Google Brings Quantum-Hardened HTTPS To Chrome In Major Security Upgrade

Traditional cryptographic signatures that underpin HTTPS can be broken by a sufficiently powerful quantum computer using algorithms like Shor's, threatening the trust model of secure connections. To help protect against this threat, Google is rolling out a major upgrade to Secure HTTP in its Chrome browser. In a blog post published yesterday, the Chrome Secure Web and Networking Team outlined a new program to make TLS certificates resistant to future quantum attacks without imposing significant performance penalties on the web ecosystem.

The central innovation in Google's approach is the adoption of Merkle Tree Certificates (MTCs), a structure that replaces the long chain of signatures found in classic X.509 certificates with compact proofs that a given certificate is included in a public Merkle tree. Under this model, a Certification Authority signs a single "Tree Head" representing "potentially millions of certificates," and the browser verifies inclusion using a lightweight proof rather than downloading bulky cryptographic material. This cuts down the data sent during a TLS handshake while maintaining verifiable trust.

Post-quantum cryptographic algorithms such as ML-DSA (and others standardized by NIST, the National Institute of Standards and Technology) generate signatures and keys that are orders of magnitude larger than classical equivalents. Embedding these larger primitives directly in every HTTPS certificate would balloon certificate sizes from the current ~64-byte footprint to multiple kilobytes, drastically slowing connections and increasing bandwidth use. Merkle Tree proofs sidestep this by decoupling the size of strong cryptography from in-flight handshake data, keeping performance closer to today's web.

Google has already integrated preliminary MTC support into Chrome and is conducting feasibility studies with partners such as Cloudflare in a phased rollout. In the first phase, MTC-enabled connections are backed by traditional certificates to ensure a safe fallback while measuring real-world performance and reliability. The plan calls for broader bootstrapping with Certificate Transparency log operators and the eventual establishment of a Chrome Quantum-resistant Root Store alongside the existing root program by 2027.

This effort is part of a broader industry push to harden internet security ahead of quantum computing's maturation, with groups like the IETF's PKI, Logs, And Tree Signatures (PLANTS) working on standards for these new certificate paradigms. By investing early in scalable quantum-safe TLS mechanisms, Google aims to future-proof critical web trust infrastructure without fracturing compatibility or degrading performance. If only every development team were so dedicated.