What Is an SSL Certificate?

Category: Security & SSL · Updated 2026-10-30

An SSL certificate is a digital file that proves a website's identity and enables an encrypted HTTPS connection between the visitor's browser and the server. Today the protocol actually used is TLS, the successor of SSL, but the name "SSL certificate" has stayed. Free certificates are available from Let's Encrypt.

What SSL and TLS mean

SSL (Secure Sockets Layer) was the original encryption protocol for the web. It was replaced by TLS (Transport Layer Security), and versions TLS 1.2 and TLS 1.3 are the ones in use today. When people say "SSL certificate" they almost always mean a TLS certificate. A site that uses one loads over HTTPS on port 443 and shows a padlock in the browser.

What a certificate does

Encryption: data such as passwords and payment details cannot be read by anyone watching the network.
Authentication: the browser can check that it is talking to the real domain and not an impostor.
Integrity: content cannot be changed on the way without being detected.

The certificate contains the domain name, the public key, the issuing certificate authority (CA), and the validity dates. The browser checks that the CA is trusted, the domain matches and the certificate has not expired.

Types of SSL certificates

Type	What is verified	Typical use
Domain Validated (DV)	Control of the domain only	Blogs, small sites, most hosting plans
Organization Validated (OV)	Domain plus the organization's existence	Business sites
Extended Validation (EV)	Strict legal and identity checks	Banks, large enterprises
Wildcard	One certificate for all subdomains of a domain	Sites with many subdomains
Multi-domain (SAN)	Several different domains in one certificate	Companies with multiple sites

All types provide the same strength of encryption. They differ in how much identity checking the CA performs.

How to get an SSL certificate

Most hosting plans include a free DV certificate issued automatically through Let's Encrypt or a similar authority, valid for 90 days and renewed automatically. On a VPS you can install one with a client such as Certbot. Paid certificates are bought from a CA or a reseller and installed through the control panel or the web server configuration.

Common SSL errors

Certificate expired: renewal failed; renew or fix automatic renewal.
Name mismatch: the certificate does not cover the domain or subdomain being visited.
Mixed content: the page loads over HTTPS but some images or scripts still use http://, so browsers warn or block them.
Incomplete chain: the server does not send the intermediate certificate.
Self-signed certificate: not issued by a trusted authority, so browsers show a warning.

Frequently asked questions

What is the difference between SSL and TLS?

SSL is the older protocol and TLS is its modern replacement. SSL versions are no longer considered secure, so current websites use TLS 1.2 or 1.3, although the term SSL certificate is still used for the same file.

Is a free SSL certificate as secure as a paid one?

For encryption, yes. A free DV certificate from Let's Encrypt uses the same strong cryptography as paid ones. Paid certificates add organization validation, warranties or support, but they do not encrypt any better.

How long does an SSL certificate last?

Certificates have a limited lifetime. Let's Encrypt certificates last 90 days and renew automatically, and public certificates from other authorities are limited to a validity of about a year or less, so renewal must be automated or tracked.

Does SSL help SEO?

HTTPS is a lightweight ranking signal for Google, and browsers label non-HTTPS pages as not secure, which hurts trust and conversions. Using HTTPS is considered a baseline for any site.

How do I fix a "Not Secure" warning?

Install a valid certificate, redirect all HTTP URLs to HTTPS with a 301 redirect, and fix mixed content by updating internal links, images and scripts to HTTPS. Then check the certificate chain with an online SSL test.

Do I need an SSL certificate if I do not take payments?

Yes. Even a simple blog benefits from HTTPS because it prevents tampering, protects logins and contact forms, avoids browser warnings and is expected by search engines.