Paper 2026/1197

VOBE: Verifiable Outsourced Batched Encryption for Secure Delegation of Batched Decryption

Abstract

Batched encryption (BE) has emerged as a novel public-key cryptographic paradigm that enables the efficient decryption of a designated batch of $B$ ciphertexts simultaneously. By incorporating threshold decryption capabilities into this framework, batched threshold encryption (BTE) further decentralizes the decryption process. While both BE and BTE serve as highly effective solutions for mitigating Miner Extractable Value (MEV) attacks in blockchain networks by providing robust mempool privacy, ciphertext integrity, and communication efficiency, they still suffer from heavy computational overhead during the ciphertext decryption phase. In this paper, we address this computational bottleneck by introducing a novel framework that delegates the heavy decryption workloads to an untrusted cloud server while enabling verifiability of the outsourced computations. To achieve this, we first propose an outsourced batched identity-based encryption (O-BIBE) scheme by integrating outsourcing functionalities into the conventional BIBE paradigm, accompanied by a rigorous security proof. We then construct a verifiable outsourced batched encryption (VOBE) scheme by strategically combining O-BIBE with other core cryptographic building blocks and formally prove its security. To eliminate the single point of failure and enhance threshold resiliency, we extend our framework to the threshold setting by developing an outsourced threshold batched identity-based encryption (O-TBIBE) scheme. Building upon this, we propose a verifiable outsourced batched threshold encryption (VOBTE) scheme, which successfully achieves decentralized threshold resilience. Our proposed VOBE and VOBTE schemes are the first to concurrently guarantee ciphertext integrity and mempool privacy against sophisticated blockchain attacks, while significantly reducing decryption costs via efficient and verifiable outsourcing.

Note: Editorial revisions, notation alignment, and typo corrections for enhanced readability.