Adamas: One-Round Lattice-Based Threshold KEM and PKE under Adaptive Corruptions

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

Abstract: In this talk, we present Adamas, a family of one-round lattice-based (t,N)-threshold key encapsulation mechanism (TKEM) and public key encryption (TPKE) schemes.  It comprises two TKEM schemes and one TPKE scheme, all supporting one-round decryption, and achieving chosen-ciphertext (CCA) security under adaptive corruptions, based on standard structured-lattice assumptions with polynomial modulus.  For active security, our TKEM schemes TKEM₁ and TKEM₂ achieve security-with-abort while our TPKE scheme achieves stronger robustness.  Technically, all our schemes are threshold variants of Regev-style encryption schemes augmented with non-interactive zero-knowledge (NIZK) proofs.  Our TKEM₁ uses Shamir secret sharing and supports synchronous decryption for large-scale parties.  Our TKEM₂ and TPKE use replicated secret sharing, and support asynchronous decryption for small-scale parties.  We use the polynomial flooding technique and the masking technique to control leakage about the secret key revealed by partial-decryption queries while keeping the modulus polynomial.  More precisely, TKEM₁ combines the masking technique and adaptive Hint-MLWE assumption, whereas TKEM₂ and TPKE rely on a new adaptive leftover hash lemma under noisy linear leakage.  We use the Fujisaki-Okamoto transform to achieve security-with-abort in the threshold setting for our TKEM schemes, and use NIZK proofs to achieve stronger robustness for our TPKE scheme.  Finally, we provide a concrete efficiency estimate and comparison with prior works.  To our best knowledge, Adamas is the first lattice-based TKEM/TPKE family enjoying security under adaptive corruptions and polynomial modulus, simultaneously.

Joint work: Shuai Han, Shengli Liu, Yuxin Zhang, Yunxiao Zhou.

Suggested readings

• Preview Writeup (PDF): Adamas: One-Round Lattice-Based Threshold KEM and PKE under Adaptive Corruptions
• Adaptively CCA-Secure Threshold Decryption from Lattices with Polynomial Modulus (ia.cr/2026/1627)