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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:
X25519MLKEM768
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In the same announcement, Let's Encrypt said it plans to offer a staging environment for MTC issuance in late 2026 and aims for a production-ready deployment in 2027. It also said it will continue standards work and ecosystem tracking around MTCs and ML-DSA support.
On June 3, 2026, Let's Encrypt announced that it will pursue Merkle Tree Certificates as its preferred approach for post-quantum-safe Web PKI authentication, citing the impractical size of conventional post-quantum signatures such as ML-DSA in standard TLS handshakes. The announcement said nothing changes immediately for current users and emphasized that hybrid post-quantum key exchange remains the more urgent near-term priority.
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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
IETF RFC `10024` establishes three hybrid post-quantum TLS 1.3 key-agreement groups that combine ML-KEM with elliptic-curve Diffie-Hellman. `X25519MLKEM768` is the only group designated **Recommended** in IANA’s TLS Supported Groups registry; NIST-curve variants remain available for compliance-focused deployments. The standard formalizes an approach already used by browsers, CDNs, and TLS libraries and discourages use of earlier Kyber768 draft code points, reducing a standards barrier to mitigating harvest-now-decrypt-later exposure. Cloudflare has deployed Automatic Key Exchange to probe origin-server capabilities and select the strongest mutually supported TLS 1.3 group, prioritizing `X25519MLKEM768`. The rollout increased post-quantum traffic across scanned origins from roughly 25 billion to 45 billion daily connections, with 99.2% of post-quantum handshakes completing in one network round trip; retry-dependent handshakes fell from about 52% to 3.7%, cutting 90th-percentile handshake latency by more than 150 ms. Organizations still need origins that support `X25519MLKEM768` to receive end-to-end hybrid key-establishment protection, while post-quantum TLS authentication remains constrained by limited public WebPKI support for ML-DSA certificates and trusted roots.
Sep 13, 2026
Cloudflare has added post-quantum authentication to **Authenticated Origin Pulls** and **Custom Origin Trust Store**, enabling customers to use **ML-DSA** signatures for Cloudflare-to-origin TLS and build fully post-quantum-secure mutual TLS on that link. The company said the protection is effective only if organizations also remove trust in classical authentication paths to avoid downgrade attacks, and positioned the release as a key step toward its stated goal of full post-quantum security by 2029. Cloudflare also noted that post-quantum authentication for browser-facing WebPKI traffic will follow a different approach based on **Merkle Tree Certificates**. The rollout comes amid broader industry acceleration toward quantum-safe security. Cloudflare Radar has been tracking worldwide post-quantum encryption adoption, while Microsoft said the timeline for quantum risk is shifting and urged faster migration planning. Cloudflare said the new capability required changes across its Go-based control plane and **Pingora Origin** data plane, and disclosed that a **BoringSSL** upgrade triggered a June 10, 2026 incident when stricter `KeyUsage` enforcement caused compatibility problems before the issue was patched and resolved.
Jul 29, 2026