In a bid to enhance online security, Google has embarked on a mission to make HTTPS certificates quantum-resistant without compromising browser performance. This initiative addresses the challenge posed by quantum-resistant cryptographic materials, which are substantially larger than current X.509 certificates. The traditional X.509 certificate is approximately 64 bytes, while the quantum-resistant equivalent requires around 2.5 kilobytes. Implementing these larger certificates directly would significantly slow down TLS handshakes.
To overcome this, Google is employing Merkle Tree Certificates (MTCs), a novel data structure that compresses the quantum-resistant cryptographic material. With MTCs, a Certificate Authority (CA) only needs to sign a single ‘Tree Head,’ which represents millions of certificates. This allows browsers to receive a compact proof of inclusion instead of retrieving and processing the entire certificate chain. This approach reduces bandwidth overhead and maintains efficient browser operations.
This effort is being rolled out in collaboration with Cloudflare and is already gaining traction with integration in Google Chrome. The initiative is being standardized by the IETF PLANTS working group, and it shifts from traditional X.509 certificate chains to the more compact Merkle Tree proofs. These proofs inherently support post-quantum algorithms and incorporate certificate transparency as a built-in property, rather than an add-on.
Google’s rollout plan consists of three phases:
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<li>Phase 1 (currently ongoing): A feasibility study with Cloudflare using real traffic, supported by an X.509 fallback.</li>
<li>Phase 2 (Q1 2027): This phase invites existing Certificate Transparency log operators to establish public MTC infrastructure.</li>
<li>Phase 3 (Q3 2027): The launch of the Chrome Quantum-resistant Root Store (CQRS) with optional opt-in downgrade protections.</li>
</ul>
Moreover, Chrome seeks to implement new Public Key Infrastructure (PKI) policy principles, which include ACME-only workflows, modern revocation mechanisms, reproducible domain control validation, and continuous external monitoring to replace traditional annual audits.
This phased approach aims to cultivate a robust, efficient quantum-safe HTTPS ecosystem, paving the way for enhanced internet security in the face of emerging quantum computing capabilities.

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Google is working to make HTTPS certificates quantum-resistant without degrading browser performance. The core challenge is that post-quantum cryptographic materials are far larger than traditional X.509 certificates (~2.5KB vs ~64 bytes), which would slow TLS handshakes. To address this, Google is adopting Merkle Tree Certificates (MTCs), where a Certificate Authority signs a single Tree Head representing millions of certificates, allowing browsers to receive compact inclusion proofs instead of full certificate chains. The initiative is being developed with Cloudflare, standardized by the IETF PLANTS working group, and integrated into Chrome. A three-phase rollout is planned: a current feasibility study with Cloudflare, public MTC infrastructure in Q1 2027, and the Chrome Quantum-resistant Root Store (CQRS) launch in Q3 2027. New PKI policy principles including ACME-only workflows and modern revocation mechanisms are also planned.

Google's Initiative for Quantum-Resistant HTTPS