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Cloudflare and Google are developing Merkle Tree Certificates (MTCs) to bring post-quantum resilience to WebPKI authentication without the impractically large TLS certificate chains produced by conventional quantum-safe signatures. Under the proposed design, a certificate authority adds certificates to an append-only Merkle tree, signs a checkpoint representing potentially millions of certificates, and supplies a compact inclusion proof; TLS handshake data is expected to remain near 40 KB. Certificate Transparency is built into issuance, with an independent mirror cosigning log state, aiming to reduce exposure to rogue certificates and forged transparency records.
Cloudflare is building a CA that will issue both conventional certificates and MTCs, using ACME and a fork of Boulder for validation and issuance, plus Azul and the C2SP tlog-mirror protocol for log mirroring. A Chrome Beta 146 experiment covering 50% of users and free-plan domains found landmark-based MTC handshakes had a 9% median speed improvement over classical chains, though it used classical signatures and benefited partly from removing an intermediate certificate. MTC remains an IETF PLANTS Internet-Draft, and Cloudflare must enter Chrome's Quantum-resistant Root Store before trusted production deployment; it plans initial issuance in Q1 2027 and advises continued Certificate Transparency monitoring for legacy certificates that could enable downgrade paths.
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The 2011 compromise of Dutch certificate authority DigiNotar enabled issuance of roughly 500 counterfeit certificates for Google and other websites. Some were used to surveil web users in Iran, helping spur certificate-transparency programs.
Cloudflare reported a deployment to 50% of Chrome Beta 146 users that issued billions of Merkle Tree Certificates for free-plan domains. Landmark-based handshakes showed a reported 9% median speed improvement over classical certificate chains, though the test used classical signatures and benefited partly from omitting an intermediate certificate.
Google announced a Merkle Trees-based approach intended to make WebPKI certificates resistant to future quantum attacks, avoiding the overhead of replacing every certificate-chain signature with a post-quantum signature.
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Google announced a new Chrome program to make HTTPS certificate authentication resilient to future quantum attacks by evolving Certificate Transparency (CT) toward **Merkle Tree Certificates (MTCs)**. The approach is designed to mitigate the risk that a sufficiently capable quantum computer running **Shor’s algorithm** could forge classical signatures used in today’s PKI/CT ecosystem (e.g., forging **Signed Certificate Timestamps** to make unlogged certificates appear valid). Rather than immediately adding post-quantum X.509 certificate chains into the **Chrome Root Store**, Google is pursuing MTCs through the IETF’s new **PLANTS** working group (*PKI, Logs, And Tree Signatures*), replacing heavyweight serialized signature chains with compact Merkle proofs of inclusion anchored by a CA-signed tree head. Google’s design combines classical and post-quantum cryptography (including **ML-DSA**) so an attacker would need to break both to successfully forge proofs, while keeping handshake/CT authentication data small. Ars Technica reports Google is using “clever math” to keep MTC-related authentication artifacts roughly **64 bytes** (similar to current CT proofs) despite post-quantum key and signature size growth, and that the system is already implemented in Chrome with **Cloudflare** enrolling roughly **1,000 TLS certificates** to test MTC behavior; Cloudflare is currently generating the distributed ledger, with a plan for CAs to eventually assume that role.
Aug 4, 2026
Let's Encrypt said it will use **Merkle Tree Certificates (MTCs)** as its preferred approach for post-quantum authentication on the public web, arguing that conventional post-quantum signatures such as `ML-DSA` would make standard TLS certificate chains too large for reliable internet-scale handshakes. The model batches certificate issuance under a single signed Merkle tree head and delivers compact inclusion proofs, reducing handshake overhead while making Certificate Transparency inherent to issuance. Let’s Encrypt said current subscribers do not need to take immediate action, but future ACME clients and related tooling will need updates as the ecosystem moves toward the new format. The move aligns Let’s Encrypt with broader work by **Google, Cloudflare, Chrome, DigiCert, and the IETF**, as browser and infrastructure vendors push for scalable post-quantum TLS ahead of government migration deadlines from the NSA, NIST, and the EU. Let’s Encrypt plans a staging environment for MTC issuance in late 2026 and a production-ready deployment in 2027, while continuing to track `ML-DSA` support for traditional X.509 use cases outside the browser ecosystem. It also said the more urgent near-term defense remains post-quantum encryption against harvest-now-decrypt-later threats, urging operators to enable hybrid key exchange such as: ```text X25519MLKEM768 ```
Jun 29, 2026
Cloudflare has applied to the root programs operated by Google Chrome, Apple, Microsoft, and Mozilla to become a publicly trusted certificate authority (CA) capable of issuing TLS/X.509 certificates directly to customers. The company is also pursuing acquisition of an already trusted GlobalSign root certificate, reportedly **GlobalSign Root R5**, to enable certificate issuance before its own root is broadly embedded in client trust stores. Cloudflare plans to require certificate customers to use **ACME** automation and the ACME Renewal Information (**ARI**) extension, supporting automated certificate renewal, revocation, and reissuance. It also intends to begin experimental issuance of post-quantum Merkle-Tree Certificates (**MTCs**) alongside conventional certificates in 2026, expanding its role from CDN and security provider to public Web PKI operator.
Sep 30, 2026