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Android’s Certificate Transparency (CT) policy requires publicly trusted TLS certificates used by CT-enforcing applications to carry sufficient Signed Certificate Timestamps (SCTs) from qualifying, operator-diverse CT logs. Certificates valid for 180 days or less need two embedded SCTs from distinct logs and operators; longer-lived certificates need three. SCTs delivered through OCSP stapling or the TLS handshake require two SCTs from distinct operators.
Compliance is evaluated against Android’s CT log list, which is updated daily and reflects CT log lifecycle and policy status. CT enforcement is disabled if no log list is available or if the installed list is more than 70 days old, making reliable distribution of current log-state data essential for applications that enforce the policy.
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Google publishes a refreshed Android CT log list daily, and Android devices attempt to download the latest list daily for certificate verification. Android disables CT enforcement when no local list is available or when the available list is more than 70 days old.
Android's Certificate Transparency Policy requires publicly trusted TLS certificates to satisfy CT-compliance requirements when validated by CT-enforcing Android applications. Compliance depends on SCT quantity and delivery method, CT log status, and operator diversity.
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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
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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Google is adding platform-level **TLS Encrypted Client Hello (ECH)** support in Android 17, enabling compatible apps targeting the release to encrypt hostname metadata—including Server Name Indication (SNI)—during TLS handshakes. Used alongside Private DNS, ECH reduces ISPs’, Wi-Fi operators’, and other passive observers’ ability to identify websites and services users access; ECH GREASE will also generate cover traffic when a destination does not support ECH. The implementation follows RFC 9849, which standardizes ECH’s encryption of an inner ClientHello under a server public key and specifies anti-downgrade, retry, and denial-of-service safeguards. Android 17 will additionally require permission for app local-network discovery and connections, enable Certificate Transparency by default, and allow participating carriers to disable 2G automatically to reduce exposure to rogue base stations and SMS blasters.
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