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Ring Signatures for Deniable AKEM: Gandalf's Fellowship
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| Conference: | CRYPTO 2024 |
| Abstract: | Ring signatures, a cryptographic primitive introduced by Rivest, Shamir and Tauman (ASIACRYPT 2001), offer signer anonymity within dynamically formed user groups. Recent advancements have focused on lattice-based constructions to improve efficiency, particularly for large signing rings. However, current state-of-the-art solutions suffer from significant overhead, especially for smaller rings. In this work, we present two novel NTRU-based ring signature constructions tailored towards small rings. Concretely, our schemes offer up to 50% reduction in signature size for ring of size smaller than 18 compared to the state of the art ring signature scheme Raptor (ACNS 2019) and the sublinear ring signature scheme Smile (CRYPTO 2021). In particular, for rings of size two, our ring signatures are only 1244 bytes. Additionally, we explore the application of ring signatures in achieving deniability in authenticated key exchange mechanisms (AKEMs), the primitive behind the recent HPKE standard used in MLS and TLS. We take a fine-grained approach at formalising sender deniability within AKEM and seek to define the strongest possible notions. Our contributions extend to a black-box construction of a deniable AKEM from a KEM and a ring signature scheme for rings of size two. Our approach attains the highest level of confidentiality and authenticity, while simultaneously preserving the strongest forms of deniability in two orthogonal settings. Finally, we present parameter sets for our schemes, and show that our deniable AKEM yields ciphertexts of 2 KB when combined with our new ring signature scheme. |
BibTeX
@inproceedings{crypto-2024-34207,
title={Ring Signatures for Deniable AKEM: Gandalf's Fellowship},
publisher={Springer-Verlag},
author={Phillip Gajland and Jonas Janneck and Eike Kiltz},
year=2024
}