Deniability for Signed Credentials: Revisiting the Authenticated Channel vs. Signed Data Debate in the EUDI Wallet

Magdalena Bertram; Anja Lehmann

Paper 2026/1648

Deniability for Signed Credentials: Revisiting the Authenticated Channel vs. Signed Data Debate in the EUDI Wallet

Magdalena Bertram

, Fraunhofer AISEC

Anja Lehmann

, Hasso Plattner Institute

Abstract

The European Digital Identity Wallet (EUDI Wallet) is currently adopting ECDSA-based signed credentials as part of its core architecture, which raised concerns that such designs inherently lack plausible deniability compared to authenticated-channel approaches such as the German electronic identity card. This paper revisits this perceived trade-off and argues that it is not a property of signature schemes themselves, but of the credential presentation protocol. We show that standard cryptographic techniques - specifically lightweight OR-proofs over the native ECDSA verification equation - can be used to transform signed credential presentations into non-transferable, verifier-bound transcripts. Our contribution is not a new cryptographic primitive, but a careful instantiation of well-established techniques within the EUDI context, showing that deniability can be added to signed credentials while preserving their deployment advantages.

Note: This is an extended version of a paper accepted for publication in \emph{Availability, Reliability and Security --- ARES 2026 Workshops}, Lecture Notes in Computer Science, vol.~16900, Springer Nature. This version includes full security proofs as additional material.

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Published elsewhere. Major revision. Availability, Reliability and Security - ARES 2026 Workshops, LNCS vol. 16900, Springer
Contact author(s): magdalena bertram @ aisec fraunhofer de
anja lehmann @ hpi de
History: 2026-08-15: approved; 2026-08-10: received; See all versions
Short URL: https://ia.cr/2026/1648
License: CC BY

BibTeX

@misc{cryptoeprint:2026/1648,
      author = {Magdalena Bertram and Anja Lehmann},
      title = {Deniability for Signed Credentials: Revisiting the Authenticated Channel vs. Signed Data Debate in the {EUDI} Wallet},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/1648},
      year = {2026},
      url = {https://eprint.iacr.org/2026/1648}
}