Finite-Length Analysis of Operational Perfect Secrecy and Key-Length Trade-Offs: A Systematic Review of Security Implications and Risk Analysis

Abstract

Classical formulations of perfect secrecy rely on asymptotic assumptions that are incompatible with modern communication systems operating under strict resource constraints, such as quantum key distribution (QKD), ultra-reliable low-latency communication (URLLC), and emerging 6G networks. These limitations motivate finite-length security analysis, where secrecy must be evaluated under constrained key sizes, finite observations, and practical system conditions.This paper presents a systematic literature review of finite-length secrecy, focusing on operational perfect secrecy and key-length trade-offs across quantum and classical domains. The review synthesizes key frameworks, including entropy- based composable security, probabilistic leakage metrics, and finite blocklength information-theoretic models, and provides an integrated perspective on the inter- play between secrecy performance, reliability, and computational complexity. The findings show that finite-length constraints introduce unavoidable information leakage, probabilistic guarantees, and diminishing returns in keylength utilization. While metrics such as average information leakage and secrecy outage probability enable practical evaluation, their lack of standardization limits comparability. The paper identifies key research gaps and outlines directions toward unified, scalable, and practically deployable secrecy frameworks.