Encrypted clones can leak: Classification of informative subsets in Quantum Encrypted Cloning

TL;DR

This paper analyzes the information leakage in quantum encrypted cloning, revealing that certain subsets of stored clones can retain partial input information, thus exposing a structural confidentiality limitation.

Contribution

It classifies subsets of encrypted clones into different informational categories and characterizes when residual input dependence occurs, highlighting a leakage pattern.

Findings

Intermediate non-authorized subsets may retain residual input dependence.

Leakage pattern is parity-dependent, indicating structural confidentiality limits.

Classifies subsets into authorized, non-informative, and partially informative.

Abstract

Encrypted cloning enables the redundant storage of an unknown qubit while remaining compatible with the no-cloning theorem, since only one clone can later be recovered through key-consuming decryption. Because encryption in this protocol is introduced to enable cloning-compatible redundancy rather than to guarantee confidentiality by design, its secrecy properties must be assessed explicitly. Here we classify the subsets of the encrypted-clone storage register into authorized, completely non-informative, and partially informative sets. We show that intermediate non-authorized subsets may retain only a restricted residual dependence on the input state, and we characterize exactly when this dependence occurs. The resulting leakage pattern is parity-dependent, revealing a structural confidentiality limitation of encrypted cloning.