Re: [w3ctag/design-reviews] BBS Cryptosuite v2023 Securing Verifiable Credentials with Selective Disclosure using BBS Signatures (Issue #922)

It has been brought to my attention that the proposal makes claims about unlinkability that are not backed with independent analysis.

The process for constructing and validating a BBS-backed credential involves multiple transformations.  A JSON-LD data model is [canonicalized](https://github.com/w3c/rdf-canon), then this specification defines some HMAC-based transforms for identifiers, which is ultimately passed to BBS in order to produce a proof.

So, while BBS can in theory provide the desired privacy properties and the specification does address the potential for leakage, I was not able to find any formal analysis that supports the claims that are made.  Where I spent a lot of time in the IETF, we are increasingly asking for security and privacy claims like these to be backed by stronger arguments, either through proofs of security or the use of formal/symbolic analysis software packages.

The claims that most interest me are those that relate to [linkability](https://www.w3.org/TR/vc-di-bbs/#selective-disclosure-and-data-leakage).  The document appears to use a novel method of protecting privacy, based on the use of a PRF.  A more thorough analysis of that process would help.

-- 
Reply to this email directly or view it on GitHub:
https://github.com/w3ctag/design-reviews/issues/922#issuecomment-2019124783
You are receiving this because you are subscribed to this thread.

Message ID: <w3ctag/design-reviews/issues/922/2019124783@github.com>