Equivocal Broadcast Encryption: Adaptively-Secure Optimal Distributed Broadcast Encryption from Lattices

Rishab Goyal; Saikumar Yadugiri

Paper 2026/792

Equivocal Broadcast Encryption: Adaptively-Secure Optimal Distributed Broadcast Encryption from Lattices

Rishab Goyal, University of Wisconsin-Madison

Saikumar Yadugiri

, University of Wisconsin-Madison

Abstract

We present the first Distributed Broadcast Encryption (DBE) scheme from falsifiable lattice assumptions that achieves adaptive security with optimal parameters (short public/secret keys and ciphertexts). Our construction enjoys transparent setup and offers flexible instantiation: we achieve a succinct CRS in the Random Oracle Model, or a long CRS in the standard model. Previously, no lattice-based DBE simultaneously achieved adaptivity and optimal parameters in either setting. To achieve this, we introduce a new methodology for proving adaptive security: $\textit{Equivocal Encryption Systems}$. This framework operates in two indistinguishable modes: a 'real' mode utilizing standard algorithms, and a 'fake' mode where keys and ciphertexts are jointly sampled with auxiliary trapdoors, enabling the dynamic equivocation of ciphertexts to arbitrary challenge values. While our approach is technically distinct from the celebrated Dual System Encryption (Waters, CRYPTO'09), we believe it could serve as a similarly powerful paradigm for realizing adaptive security across a broad class of lattice-based encryption systems.

Metadata

Available format(s): PDF
Category: Public-key cryptography
Publication info: Preprint.
Keywords: Distributed Broadcast Encryption Broadcast Encryption Lattices
Contact author(s): rishab @ cs wisc edu
saikumar @ cs wisc edu
History: 2026-04-23: approved; 2026-04-22: received; See all versions
Short URL: https://ia.cr/2026/792
License: CC BY

BibTeX

@misc{cryptoeprint:2026/792,
      author = {Rishab Goyal and Saikumar Yadugiri},
      title = {Equivocal Broadcast Encryption: Adaptively-Secure Optimal Distributed Broadcast Encryption from Lattices},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/792},
      year = {2026},
      url = {https://eprint.iacr.org/2026/792}
}