What is SSL?

SSL

SSL (Secure Sockets Layer) is the original name of the technology that encrypts the connection between a browser and a website. The SSL protocol itself has been replaced by the more secure TLS (Transport Layer Security), but people still say “SSL certificate” for the certificate that makes HTTPS work.

What an SSL certificate does

Encrypts data such as passwords, form entries and card details, so others on the network can’t read it.
Proves identity: a trusted certificate authority confirms that the certificate belongs to the domain.
Enables HTTPS: browsers show the site as secure instead of warning “Not secure”.

Types of certificates

Domain validated (DV): proves control of the domain. Free from Let’s Encrypt and included with most hosting.
Organization validated (OV) and extended validation (EV): also check the company behind the site.
Wildcard and multi-domain: cover all subdomains, or several domains, with one certificate.

SSL and SEO

HTTPS is a lightweight Google ranking signal, and browsers warn visitors about sites without it. Certificates expire, so let them renew automatically: the maximum lifetime of public certificates is being cut step by step, starting with 200 days from March 2026.

SSL certificate example

A visitor opens a shop’s checkout page and the browser shows a padlock. Behind it, the shop has a TLS certificate from a trusted authority, issued for its domain. When the certificate expires and the shop forgets to renew it, visitors see a full-page warning that the site is not safe, and sales stop until it is renewed.

SSL certificate checklist

Use a certificate that covers your domain and subdomains, such as a wildcard or a multi-name certificate.
Turn on automatic renewal and set an alert a few weeks before expiry.
Redirect HTTP to HTTPS and fix mixed content.
Use a modern TLS version and test the configuration with a free online tester.
Check the certificate chain, so that all browsers trust it.

SSL certificate mistakes

Letting the certificate expire.
Installing the certificate for www but not the bare domain, or the reverse.
Paying for an expensive certificate when a free domain-validated one is enough for a normal site.
Leaving old HTTP links and images on pages.

SSL FAQs

Is SSL the same as HTTPS?

The certificate enables HTTPS. SSL is the old name of TLS. See HTTP.

Which certificate type do I need?

Most sites need only domain validation. Banks and large shops sometimes use organisation validation. See DNS and CDNs.

SSL