TSitH: Threshold Signatures in the Head

"Preview Talk" (by team TSitH) @ TCPT3, in reply to the NIST Threshold Call

Abstract: In this talk, we will introduce a family of threshold signature schemes based on the MPC-in-the-Head paradigm with threshold-friendly Merkle-tree commitments. It builds on the recent Threshold-Signatures-in-the-Head (TSitH) framework which enables the construction of threshold signatures from any one-way function. The submission will include three concrete instantiations of the framework, based respectively on the block cipher AES, the multivariate quadratic problem (MQ), and the syndrome decoding problem (SD). These variants are intended to provide plausibly post-quantum security: no efficient quantum or classical attacks are known against the underlying symmetric primitives used in the MPC-in-the-Head construction, nor against the hard problems on which the three instantiations rely. The TSitH framework was introduced as a preprint in mid-2026. The present submission aims to develop that framework into concrete threshold signature schemes suitable for consideration in the NIST MPTC process. These schemes combine techniques from hash-based proof systems (MPC-in-the-Head with Merkle tree commitments) and generic secure multiparty computation in order to obtain practical threshold signatures schemes based on various security assumptions.

Joint work: Thibauld Feneuil, Matthieu Rivain, Damien Vergnaud, Auguste Warmé-Janville.

Suggested readings

• Preview Writeup (PDF): TSitH: Threshold Signatures in the Head: A framework for threshold MPC-in-the-Head signatures
• “Threshold Signatures in the Head” (ia.cr/2026/1125)
• Threshold computation in the head: Improved framework for post-quantum signatures and zero-knowledge arguments (ia.cr/2023/1573)