Paper 2025/1721

Q-Stream: A Practical System for Operational Perfect Secrecy

Abstract

Information-theoretic security (ITS) offers the strongest known form of cryptographic protection, guaranteeing confidentiality even against adversaries with unbounded computational power. However, Shannon’s perfect secrecy theorem requires keys as long as the message, which has made ITS widely regarded as impractical for real-world deployment. This paper updates Q-Stream, introduced in prior work (“A Quantum-Safe Key-Distribution Mechanism having Non-Conjectured Hardness, while scalable for a Vernam Cipher, under Shannon Conditions,” Proceedings of the Future Technologies Conference (FTC 2025), Springer LNNS, Munich, 2025), the first practical system to achieve ITS under the framework of Operational Perfect Secrecy (OPS), having also been introduced in prior work. Q-Stream uses ephemeral public quantum-random blocks (Q-Blocks) combined with short secret defragmentation keys (DFKs) to produce one-time pads with provable OPS security levels. The system implements both Combinatorial ITS (C-ITS) and Dimensional Ambiguity ITS (DA-ITS) modes, providing tunable secrecy levels while drastically reducing the burden of key distribution. We describe Q-Stream’s architecture, protocol design, security analysis, and implementation, and evaluate its performance against conventional and post-quantum cryptography. Our results show that Q-Stream delivers high-throughput, low-latency encryption while providing provable information-theoretic confidentiality, demonstrating that OPS-based security is practical at scale.