (8 PKE commands between your sniffing). Anyway, assume you have 29 bits from the 32. You also have to toss the 16 bit sequence on the 64 bit source key calculations since it is effectively a salt.

Therefore, you can conservatively get the magic 64-bit key in 6 transmissions assuming there are no sequence collisions of that length. And even if there are, the solution space of the collisions would be quite modest.

Since each transmission has a plaintext serial associated with it (usually a subset of the VIN ... available on the windshield and all), you are not at a loss as to which transmission is which car.

So install your sniffer in an office-building parking structure on Monday, assume codes before 1100 are locks, after 1400 are unlocks, and you are in the car of your choosing by Thursday.

Pretend you don't have this. Pretend you want to do brute force on the 32 bit key-space. There's something called guard time. The idea is that there's a backoff period before another code can be tried. That's usually about a millisecond or two; if at all.

The transmission of the payload is on the order of tens of microseconds.

So generally speaking you can presume that you can do about 1.5m keys an hour.

Now let's say you are a car thief and you go to a lot of new cars ... there's 64 of them (2^6) just to make our lives easy. You have a wonderful consequence of the birthday-problem.

A 2^32 key space with a 2^8 tolerance over 2^6 vehicles ... means (32 - 8 - 6) = 2^18 keys until you should have a match.

Now let's see, you can generate about 2^21 keys per hour ... oopsie daisy. Look what we just did ... Your mean time to unlock one of the cars passes a 50% threshold in all of 4 minutes.

And that's the naive approach, without doing any predictive plaintext attack.

Now let's assume you use both methods together. We aren't talking about much waiting time here.

So I mean yes, the rolling code means you can't just do a replay. Ok, fine ... right ... you have to do a napkin full of math and a little programming. It's not real security.

st3fan3• 14 years ago

I think that making this public is not a very good example of responsible disclosure and I hope there will be a lawsuit before the presentation to prevent the details from being exposed.

I am all about exposing vulnerabilities but I honestly think there needs to be a dialog with the vendor first. Specially for exploits like this where there is a lot at stake.

I find the excuse of 'there is nothing they can do anyway' very poor. I have no doubt that this technique is known to locksmiths and law enforcement and maybe a smaller group of criminals. But making this public and exposing it to the world will allow any criminal with a soldering iron and an Arduino to start exploiting this.

Daeken, you have done an awesome job making this known. Maybe that it enough to get the ball rolling. Or do you just want to do damage for fame and profit?

m0nastic• 14 years ago

This argument has been going around for as long as I can remember, and I think it's incredibly harmful to researchers (whether they be security or other).

Upon discovering the vulnerability, the only real action he could take which would be universally considered unacceptable would be to use that research to go around breaking into hotel rooms (which is illegal).

If he decided to go into business selling devices to bypass hotel room locks, there would also probably be a majority opinion that that isn't really "above-board". Even that isn't necessarily universally agreed on though (as there are a lot of people who argue that providing access to tools isn't criminal)

But he didn't do that either.

He decided that this was a pretty severe vulnerability (made worse by the fact that remediating it isn't trivial), and that he wanted people to know about it.

Hoping that the vendor will sue him to prevent that information from being disseminated is about the worst possible outcome from research of any kind; ignoring the fact that you don't seem to posit any rationale for what exactly they'd be suing about (protected trade secrets? violation of a license agreement?)

The thing about "responsible disclosure" is that it isn't something that exists by fiat. It's an intentional reframing of disclosure policies by vendors to attempt to steer the research community towards doing what's in the vendors best interests.

I understand their desire to reframe that policy, but that doesn't make it "the only ethically responsible way to conduct vulnerability disclosures".

Recently, there's been a lot of news about BMW's being able to be stolen trivially through access to the OBD port on certain models. There's an OSVDB entry for it and everything‡.

That's another example where providing information to the public was considered to be very important (like the issue Cody discovered, it's also not something that can be easily fixed. It's also been ignored by the vendor).

In virtually all other regards, making research public is considered the responsible thing to do.

While I'm not a card-carrying member of the full-disclosure sentiment, I strongly disagree that releasing research publicly is boolean irresponsible.

‡ http://osvdb.org/83707

st3fan3• 14 years ago

I'm not saying he should not publish this at all. I just think it will be more responsible to try to work with the vendor. Right now he has not even made that effort.

wheelerwj2• 14 years ago

so reverse engineering seems cool. What skills do you find most useful/versatile/neat/groovy or otherwise necessary for your reverse engineering projects?

daeken27• 14 years ago

I can't really narrow it down to a single specific skill. When I'm reversing, my steps are generally: figure out how I would design the system, come up with a set of assumptions based on that, check the assumptions as quickly as possible, then refactor your model of the system based on what you find. It's really all about making educated guesses and then checking those; as you gain experience, you start making better guesses.

wheelerwj2• 14 years ago

okay very cool. the scientific method, rinse, repeat. how long have you been reversing?

kylebrown• 14 years ago

What tools do you use for reversing hardware? Did you have to open up the lock and tap into it with something like a logic analyzer? Or was it as simple as creating a DC port adapter so you could read the data from the portable programmer?

daeken27• 14 years ago

So, reversing it was sort of all over the place. I first had to reverse the front desk system and all that; that was primarily done by sitting between the equipment with a serial proxy and working from there. Once I had a good bit of data captured, I'd write software to emulate being one side or the other. Everything is RS232 and RS485, pretty straightforward.

In terms of reversing the actual lock protocol, that was a bit more tricky. First step was tapping the line between the portable programmer and lock with an o-scope (a 70s-era HP scope; only thing I could afford at the time, haha) to figure out the voltage levels involved and the basic properties of the communication. From there, I hit it with the Saleae Logic to see what the communication actually looked like.

From there, I wrote some Python scripts to walk over the data from the logic analyzer and attempt to decode the data. With some tweaking, I managed to finally see some data that I knew, specifically the site code (which I knew from other parts of the system).

After I knew all that, it was a matter of figuring out the actual hardware level. Given that I have effectively no experience with this level of things, this was a lot of asking questions, googling, and experimenting. I knew that it was a one-wire protocol, so by reading up on other one-wire protocols I managed to figure out a lot. Once that was done, everything just fell into place; making the opening device work initially took maybe a day given all the info I had.

stcredzero• 14 years ago

> HN's Daeken will expose

You have my attention...

> security flaw in 4m

sounding really interesting...

> hotel room keycard locks.

Oh. Well, still pretty cool.

EDIT: Actually, this kid of thing needs to get a lot more attention and awareness. I could suggest a certification of some kind, but there's often a reaction against that. But a certification that just indicated:

    - No passwords in plaintext
    - Not vulnerable to replay attacks
    - No "toy" encryption

Would be of great benefit in today's world.

thornofmight• 14 years ago

How did you practice this and discover it? I can't imagine just wondering around hotel rooms playing around with the doors...

daeken27• 14 years ago

I was working on a replacement of the Onity front-desk system at the time, and I suspected it existed for a while. In another comment I detail how I reversed everything, but everything was done on my own hardware, not just random hotels.

mark_g• 14 years ago

The poor hacker's alternative: http://www.youtube.com/watch?v=WAkJRpKeyYg&has_verified=...

rdl• 14 years ago

Any idea what locks Caesars and the Rio use?

tmpaccount2• 14 years ago

I'm not certain, but in the picture from the Forbes article the lock looks exactly like the kind used on many doors in my university - the shape is exactly the same, and ours had the same type of electrical connector in the same place at the bottom of the lock. I remember because I considered attacking this interface before noticing the torx security screw next to the connector; removing this screw allows the panel covering the bottom part of the lock to be removed (the edge of this panel is visible in the Forbes photo), exposing the bolt mechanism of the lock. Turning this mechanism one way opened the lock, turning it the other double-locked it so it couldn't be opened with the proper keycard.

I wonder if any HN readers have access to an Onity lock to check whether this method works on them?

daeken27• 14 years ago

I'm looking at my test lock (which doesn't have panels on it) and it looks to me that there's no way you could access the lock mechanism from the battery panel. With the HT locks I've played with, the locking mechanism sits inside the door, between the lock itself (with the circuit board, card reader, batteries, etc) and the back plate containing the deadbolt and such. Don't think it's vulnerable to what you're describing. However, it should be noted that if it's used in the university, it's almost definitely the Integra/CT line from Onity, which is different.

tmpaccount2• 14 years ago

Ah I see, no doubt a cheaper, lower-security line. Thanks for the info and congratulations on your hack.

HN's Daeken will expose security flaw in 4m hotel room keycard locks

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