Paper 2024/1503

A Certified-Input Mixnet from Two-Party Mercurial Signatures on Randomizable Ciphertexts

Masayuki Abe, NTT (Japan)
Masaya Nanri, Kyoto University
Miyako Ohkubo, National Institute of Information and Communications Technology
Octavio Perez Kempner, NTT (Japan)
Daniel Slamanig, Universität der Bundeswehr München
Mehdi Tibouchi, NTT (Japan)
Abstract

A certified-input mixnet introduced by Hébant et al. (PKC '20) employs homomorphically signed ciphertexts to reduce the complexity of shuffling arguments. However, the state-of-the-art construction relies on heavy Groth-Sahai proofs for key homormophism, and only achieves honest-user security, limiting broader applicability. This work proposes a novel certified-input mixnet achieving stronger security guarantees, alongside better efficiency. This is achieved by introducing a tailored signature scheme, two-party mercurial signatures on randomizable ciphertexts, that allows users and an authority to jointly sign ciphertexts supporting key, ciphertext, and signature randomization without compromising integrity and privacy. We compare our approach to previous works that employ structured ciphertexts, implement our protocols, and provide performance benchmarks. Our results show that verifying the mixing process for 50,000 ciphertexts takes just 135 seconds on a commodity laptop using ten mixers, underscoring the practicality and efficiency of our approach.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Preprint.
Keywords
MixnetCertified InputsMercurial SignaturesVoting
Contact author(s)
msyk abe @ ntt com
nanri masaya 26n @ st kyoto-u ac jp
m ohkubo @ nict go jp
octavio perezkempner @ ntt com
daniel slamanig @ unibw de
mehdi tibouchi @ ntt com
History
2025-04-30: last of 2 revisions
2024-09-25: received
See all versions
Short URL
https://ia.cr/2024/1503
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2024/1503,
      author = {Masayuki Abe and Masaya Nanri and Miyako Ohkubo and Octavio Perez Kempner and Daniel Slamanig and Mehdi Tibouchi},
      title = {A Certified-Input Mixnet from Two-Party Mercurial Signatures on Randomizable Ciphertexts},
      howpublished = {Cryptology {ePrint} Archive, Paper 2024/1503},
      year = {2024},
      url = {https://eprint.iacr.org/2024/1503}
}
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