When someone is watching over your shoulder, it’s second nature to cover up your keyboard before typing in a password on your computer, or even unlocking your phone if you still use a pin passcode. But there’s another place where you should be cautious: the front door. Hackers could be recording the sounds that your keys make while unlocking your doors, in a distinctly 21st-century lock-picking attack.
Earlier this year, computer scientists at the National University of Singapore outlined the vulnerability in a paper published in the journal Proceedings of the 21st International Workshop on Mobile Computing Systems and Applications.
he researchers describe a stealth attack, called SpiKey, that involves only the slightest bit of social engineering: simply stand close enough to a person sliding their key into the lock, and use a smartphone to record the metallic clicking sounds as the key turns inside. From there, signal-processing technology (which turns analog signals into digital signals) converts the sounds to match up with the bittings, or deep-cut ridges, in the key. With that information, all a hacker must do is create a 3D-printed model.
Specifically, the research team is interested in pin tumbler locks, which use a series of protruding pins to keep the internal plug from rotating unless a user inserts the correct key. That key will have ridges that, when pushed into the plug, will lift the pins to the correct height to align with the shear line. These are some of the most common locks in use today, and are often found in doors, bicycle locks, and even most vending machines. Unlike digital keys, they are vulnerable to lock-picking operations.
Still, lock-picking has significant limitations, the authors note. “For instance, lock picking requires specific training and practice, and easily raises suspicion because it requires the attacker to insert into the lock a pair of specialized tools which is inevitably noticeable,” they write in the paper. “In addition, lock picking inherently grants a single entry upon successful picking and also leaves traces because the picking scratches the surface of the pins.”
Luckily, the researchers working on SpiKey have gotten ahead of the criminals, figuring out how to use modern technology to outsmart the old lock-picking style. This kind of research is vital because it’s meant to be preventative and get ahead of the bad actors before they discover new modes of intrusion. Other recent examples of this brand of cybersecurity research include spying on conversations with a light bulb, watching the amount of data that a webcam produces to see if anyone is home, and using inaudible waves to trigger Siri.
The hacking technology would go something like this: from a few centimeters away, the person conducting the attack records audio of the victim unlocking their door. For these purposes, a smartphone works just fine, the researchers found, but other microphone equipment could also suffice if it’s strong enough.
With proprietary software, the team removed noise from the audio file and calculated the distance between each ridge in the key, known as the “bitting depth.” The team posted a video online that includes these isolated clicking sounds, alongside a visual depiction of the audio’s frequencies over time, called a spectrogram, to show what the process looks like. So in theory, your new-age burglar better have working knowledge in software.
Through this proof-of-concept work, the researchers were able to simulate a scenario wherein they could reduce the pool of candidate keys from 330,000 options down to just three—pretty good chances if you’re in the business of breaking into homes or storage lockers.