Paper 2026/2087

Batched and Weighted Threshold Encryption with Silent Setup

Abstract

Batched Threshold Encryption (BTE) enables a committee of parties to jointly decrypt any subset of ciphertexts from a large set, while all other ciphertexts remain private. BTE has applications in blockchains, particularly in designing encrypted mempools, where transactions are encrypted until included into a block to prevent maximal extractable value (MEV) attacks. Existing BTE constructions, however, encounter one of the following usability downsides: (a) reliance on expensive distributed key generation (DKG) protocols, (b) dependency on a batch label during ciphertext generation, (c) ciphertexts that are only decryptable if they are encoded with respect to a non-conflicting index in the batch, or (d) no support for weighted threshold policies. In this work, we present a BTE scheme that simultaneously addresses all of the above issues. It has a silent setup (key generation does not require interaction between parties), is batch and index independent, and supports weighted threshold policies. Our construction is based on prime-order groups with bilinear pairings with security proof in the Generic Group Model. Our ciphertext size is also the shortest among existing silent batched threshold encryption schemes with only $2$ group elements in addition to the message length.