Dynamic Threshold Key Encapsulation With Transparent Setup

A threshold key encapsulation mechanism (TKEM) facilitates the secure distribution of session keys among multiple participants, allowing key recovery through a threshold number of shares. TKEM has gained significant attention, especially for decentralized systems, including blockchains. However, existing constructions often rely on trusted setups, which pose security risks such as a single point of failure and are limited by fixed participant numbers and thresholds. To overcome this issue, we propose a dynamic TKEM with a transparent setup, allowing for a flexible selection of both recipients and thresholds without relying on trusted third parties in the setup phase. In addition, our construction does not rely on pairing operations, which are less efficient compared to exponentiation. We prove the selective chosen-ciphertext security of our construction under the decisional Diffie-Hellman assumption, zero-knowledge, and soundness of a non-interactive zero-knowledge (NIZK) proof system. We also show that our scheme satisfies decapsulation consistency when the underlying NIZK system is sound. Our proof-of-concept implementation highlights the practicality and efficiency of this approach, further advancing the field of threshold cryptography.