Mind the Gap: Policy vs Reality in Post-Quantum TLS Deployment

Abstract

Post-quantum cryptography (PQC) has evolved from a long-term planning concern into an operational priority. Following NIST's standardization of PQC, governments and standard bodies published transition roadmaps outlining migration timelines, priority sectors, and deployment strategies. However, our survey of these policies reveals substantial divergence in technical prescriptions and urgency. It remains unclear how widely PQC has been adopted in practice and how policy differences translate into observable deployment outcomes. To address this gap, we present the first longitudinal measurement study of post-quantum TLS (PQ-TLS) adoption. By establishing more than 2 billion TLS handshakes, we analyze cryptographic negotiation behavior across 1 million domains from 11 globally distributed vantage points. Despite varied policy guidance, we observe configuration convergence: PQ-TLS deployment overwhelmingly centers on a single hybrid construction, and much of the apparent progress is driven by managed infrastructure providers. National timelines and sectoral priorities show limited correspondence with observed deployment patterns. Contrary to early experimental studies suggesting measurable overhead, we find that PQ-TLS introduces no meaningful latency increase in Internet settings, although it is frequently deployed alongside legacy TLS configurations. Together, these findings highlight a gap between policy expectations and early deployment reality, and provide empirical insight to inform more grounded PQ-TLS transition.