auditing-tls-certificate-transparency-logs

name	auditing-tls-certificate-transparency-logs
description	Monitors Certificate Transparency (CT) logs to detect unauthorized certificate issuance, discover subdomains via CT data, and alert on suspicious certificate activity for owned domains. Uses the crt.sh API and direct CT log querying based on RFC 6962 to build continuous monitoring pipelines that catch rogue certificates, track CA behavior, and map the external attack surface. Use when working with auditing tls certificate transparency logs.
domain	cybersecurity
tags	["certificate-transparency","CT-logs","crt-sh","subdomain-discovery","TLS-monitoring","RFC-6962"]
subdomain	threat-intelligence
version	1.0.0
author	oyi77
license	Apache-2.0
nist_csf	["ID.RA-01","ID.RA-05","DE.CM-01","DE.AE-02"]

Auditing Tls Certificate Transparency Logs

Overview

Cybersecurity skill for auditing tls certificate transparency logs. Follows industry best practices and security standards.

When to Use

Trigger phrases:

• "auditing tls certificate transparency logs"

• "Monitors Certificate Transparency (CT) logs to detect unauthorized certificate i"

• Monitoring owned domains for unauthorized or unexpected certificate issuance by unknown Certificate Authorities

• Discovering subdomains and hidden services through certificates logged in public CT logs

• Detecting phishing infrastructure that uses look-alike domain certificates (typosquatting, homograph attacks)

• Auditing Certificate Authority compliance by verifying all issued certificates appear in CT logs as required by browser policies

• Building continuous certificate monitoring into a security operations pipeline with alerting for new issuances

Do not use for attacking or disrupting Certificate Authorities, for scraping CT logs in violation of rate limits or terms of service, or as the sole method of subdomain enumeration without corroborating results through DNS verification.

When NOT to Use

• When you lack proper authorization for testing
• For production systems without change management
• When the task requires legal or compliance expertise beyond technical scope

Prerequisites

• Python 3.10+ with requests, cryptography, and pyOpenSSL libraries installed
• Network access to crt.sh (HTTPS) and public CT log servers
• A list of domains to monitor (owned domains, brand variations, typosquat candidates)
• SMTP credentials or webhook URL for alerting on new certificate discoveries
• Basic understanding of X.509 certificate structure and TLS certificate chain validation

Workflow

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": ,
}

 () -> :
     {k: re.findall(v, text)  k, v  IOC_PATTERNS.items()}