Title

Non-Interactive Plaintext (In-)Equality Proofs and Group Signatures with Verifiable Controllable Linkability

Authors

Olivier Blazy (Université de Limoges, XLim, France), David Derler (IAIK, Graz University of Technology), Daniel Slamanig (IAIK, Graz University of Technology), Raphael Spreitzer (IAIK, Graz University of Technology).

Abstract

Group signatures are an important privacy-enhancing tool that allow to anonymously sign messages on behalf of a group. A recent feature for group signatures is controllable linkability, where a dedicated linking authority (LA) can determine whether two given signatures stem from the same signer without being able to identify the signers(s). However, currently the linking authority is fully trusted, which is often not desirable. In this paper, we firstly introduce a generic technique for non-interactive zero-knowledge plaintext equality and inequality proofs. In our setting, the prover is given two ciphertexts and some trapdoor information, but neither has access to the decryption key nor the randomness used to produce the respective ciphertexts. Thus, the prover performs these proofs on unknown plaintexts. Besides a generic technique, we also propose an efficient instantiation that adapts recent results from Blazy et al. (CT-RSA'15), and in particular a combination of Groth-Sahai (GS) proofs (or sigma proofs) and smooth projective hash functions. While this result may be of independent interest, we use it to realize verifiable controllable linkability for group signatures. Here, the LA is required to non-interactively prove whether two signatures link or not (while it is not able to identify the signers). Thereby, we significantly reduce the required trust in the linking authority. Moreover, we extend the dynamic group signature model to cover verifiable controllable linkability.

Venue

Topics in Cryptology - CT-RSA 2016, The Cryptographer's Track at the RSA Conference 2016 (https://jpn.nec.com/rd/event/ct-rsa16.html)

Place and Date

San Francisco, CA, USA, February 29- March 4, 2016.

Publication Reference

Olivier Blazy, David Derler, Daniel Slamanig, and Raphael Spreitzer. "Non-Interactive Proofs for Plaintext (In-)Equality and Group Signatures with Veriable Controllable Linkability". In Topics in Cryptology - CT-RSA 2016, The Cryptographer's Track at the RSA Conference 2016, San Francisco, CA, USA, February 29- March 4, 2016. Proceedings, 2016.

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Bibtex

@inproceedings{bdss16,
Title     = {Non-Interactive Proofs for Plaintext (In-)Equality and Group Signatures with Verifiable Controllable Linkability},
Author    = {Olivier Blazy and David Derler and Daniel Slamanig and Raphael Spreitzer},
Booktitle = {Topics in Cryptology - {CT-RSA} 2016, The Cryptographer's Track at the {RSA} Conference 2016, San Francisco, CA, USA, February 29- March 4, 2016. Proceedings},
year      = {2016},
Publisher = {Springer}
}