Wednesday, March 23, 2016

Automotive Remote Keyless Entry Security

Recently there has been another round of reports on the apparent insecurity of remote keyless entry devices -- the electronic key fobs that open your car doors with a button press or even hands-free.  In this case it's not a lot to get excited about as I'll explain, but in general this whole area could use significant improvement because there are some serious concerns.  You'd think that in the 20+ years since I was first involved in this area the industry would get this stuff right on a routine basis, but the available data suggests otherwise. The difference now is that attackers are paying attention to these types of systems.

The latest attack involves a man-in-the-middle intercept that relays signals back and forth between the car and an owner's key fob:

Here's why this particular risk might be overblown.  In systems of this type typically the signal sent by the car is an inductively coupled low frequency signal with a range of about a meter.  That's how the car knows you're actually standing by the door and not sipping a latte at a cafe 10 meters away.  So having a single intercept box near the car won't work.  Typically it's going to be hard to transmit an inductively coupled signal from your parking lot to your bedroom with any reasonably portable intercept device (unless car is really really close to your bedroom).  That's most likely why this article says there must be TWO intercept devices: one near the car, and one near the keys.  So I wouldn't worry about someone using this particular attack to break into a car in the middle of the night, because if they can get an intercept box onto your bedroom dresser you have bigger problems.

The more likely attack is someone walking near you in a shopping mall or at an airport who has targeted your specific car.  They can carry an intercept device near your pocket/bag while at the same time putting an intercept device near your car.  No crypto hack required -- it's a classic relay attack.  Sure, it could happen, but a little far fetched for most folks unless you have an exceptionally valuable car.  And really, there are often easier ways to go than this. Attackers might be able to parlay this into a playback attack if the car's crypto is stupid enough -- but at some point they have to get within a meter or so of your physical key to ping it and have a shot at such an attack.

If you have a valuable car and already have your passport and non-contact credit cards in a shielded case, it might be worthwhile putting your keys in a Faraday cage when out of the house (perhaps an Altoids box).  But I'd avoid the freezer at home as both unnecessary and possibly producing condensate inside your device that could ruin it.

The more concerning thing is that devices to break into cars have been around for a while and there is no reason to believe they are based on the attack described in this article.  They could simply be exploiting bad security design, possibly without proximity to the legitimate transmitter.  Example scenarios include badly designed crypto (e.g., Keeloq), badly designed re-synch, or badly designed playback attack protection for RF intercepts when the legitimate user is transmitting on purpose.  Clever variations include blanket jamming and later playback, and jamming one of a pair of messages for later playback. Or broken authentication for OnStar-like remote unlock.  If the system  has too few bits in its code and doesn't use a leaky bucket rate limiting algorithm, you can just use a brute force attack.

Here's a video from which you learn both that the problem seems real in practice and that folks like the media, insurance, police, and investigators could do with a bit more education in this area:

Note that similar or identical technology is used for garage door openers.

On a related note, there is also some concern about the safety of smart keys regarding compliance with the Federal safety standard for rollaway protection and whether a car can keep running when nobody is in the car.  These concerns are related to the differences between electronic keys and physical keys that go into a traditional ignition switch. There have been some lawsuits and discussions about changing the Federal safety regulations:

1 comment:

  1. Greatly admire you posts on embedded software.
    But I see we now do need to worry about the keys on the dresser with the recent "video" showing actual relay attack and car theft from outside a house.


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