CT Log Explorer Updates to v81.16 with Expanded Certificate Transparency Monitoring

Certificate Transparency (CT) logs form the backbone of web security by publicly recording all issued SSL/TLS certificates, enabling real-time monitoring for misissued or malicious certificates. The open-source CT Log Explorer tool, used by security teams to query and analyze these logs, has been updated to version 81.16 with significant operational changes.

This release indexes 75 distinct logs operated by eight organizations: Google (Argon/Xenon series), Cloudflare (Nimbus), DigiCert (Wyvern/Sphinx), Sectigo (Tiger/Elephant/Sabre/Mammoth), Let's Encrypt (Sycamore/Willow/Oak), TrustAsia (HETU/Luoshu), IPng Networks (Halloumi/Gouda), and Domain Domains. Each operator maintains multiple logs categorized by year and half-year identifiers (e.g., Argon2027h1 for Google's first-half 2027 log), reflecting a structured approach to log rotation and cryptographic epoch management.

Notably, the update includes two explicitly labeled "bogus" placeholder logs (one from IPng Networks, one unspecified) designed as compatibility shims. These simulate RFC 6962 log structures to prevent failures in older or non-compliant CT client libraries that crash when encountering unrecognized log formats—a pragmatic workaround for real-world ecosystem fragmentation.

For administrators, this consolidation means broader coverage for detecting certificate spoofing or CA breaches. Tools like crt.sh rely on such indexes to scan for fraudulent certificates across all major providers. However, the inclusion of placeholder logs underscores persistent interoperability challenges in CT adoption. Some enterprise systems still struggle with log diversity despite the protocol's 2013 standardization.

The update carries no functional enhancements to CT Log Explorer itself but ensures the tool references the current log ecosystem. Operators periodically retire logs (like Google's 2025-era Xenon logs) as cryptographic parameters evolve, making such index updates essential for comprehensive monitoring. Security teams should verify their CT monitoring systems align with this revised log list to maintain visibility.