Certificate Transparency (CT) is a security framework that provides public logging and monitoring of SSL/TLS certificates. Here's what you need to know:

Key Points:

• CT logs are permanent, append-only records of SSL/TLS certificates maintained by various organizations
• Every public certificate must be logged in at least two CT logs for redundancy
• Records cannot be deleted or modified, only updated (e.g., for revocation status)
• Logs use Merkle trees for tamper-proof record-keeping

Main Benefits:

• Helps organizations monitor unauthorized certificates issued for their domains
• Enables oversight of Certificate Authority (CA) practices and quality
• Provides data for research on internet security trends
• Creates transparency in the public certificate ecosystem

Key Tools:

• crt.sh - Most popular tool for searching CT logs
• Censys - Alternative CT log search tool

Technical Implementation:

• Logs are divided into "shards" by time period
• Expired certificate shards become inactive but remain accessible
• High uptime and fast access speeds are required
• Must handle global logging requirements

Important Considerations:

• Private certificates are not logged in CT systems
• Some argue CT logs could reveal internal network information
• System operates through voluntary community participation
• No formal enforcement mechanism for maintaining logs

The CT system has proven effective at improving SSL/TLS certificate transparency and security across the internet through collaborative industry efforts.

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