Paper 2019/081

Practical Group-Signatures with Privacy-Friendly Openings

Stephan Krenn, Kai Samelin, and Christoph Striecks


Group signatures allow creating signatures on behalf of a group, while remaining anonymous. To prevent misuse, there exists a designated entity, named the opener, which can revoke anonymity by generating a proof which links a signature to its creator. Still, many intermediate cases have been discussed in the literature, where not the full power of the opener is required, or the users themselves require the power to claim (or deny) authorship of a signature and (un-)link signatures in a controlled way. However, these concepts were only considered in isolation. We unify these approaches, supporting all these possibilities simultaneously, providing fine-granular openings, even by members. Namely, a member can prove itself whether it has created a given signature (or not), and can create a proof which makes two created signatures linkable (or unlinkable resp.) in a controlled way. Likewise, the opener can show that a signature was not created by a specific member and can prove whether two signatures stem from the same signer (or not) without revealing anything else. Combined, these possibilities can make full openings irrelevant in many use-cases. This has the additional benefit that the requirements on the reachability of the opener are lessened. Moreover, even in the case of an involved opener, our framework is less privacy-invasive, as the opener no longer requires access to the signed message. Our provably secure black-box CCA-anonymous construction with dynamic joins requires only standard building blocks. We prove its practicality by providing a performance evaluation of a concrete instantiation, and show that our non-optimized implementation is competitive compared to other, less feature-rich, notions.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. Minor revision. 14th International Conference on Availability, Reliability and Security (ARES 2019)
Contact author(s)
stephan krenn @ ait ac at
kaispapers @ gmail com
2020-02-26: last of 2 revisions
2019-01-28: received
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Creative Commons Attribution


      author = {Stephan Krenn and Kai Samelin and Christoph Striecks},
      title = {Practical Group-Signatures with Privacy-Friendly Openings},
      howpublished = {Cryptology ePrint Archive, Paper 2019/081},
      year = {2019},
      doi = {10.1145/3339252.3339256},
      note = {\url{}},
      url = {}
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