KEEPING THE INTERNET FAST AND SECURE: INTRODUCING MERKLE TREE CERTIFICATES

Summary from the TLDR InfoSec newsletter

Cloudflare and Chrome are testing Merkle Tree Certificates (MTCs) to improve post-quantum signature performance, which are 20 times larger than current ECDSA signatures (ML-DSA-44 signatures are 2,420 bytes vs 64 bytes for ECDSA-P256). MTCs reduce TLS handshakes to one signature, one public key, and one Merkle inclusion proof by batching certificates into Merkle trees with signed tree heads sent out-of-band to clients, compared to today's five signatures and two public keys per handshake. The deployment will use "bootstrap certificates" from trusted CAs to validate MTCs via certificate transparency, starting early 2026 with some Cloudflare and Chrome users to assess performance and ossification issues.