Paper 2026/799

EQuADiSE: Efficient Quantum-safe Adaptive Distributed Symmetric-key Encryption

Sikhar Patranabis, IBM Research India

Debdeep Mukhopadhyay, Indian Institute of Technology Kharagpur

Abstract

Distributed symmetric-key encryption (DiSE), introduced in CCS' 18 enables threshold versions of traditional (symmetric-key) authenticated encryption. In DiSE, the long-term master secret key is secret-shared among multiple parties following a threshold access structure, and both encryption and decryption are performed in a distributed manner. An adaptively secure DiSE, introduced in INDOCRYPT' 20 tolerates adaptive corruptions of the key-holding parties for arbitrary thresholds, while simultaneously retaining efficient encryption and decryption. Unfortunately, all existing instances of adaptively secure DiSE are either quantum-broken (due to their inherent-reliance on discrete log-hard groups), or incur exponential (in the number of parties) online overheads for encryption/decryption. In this paper, we present EQuADiSE -- the first practically efficient, adaptively secure, and plausibly post-quantum construction of DiSE based on the Module Learning with Rounding (MLWR) assumption in the Quantum Random Oracle model (QROM). EQuADiSE is the first adaptively secure quantum-safe instance of DiSE that incurs linear (in the number of parties) encryption/decryption overheads. As a core technical tool of independent interest, we introduce an MLWR-based distributed pseudorandom function (DPRF) that enjoys adaptive security in the QROM and practically outperforms all existing adaptively secure DPRF constructions in terms of online evaluation time. We present experimental evaluations demonstrating that EQuADiSE achieves higher online throughput than all prior realizations of DiSE, including quantum-broken realizations based on discrete log-hard groups.

@misc{cryptoeprint:2026/799,
      author = {Sayani Sinha and Sikhar Patranabis and Debdeep Mukhopadhyay},
      title = {{EQuADiSE}: Efficient Quantum-safe Adaptive Distributed Symmetric-key Encryption},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/799},
      year = {2026},
      url = {https://eprint.iacr.org/2026/799}
}