The problem(s) with using biometrics

When talking to people about Identity, usually at some point in the conversation, people say "so the future is biometrics?".  And my response is "maybe".....

So here are a few musings on the problems that biometrics face (if you pardon the pun).
  1. Biometrics are to do with authentication of an entity - NOT identity; and the authentication that provides the gateway to whatever identity system you are using. I'm constantly amazed by the amount of security and identity professionals that confuse / mix / interchange these two terms.
  2. Biometrics if stolen cannot be replaced; which is sort of true, but in reality you leave your fingerprints, face and even DNA everywhere. The issue is a replay attack against devices that have your biometric registered, from the "gummy bear" attack against fingerprint sensors, to the dummy head attack against the iPhone 10.
  3. Biometrics cannot be revoked; if you are concerned that someone out there is spoofing your biometric information you cannot toss it away and replace it, as you would a password or a credit card. Yes, there are techniques like salting and one-way encryption that reduce the potential damage. But there will always be a poorly designed system with the potential for a leak of biometric credentials, ruining them for all other systems.
  4. If you rely on a device to validate biometrics then you (as the relying party) must understand the actual model the entity is using to understand;
    • the technology behind the biometric match and what exploits can be used against it
    • the threshold settings on a biometric match within the device / firmware / software
    • the match confidence, or how well the biometric passed validation
  5. As the end user (and the owner of the biometrics) HOW DO I KNOW where my biometrics are stored? When I register my biometrics, I have no actual idea what happens with my biometrics, and have no (easy) way of validating the vendor assurances of "it is secure and well designed".
    I hope that on my fingerprint is stored only on my smartphone, AND in a non-reversible format, AND is not being shipped externally (even on backup).  BUT I HAVE NO IDEA; for all I know my registered fingerprint could be stored and shipped externally as a plain image, and when I authenticate it's being manually verified by a bank of humans in a low wage country.
  6. Biometrics on mobile devices are not the gold standard; many app developers regard the move to biometrics, particularity fingerprint, as far superior to other authentication methods.  Unfortunately the fingerprint API (Android) simply says (binary) "biometric authentication passed"; so on a smartphone where your have enrolled fingerprints from yourself, your partner, best mate etc. then opening the banking app, any of those enrolled fingerprint work; however the bank regards that authentication as the current "gold standard" and applies a higher level of "certainty" that it is the account owner using the smartphone!
So what SHOULD this look like?

For the owner of the biometrics; Provable assurance that my biometrics are secure and exclusively under my control. This means;

  • The only place my biometric should be stored is on a device under my exclusive control
  • That my biometric should not be directly used outside of said device and should only be released as a cryptographic assertion of "sameness"
  • That where a device is only partially under my control (say, a smartphone) then biometrics should only unlock a cached assertion of sameness.

For the receiver of the authentication / identity / attributes (and the entity usually taking the majority of the risk in the transaction), if they are to make a good, risk-based, decision then it is critical that they are able to fully understand how well the entity is connected to the digital infrastructure they are using.

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