Non-repudiation of commitments to a transaction can be good when both parties want to avoid later disputes about the authenticity of these commitments. It requires careful design of the data to be signed, the public key certificates, the policies governing the signature creation and validation processes, and the signature formats to enable validation as long as needed.
Attribute presentation is not designed for this feature. When attribute presentation becomes non-repudiable, it creates legal uncertainty:
1. In court, the verifier may now present the proof of possession as evidence. But this is, at least in the EU, not recognised by default as an e-signature. It is yet unknown if it would be interpreted as such by a court. So the verifier keeps a risk that will be difficult for them to assess.
2. Even if it would be recognised as evidence, the holder may argue that it is a replay of a presentation made in another transaction. Presentation protocols are not designed for timestamp assurance towards third parties, and generally do not include verifiable transaction information.
3. The verifier may protect itself by audit-logging attribute presentation input and output along with publicly verifiable timestamps and verifiable transaction information, and by editing its terms and conditions to claim a priori non-repudiation of any presentation. Typically such a solution would not create the same evidence files at the holder’s side. So the holder would not be able to present as strong evidence in court as the verifier. (This asymmetry aspect needs some more elaboration.)
Non-repudiation is well arranged in EU law for e-signatures. If anyone would want the same for attribute presentation, this should involve changes in law. As far as I can see, non-repudiation is now opportunistically being considered in mDL/EUDI just from an isolated technical perspective.
Another issue with non-repudiation of presentation is that it encourages relying parties to log full transcripts of presentation interactions. It could also encourage supervisory bodies to request such over-complete logging. Instead, relying parties should log the minimum necessary, to avoid developing a honeypot of personal data.
