Paper 2026/605

Adaptively-Secure Proxy Re-Encryption with Tight Security

Shuo Chen, Shandong University

Shuai Han, Shanghai Jiao Tong University

Abstract

(Bi-Directional) Proxy Re-Encryption ($\mathsf{PRE}$) is a public-key encryption scheme that allows a proxy, holding a re-encryption key from $i$ to $j$, to transform a ciphertext intended for $i$ into one intended for $j$. $\mathsf{PRE}$ has numerous applications, including secure data sharing and cloud computing. However, most existing $\mathsf{PRE}$ schemes experience significant security degradation when adversaries are allowed to adaptively corrupt re-encryption or secret keys. Prior to this work, only a few $\mathsf{PRE}$ schemes achieved quasi-polynomial security loss in the adaptive setting, and even those were limited to restricted re-encryption strategies. In this paper, we propose four distinct $\mathsf{PRE}$ schemes with tight security guarantees in the adaptive setting, based on the $\mathsf{MDDH}$ assumption: - $\mathsf{PRE}_0$, $\mathsf{PRE}_1$: Single- and multi-challenge $\mathsf{aHRA}$-secure $\mathsf{PRE}$ schemes with tight security focusing on efficient constructions. - $\mathsf{PRE}_2$, $\mathsf{PRE}_3$: Single- and multi-challenge $\mathsf{aCCA}$-secure $\mathsf{PRE}$ schemes with (almost) tight security focusing on $\mathsf{CCA}$-type security. To achieve tightly $\mathsf{CCA}$-secure $\mathsf{PRE}$ schemes, we introduce a novel concept called tag-based language-malleable $\mathsf{NIZK}$ with special simulation soundness. This primitive provides simulation-sound $\mathsf{NIZK}$ while preserving a restricted form of malleability. We construct both one-time and unbounded versions of this primitive under the $\mathsf{MDDH}$(Matrix Decisional Diffie-Hellman) assumption.

@misc{cryptoeprint:2026/605,
      author = {Chen Qian and Shuo Chen and Shuai Han},
      title = {Adaptively-Secure Proxy Re-Encryption with Tight Security},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/605},
      year = {2026},
      url = {https://eprint.iacr.org/2026/605}
}