Cloudflare Plans Merkle Tree Certificate Issuance for Post-Quantum Web PKI

Summary

Cloudflare plans MTC issuance through its new CA, targeting Chrome’s Quantum-resistant Root Store in early 2027. A Chrome Beta experiment served billions of MTCs and found landmark-relative certificates 9% faster at median, using classical signatures.

Key points

Cloudflare says its planned certificate authority will support Merkle Tree Certificate (MTC) issuance, with inclusion in Chrome’s Quantum-resistant Root Store targeted for early 2027; Chrome approval and evaluation are still required.
MTCs use an append-only Merkle tree and inclusion proofs to link certificates to a signed tree head, coupling certificate issuance with transparency logging.
Cloudflare’s Chrome Beta experiment served billions of MTCs to a selection of its domains; the test used classical signatures, not post-quantum signatures.
Cloudflare reports that landmark-relative MTCs were 9% faster at the median than a classical certificate chain in the experiment, noting that most of the benefit came from intermediate certificate elision.
Landmark-relative certificates can reduce handshake overhead by distributing signed tree information to clients out of band; standalone certificates remain a fallback for clients without relevant landmark updates.
Cloudflare says MTC logs can avoid per-certificate signatures and duplicate certificate entries, addressing the scaling burden it estimates could make post-quantum signatures increase Certificate Transparency log data by 40 times.

Article Details

Event Type: Cloudflare announced plans to support Merkle Tree Certificate issuance through its certificate authority and reported results from an MTC experiment with Chrome.
Impact: Cloudflare reported that its experiment served billions of MTCs to 50% of Chrome Beta 146 for selected Cloudflare domains. Landmark-relative MTCs were 9% faster at the median than a classical signature chain in the experiment, which used classical signatures. Cloudflare is targeting early 2027 for inclusion in Chrome’s Quantum-resistant Root Store; it must first apply and undergo evaluation. The article describes a planned post-quantum certificate issuance path, not a completed production deployment.

Vendors

Cloudflarehave emerged as the path forward. This year, after a successful experimental deployment with Chrome, Cloudflare is full steam ahead on MTCs.

Products

Google Chrome(MTCs) have emerged as the path forward. This year, after a successful experimental deployment with Chrome, Cloudflare is full steam ahead on MTCs.

Tools

AzulCloudflare will implement our mirroring cosigner in Azul, our open-source Rust-based transparency log, and for maximal interoperability, it will implement c2sp's tlog mirror protocol.Boulderdomain-control validation, and issuance workflows. Cloudflare's ACME infrastructure will be a fork of Boulder, the widely deployed and well-tested ACME software that powers Let's Encrypt. Let's Encrypt is actively