Cloudflare Develops Public Certificate Authority for Post-Quantum Web Security
Cloudflare introduces Merkle Tree Certificates to address post-quantum cryptographic scaling challenges for web infrastructure.
1Post-Quantum Security Challenges
Post-quantum cryptography introduces significant scaling hurdles for the current Web Public Key Infrastructure. Cloudflare reports that post-quantum signatures can be approximately 40 times larger than traditional classical signatures. This increase in size creates substantial bandwidth and storage requirements, necessitating new methods to maintain efficient web security and TLS handshake performance.
2Merkle Tree Certificate Innovation
Cloudflare tested Merkle Tree Certificates as an alternative to traditional certificate chains. By batching certificate data into an append-only Merkle tree, the system allows clients to verify certificates using compact inclusion proofs. This approach eliminates the need to transmit full certificate chains, resulting in a 9% faster median performance during experiments.
3Experimental Results and Deployment
The experiment involved serving billions of Merkle Tree Certificates to 50% of Chrome Beta 146 users for specific domains. Cloudflare concluded this testing phase in August 2026. The company is now developing a public certificate authority that supports this issuance method, aiming for integration into Chrome's quantum-resistant Root Store by early 2027.
4Landmark-Based Verification Mechanism
To further optimize TLS handshakes, Cloudflare utilizes landmark-based verification. The system distributes authenticated landmarks to clients, which then verify certificate inclusion via cryptographic proofs. In standard scenarios, this handshake transmits one public key, one signature, and an inclusion proof smaller than 1 KB, significantly reducing the total data transferred during connection.
5Transparency and Log Integrity
Cloudflare integrates certificate issuance with transparency logging to ensure security. An independent mirroring cosigner verifies and stores updated tree states to detect inconsistent log views. This mechanism helps preserve issuance records if the original log becomes unavailable, ensuring the system remains robust even if individual components experience downtime or data access issues.
6Operational Fallback Requirements
Because clients may be newly installed, offline, or missing recent landmark updates, servers must retain a standalone certificate as a fallback. This ensures that connectivity is maintained even when the optimized Merkle Tree Certificate path is unavailable. Cloudflare emphasizes that browser support and a diverse ecosystem of cosigners remain essential for deployment.
7Industry Concerns on Revocation
Experts have raised questions regarding revocation and incident handling within this new framework. Alicja Tendaj of SSL.com noted that with trust anchored in a tree head and short validity periods, traditional methods like OCSP and CRL require re-evaluation. The industry must determine how quickly a certificate can be effectively removed from the tree.
8Future Path for Trust
Cloudflare's planned public certificate authority requires rigorous evaluation before its issuance can be trusted through Chrome's quantum-resistant Root Store. Production deployment will be critical to determine if this approach can maintain transparency, interoperability, and availability at Internet scale. The company continues to coordinate these security upgrades to protect against future quantum threats.