Paper 2026/1174

A Layered Risk Scoring Model for TLS Connections Against Quantum Threats

Abstract

The advancement of quantum computing threatens public-key cryptographic algorithms used in TLS connections, such as RSA and ECDHE. The Harvest Now, Decrypt Later (HNDL) attack exposes long-term confidential data to risk even before quantum computers are practically realized, yet a systematic methodology for immediately quantifying the quantum vulnerability of individual TLS connections remains absent. This paper proposes a layered risk scoring model that quantifies the quantum threat exposure of TLS connections on a 0–100 scale. The model decomposes risk into five independent layers—TLS protocol exposure (L1), legacy public-key vulnerability (L2a), AES-128 Grover weakening (L2b), PQC Level-1 vulnerability (L2c), and certificate expiration urgency (L3)—and incorporates an HNDL global multiplier M that reflects the confidentiality retention period of transmitted data. Applied to 502 real-world TLS sessions across four industry sectors with M = 1.50, the domestic average risk score (16.0) is approximately 34% higher than the global average (11.9), with domestic legacy key exchange usage at 77.4% versus 53.5% globally and PQC adoption at 22.6% versus 46.5%. These results quantitatively confirm the elevated quantum risk of domestic network infrastructure, underscoring the urgency of PQC transition.