Hierarchical Deterministic Keys for the EU Digital Identity Wallet

[sander]

An informal working group of specialists from the DC4EU, EWC and Potential consortiums has been collaborating on this document:
Hierarchical Deterministic Keys for the European Digital Identity Wallet (PDF v0.1.0) (Source on GitHub)

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As of today, ARF 1.4 provides no complete and interoperable solution for key management, that can be industrially deployed at scale and used across the whole ecosystem.

HDK is a viable solution to some EU Digital Identity Wallet key management challenges. It enables the management of an unlimited amount of keys using a single secret. It also allows the use of existing secure cryptographic devices with common algorithms.

HDK is applicable to specific credential schemes, including batch-issued one-time-use attestations and BBS#.

After today’s presentation to DG CNECT, we want to continue the dialogue with the European Commission about the proposed solution in this document, and how to include this in the Toolbox. We have included specific feedback on the ARF high-level requirements to make sure that the EU Digital Identity implementation addresses the key management challenges in an interoperable and scalable way. This should provide a solid basis for legislation in the Implementing Acts.

Expert participants from DC4EU:

• John Bradley (Yubico)
• Leif Johansson (Sunet)
• Nikos Voutsinas (GUnet)

Expert participants from Potential:

• Antoine Dumanois (Orange)
• Sander Dijkhuis (Cleverbase)
• Zeff Sherriff (Bundesdruckerei)

[sander]

As discussed today, next to this conversation on HDK specifically, I have opened related issues.

• HDK Feedback: Enable distributed key management #283
• HDK Feedback: Enable asynchronous remote generation of WSCD-bound keys #284
• HDK Feedback: Make trust evidence provision to Attestation Providers optional #285
• HDK Feedback: Encourage cryptographic algorithms that avoid patent risks #286
• HDK Feedback: Make proof of association optional #287

These issues likely require detailed exchanges to better understand the context and each other’s detailed points of view.

[sander]

HDK is now available as an Internet-Draft at CFRG: draft-dijkhuis-cfrg-hdkeys

It is mentioned in at least three ARF discussion topics:

• https://github.com/eu-digital-identity-wallet/eudi-doc-architecture-and-reference-framework/issues/327
• B - Re-issuance and batch issuance of PIDs and Attestations #332
• C - Wallet Unit Attestation (WUA) and key attestation #333

As input for these topics, we have published an analysis comparing HDK with the Proof of Association (PoA) work, outlining common ground and contentious issues: Feedback to resolve HDK and PoA issues in the ARF