Passkeys and PRF extension

If you have a use case in mind for the PRF extension, please tell us about it through Feedback Assistant!

These are definitely not theoretical use cases. Allowing client side encryption enables users to retain sovereignty over their data and service providers an ability to store it without a need or desire to view it. Data vaults are one example https://identity.foundation/edv-spec/#encrypted-storage

Companies like Bitwarden are already taking advantage of this mechanism in Chrome https://bitwarden.com/blog/prf-webauthn-and-its-role-in-passkeys . In the realm of non-custodial digital wallets it would be a big UX and security advancement removing any need to access private keys server-side, or for a user to be forced to securely store/remember a key phrase.

We would like to use PRF to protect the user data within our services by using the PRF salt as basis for the HKDF. Given the heavy penalties in case of GDPR breaches, it would really mean a lot for service providers if the user data could be protected completely by the WebAuthn authenticators. However, this would require that all web browsers/platforms support PRF (for "cloud" authenticators, the PRF extension could even be emulated by the "cloud" authenticator provider). For the moment only Google Chrome/Edge desktop versions support PRF (if the native authenticator supports HMAC-SECRET), which from a practical point-of-view renders PRF useless for the moment.

@garrett-davidson This is all but theoretical. Given the GDPR, the industry should really push PRF support like crazy.

Another use case for PRF is protecting identity wallets. PRF can be used to derive encryption keys that encrypt/decrypt identity data stored locally in a browser or remotely on some cloud storage. This currently works in Google Chrome. A demo of such a wallet can be viewed in the video embedded in a recent Yubico blog: "The first working demo of a web based EU digital identity wallet leveraging FIDO open authentication standards"

Voicing my support for this extension as well. It will open up many opportunities to use client side encryption bound to authentication with passkeys.

Hi all,

I just wanted to add onto this thread.

After further discussion with an Apple employee; while they cannot speak to future plans or timelines, the use cases for the Pseudo-random function extension (prf) in WebAuthn L3 are well-understood by their team and have "no philosophical objections to implementing."

Again, this is NOT a confirmation that Apple will indeed implement this extension into their OS', but I figured it is important information for those who have not already received the memo.

@garrett-davidson regarding real life examples - I am developing a SaaS platform for psychotherapist to help them manage their office and clients and as a part of that there is also possibility manage client session notes within the app. As that is highly sensitive data, I am encrypting it on the browser, so that there is never a plaintext version on the server. However, due to the lack of prf extension, I am unable to use passkeys to unlock this data, though I am using them to login to the app. So the UX is not that great - people can log in with passkeys, but when they want to use notes part, they need to enter a separate password, which is used to derive the encryption key.

What is the ETA for this? Certainly enough support and "use cases" shared

For those of you who cannot wait for Apple to catch-up, Bitwarden has prf fully implemented already. It works great.

https://developer.apple.com/documentation/authenticationservices/asauthorizationpublickeycredentialprfassertioninput-swift.struct

iOS 18 has the support for PRF Extension

iOS 18 and later supports PRF passkey extensions, but does macOS support it? When I tested on Sequoia 15.1.1, it appeared not to support PRF.