In search of the legal regime for zero-knowledge tests in the construction of the European Digital Identity

Zero-knowledge proof cryptographic protocols allow to prove the existence, possession or knowledge of a data revealing only that the statement made about it is true. This article proposes a research scheme to define the legal value of these protocols for the development of digital identity systems within the European Union. The last amendment to the modification to the eIDAS Regulation, published in February 2023, introduces new legal objects: the European digital identity wallet, the electronic attestation of attributes and the zero-knowledge proofs protocols, these as auxiliary functionality of the two previous objects. The problem is that the proposal does not establish the appropriate legal regime to guarantee the validity of zero-knowledge attestations to the supervisory authorities. In order to address the situation, the article analyses concepts such as blockchain, Self-Sovereign Identity, the eIDAS 2.0 proposal and the union of all these elements in the Hyperledger Indy digital identity commer-cial solution. We conclude that a regulatory framework for zero-knowledge proofs with three pillars - a regulation of computer products, a rule of equivalence between declarations and wallet data with their mathematical transformations and the possibility of imposing acceptance of these tests - can help to open new perspectives in the direction that the European Union's digital identity systems must take and the role that states must assume in balancing public safety, user privacy and market liberalization.