SSL & Domain Security Learning Center
Expert guides on SSL certificates, TLS security, DNS, DNSSEC, DMARC, and domain monitoring — written for developers, sysadmins, and security teams.
Featured Guides
Understand how SSL and TLS work, the difference between them, and why every website needs a valid certificate.
A clear technical explanation of the TLS handshake, asymmetric encryption, certificate chains, and OCSP revocation.
Learn how to get and install free, trusted SSL/TLS certificates from Let's Encrypt using Certbot for Apache, Nginx, and more.
Why SSL/TLS is mandatory for e-commerce, how it supports PCI DSS compliance, and best practices for securing an online store.
More Articles
A deep dive into what changed between TLS 1.2 and 1.3 — including performance improvements and security enhancements.
Five methods to check which TLS version a website supports: OpenSSL, curl, nmap, browser DevTools, and online tools.
Practical steps, automation strategies, and monitoring tools to ensure your SSL certificates never expire unexpectedly.
Understand every certificate type — validation levels, scope, cost, and which one is right for your specific use case.
A detailed comparison of Wildcard and Multi-Domain (SAN) SSL certificates to help you choose the right one.
Learn how CAs form the backbone of internet trust, how the chain of trust works, and how to choose the right CA.
Understand how CT logs work, how to search them for your domain, and how to get alerted when new certs are issued.
Understand HPKP's deprecated legacy, mobile app pinning strategies, and when pinning still makes sense today.
Learn how DNSSEC works, how to verify it, and why it is critical protection against DNS spoofing and cache poisoning.
Understand what DNS propagation is, why it isn't instantaneous, and how TTL and caching affect how long changes take.
How DANE uses DNSSEC to bind certificates directly to DNS, closing the gap left by the CA trust model.
Diagnose and fix ERR_SSL_PROTOCOL_ERROR in Chrome and other browsers — TLS mismatches, expired certs, and client-side causes.
Understand SSL modes (Full vs Strict), use Cloudflare Origin CA, and permanently fix invalid certificate errors.
All causes covered: cipher mismatch, TLS version conflicts, certificate validation failures, SNI issues, and firewalls.
Learn what breaks chain validation, why mobile apps are more sensitive, and how to build a complete chain.
Troubleshoot ACME challenges, port 80 issues, DNS problems, rate limits, and permission errors.
Why browsers block mixed content, how to detect it, and step-by-step fixes for WordPress, React, and server configs.
Step-by-step guide covering Certbot, DNS-01 wildcard certs, Kubernetes cert-manager, and cloud-managed certificates.
Integrate certificate health into CI/CD pipelines, Prometheus alerting, Kubernetes, Terraform, and incident runbooks.
What happens when a domain expires, real-world incidents, and how to set up a reliable multi-channel alert system.
From HSTS to certificate pinning — the complete guide to implementing HTTPS correctly and securely.
Complete implementation guide for all major security headers — with Nginx, Apache, and Next.js configuration examples.
Go beyond the basics — COOP, COEP, CORP, Trusted Types, and other advanced isolation headers explained.
How to migrate without losing SEO rankings — covering certificates, 301 redirects, HSTS, and post-migration monitoring.
How strong SSL/TLS practice maps onto ISO/IEC 27001 requirements for an Information Security Management System.
Looking for a specific header rather than a guide? The HTTP security headers reference documents each one — what to send, what it breaks, and what browsers actually do with it.
Stop reading about outages. Prevent them.
CertNotify checks your SSL certificates and domains once a day and emails you before either expires, and on paid plans it checks your DNS records daily too.