Paper 2023/137

PAPR: Publicly Auditable Privacy Revocation for Anonymous Credentials

Joakim Brorsson, Lund University
Bernardo David, IT University of Copenhagen
Lorenzo Gentile, IT University of Copenhagen
Elena Pagnin, Chalmers University of Technology
Paul Stankovski Wagner, Lund University

We study the notion of anonymous credentials with Publicly Auditable Privacy Revocation (PAPR). PAPR credentials simultaneously provide conditional user privacy and auditable privacy revocation. The first property implies that users keep their identity private when authenticating unless and until an appointed authority requests to revoke this privacy, retroactively. The second property enforces that auditors can verify whether or not this authority has revoked privacy from an issued credential (i.e. learned the identity of the user who owns that credential), holding the authority accountable. In other words, the second property enriches conditionally anonymous credential systems with transparency by design, effectively discouraging such systems from being used for mass surveillance. In this work, we introduce the notion of a PAPR anonymous credential scheme, formalize it as an ideal functionality, and present constructions that are provably secure under standard assumptions in the Universal Composability framework. The core tool in our PAPR construction is a mechanism for randomly selecting an anonymous committee which users secret share their identity information towards, while hiding the identities of the committee members from the authority. As a consequence, in order to initiate the revocation process for a given credential, the authority is forced to post a request on a public bulletin board used as a broadcast channel to contact the anonymous committee that holds the keys needed to decrypt the identity connected to the credential. This mechanism makes the user de-anonymization publicly auditable.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. CT-RSA
PrivacyAccountabilityAuditabilityTransparencyAnonymous Credentials
Contact author(s)
joakim brorsson @ eit lth se
bernardo @ bmdavid com
lorg @ itu dk
elenap @ chalmers se
paul stankovski_wagner @ eit lth se
2023-02-15: revised
2023-02-06: received
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Creative Commons Attribution


      author = {Joakim Brorsson and Bernardo David and Lorenzo Gentile and Elena Pagnin and Paul Stankovski Wagner},
      title = {PAPR: Publicly Auditable Privacy Revocation for Anonymous Credentials},
      howpublished = {Cryptology ePrint Archive, Paper 2023/137},
      year = {2023},
      note = {\url{}},
      url = {}
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