International Association for Cryptologic Research

International Association
for Cryptologic Research


Scalable Ciphertext Compression Techniques for Post-Quantum KEMs and their Applications

Shuichi Katsumata
Kris Kwiatkowski
Federico Pintore
Thomas Prest
DOI: 10.1007/978-3-030-64837-4_10
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Presentation: Slides
Abstract: A multi-recipient key encapsulation mechanism, or mKEM, provides a scalable solution to securely communicating to a large group, and offers savings in both bandwidth and computational cost compared to the trivial solution of communicating with each member individually. All prior works on mKEM are only limited to classical assumptions and, although some generic constructions are known, they all require specific properties that are not shared by most post-quantum schemes. In this work, we first provide a simple and efficient generic construction of mKEM that can be instantiated from versatile assumptions, including post-quantum ones. We then study these mKEM instantiations at a practical level using 8 post-quantum KEMs (which are lattice and isogeny-based NIST candidates), and CSIDH, and show that compared to the trivial solution, our mKEM offers savings of at least one order of magnitude in the bandwidth, and make encryption time shorter by a factor ranging from 1.92 to 35. Additionally, we show that by combining mKEM with the TreeKEM protocol used by MLS – an IETF draft for secure group messaging – we obtain significant bandwidth savings.
Video from ASIACRYPT 2020
  title={Scalable Ciphertext Compression Techniques for Post-Quantum KEMs and their Applications},
  booktitle={Advances in Cryptology - ASIACRYPT 2020},
  author={Shuichi Katsumata and Kris Kwiatkowski and Federico Pintore and Thomas Prest},