Biometrics in the age of Pastebin

Let’s go back in time to June, 2012. LinkedIn was compromised and 6.5 million password hashes were released to the internet. Everyone changed their password (right?) and it wasn’t *that* big a deal. Now, let’s jump forward in time, to sometime when biometric authentication becomes more common. In this new era, LinkedIn gets compromised, and 6.5 million hashed fingerprints are released to the internet…so everyone does what? Do users switch the fingers they use for authentication? Biometric authentication is a great idea that, unfortunately, suffers from some serious drawbacks, especially when deployed in the cloud. 

Biometric authentication’s greatest weakness is immutability. Your fingerprints aren’t going to change, and failing some pretty major plastic surgery, your face won’t either. This basically means one big problem: You can’t change a compromised biometric. Do you have any publicly accessible pictures on Facebook? What about videos? Could those be used to hack facial recognition, even with liveness detection? The way your biometric features are set in stone mean there is a much greater responsibility to protect them, and unfortunately you aren’t the only one who bears that responsibility.

Cloud services that leverage biometrics aren’t super common yet, but assuming biometrics catch on, it’s only a matter of time before the marketing types make it happen. How is that data stored? Can you really trust your service provider to take better care of your fingerprint than your password? Millions of passwords get exposed by hacks like the LinkedIn hack every year. Most services require users to register at least two fingerprints to use fingerprint-based auth; that gives users at MAX 10 password resets for an entire lifetime. After that, the data used for authentication starts repeating: which fingers you use for authentication may change, but if an attacker has compromised a fingerprint, they can use that fingerprint to bruteforce any authentication schema that relies on the compromised finger’s data – a kind of known-plaintext attack. That isn’t the only issue with immutability, either. There is a reason best practices recommend using separate passwords for separate services.

If you use biometric authentication for multiple services, the security of your access to those services is linked (just like with a normal password). Basically, you’re trusting every service provider with the password to your other accounts. Maybe that’s okay with you; you’re fine if some social network knows your bank account password. Unfortunately for you, it isn’t that simple. If that social network ever gets compromised, within hours your bank account password will be on Pastebin, and I’ll eat my hat if some enterprising script kiddie doesn’t have a bot testing out username/fingerprint combinations to every bank service they can find. This only gets worse once you run out of fingers to authenticate with. If anyone ever associates all ten fingerprints with your identity, no account you ever create will be safe with biometric authentication again.

Maybe I’m being a little histrionic. That would be totally fair. There are a bunch of practices that could (maybe not totally) mitigate these issues. And, after all, biometrics are supposed to be part of a dual-factor authentication scheme, right? So we’ll at least have a password in addition to our fingerprints. And any serious company who deploys biometric authentication will surely encrypt the data, and keep it somewhere safe, away from the key. Then again, take a look at biometric authentication right now. My coworker Karl wrote a blog about consumer grade fingerprint readers in Lenovo laptops. His conclusion was that the software was pretty lax about storing sensitive data. What happens when practices like that move into realms like banking and health care?

Truth be told, I don’t think this problem is unsolvable. It’s always possible to simply not use biometrics! For anyone who still wants to use biometric authentication, just take this warning and exercise real caution in the storage of your users’ data, and keep in mind that the technology needs some serious refinement before consumer-grade biometric scanners provide any real protection.

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