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crt.sh
Certificate transparency log search engine for monitoring SSL certificate issuance.
About
crt.sh operates as a comprehensive certificate transparency log search engine that provides free access to SSL/TLS certificate data from multiple Certificate Transparency (CT) logs. The platform aggregates certificate information from various CT log sources, creating a centralized database for security research and monitoring purposes.
The search engine enables users to query certificates by domain name, organization, certificate authority, or specific certificate attributes. Security professionals can track certificate issuance patterns, identify unauthorized certificates, and monitor subdomain discovery through comprehensive search capabilities. The platform displays detailed certificate information including validity periods, certificate authorities, and associated domain names.
What distinguishes crt.sh is its completely free access model and extensive historical data coverage spanning multiple years of certificate transparency logs. The service provides both web-based search interfaces and API endpoints for automated queries. Advanced search operators allow filtering by certificate types, issuance dates, and specific certificate authorities.
Security researchers, penetration testers, and IT security teams utilize crt.sh for various reconnaissance and monitoring activities. Common use cases include:
- Subdomain enumeration during security assessments
- Monitoring for unauthorized certificate issuance
- Certificate inventory management and compliance tracking
- Brand protection and domain monitoring initiatives
- Threat intelligence gathering and infrastructure mapping
The platform supports bulk domain monitoring through its API, enabling organizations to integrate certificate transparency monitoring into their security workflows. Security teams can automate alerts for new certificate issuance affecting their domains or brands.
crt.sh serves as an essential tool in the broader certificate transparency ecosystem, supporting industry efforts to improve SSL/TLS certificate security and transparency. The service complements other security monitoring tools by providing visibility into the public certificate infrastructure that underpins web security.