SSL/TLS Certificates: A Practical Guide

Everything you need to know to properly encrypt your website communications

9 min

SSL/TLS certificates are the foundation of web encryption. Without them, any data travelling between a user’s browser and your server — passwords, payment details, personal information — can be intercepted by third parties. HTTPS, which relies on these certificates, is now a mandatory standard.

This guide explains how SSL/TLS works, what types of certificate exist, how to get a free one through Let’s Encrypt and what to do when configuration or renewal goes wrong.

How does SSL/TLS work?

SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) are cryptographic protocols that establish a secure channel between two parties. When a user visits an HTTPS site, a handshake occurs: the server presents its certificate, the browser verifies it against a certificate authority (CA) and both agree on a session key to encrypt communication.

The digital certificate contains the server’s public key, the domain identity and the signature of the issuing CA. TLS 1.3, the current version, has simplified the handshake to a single round-trip, improving both performance and security simultaneously.

Certificate types: DV, OV and EV

Not all SSL/TLS certificates are the same. They differ by the level of validation the certificate authority performs before issuing them, which affects both cost and the trust they convey.

  • Domain Validation (DV): validates only that you control the domain. The fastest and most affordable option, ideal for blogs and informational sites. Let’s Encrypt issues free DV certificates.
  • Organisation Validation (OV): the CA also verifies the legal existence of the organisation. Provides greater confidence for corporate websites.
  • Extended Validation (EV): thorough validation of business identity. Previously displayed a green bar in browsers; today it adds value in regulated sectors like banking or healthcare.

Let’s Encrypt and free certificates

Let’s Encrypt revolutionised the SSL/TLS ecosystem by offering free, automated DV certificates. Founded by the ISRG (Internet Security Research Group) and backed by Mozilla, Google and others, it issues over 300 million active certificates.

The Certbot tool automates certificate issuance and renewal. It integrates with Apache, Nginx and most web servers. Let’s Encrypt certificates are valid for 90 days, which forces automated renewal — a recommended security practice.

Correct SSL/TLS configuration

Installing a certificate is only the first step. Incorrect configuration can negate the protection SSL/TLS is supposed to provide. The most common mistakes include using obsolete protocol versions, weak cipher suites or not applying HSTS.

  • Disable SSL 2.0, SSL 3.0 and TLS 1.0/1.1: only TLS 1.2 and 1.3 are considered secure
  • Configure modern cipher suites: prioritise ECDHE with AES-GCM
  • Enable HSTS with a minimum max-age of one year and includeSubDomains
  • Implement OCSP Stapling to validate certificate status without relying on the CA in real time
  • Use tools like SSL Labs Server Test to verify your configuration

Renewal and automation

An expired certificate triggers browser errors that drive users away and break trust. Renewal should be fully automated. Certbot and most hosting panels (cPanel, Plesk) support automatic renewal.

Set up monitoring alerts that notify you at least 14 days before expiration. Services like UptimeRobot, Datadog or even simple cron scripts can verify certificate validity and alert you to any anomaly.

Common issues and how to fix them

SSL/TLS errors usually have specific causes and clear solutions. Diagnosing correctly saves hours of frustration and prevents incorrect fixes like disabling certificate verification.

  • ERR_CERT_DATE_INVALID: expired certificate — renew immediately
  • Mixed content: HTTP resources on an HTTPS page — update all URLs to HTTPS
  • ERR_CERT_COMMON_NAME_INVALID: domain does not match the certificate — issue one with the correct domain or use a wildcard
  • Incomplete chain of trust: missing intermediate certificate — configure it alongside the primary certificate

Key Takeaways

  • TLS 1.3 is the current standard: disable all versions prior to TLS 1.2
  • Let’s Encrypt provides free DV certificates with automatable renewal
  • Proper configuration (HSTS, cipher suites, OCSP) is as important as the certificate itself
  • Always automate renewal and monitor expiration with alerts
  • Diagnose errors with SSL Labs Server Test before making changes

Is your SSL certificate properly configured?

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