Paper 2026/1965

Lattice-based Threshold Traitor Tracing with Public Traceability

Abstract

Since the introduction of Threshold Traitor Tracing by Boneh, Partap and Rotem at CRYPTO '24, several works have extended the functionalities within the framework or improved the parameters. However, most of the existing solution fall short in providing post quantum security guarantees. The only lattice-based construction, due to Das et al. from EUROCRYPT '26, achieves post-quantum security but is limited to private tracing: a dedicated tracing authority holds a secret tracing key. In a threshold system, where the fundamental goal is to distribute trust, such a single point of failure is undesirable. In this work, we construct the first threshold traitor tracing scheme that simultaneously achieves post-quantum security and public traceability, where anyone can trace a pirate decoder without any secret tracing key. Our core building block is a Q-Partite Threshold Public Key Encryption (QTPKE) scheme, which is known to imply threshold traitor tracing when combined with a robust IPP code: we build QTPKE from plain Learning With Errors (LWE) using a key-shifting mechanism on top of Regev's encryption scheme thresholdised via {0,1}-Linear Secret Sharing. We finally prove the security of our scheme in the standard model under standard lattice assumptions.