What is an SSL certificate
An SSL certificate (Secure Sockets Layer) is a digital document that verifies a website’s authenticity and encrypts the data being transmitted. Today, the TLS (Transport Layer Security) protocol is actually used, but the term “SSL” has stuck for historical reasons.
An SSL certificate changes the website address from http:// to https://, and a lock icon appears in the browser’s address bar.
Why an SSL certificate is needed
An SSL certificate is necessary for several reasons:
- Security — encrypts users’ data (passwords, payment details)
- Trust — the lock icon and HTTPS in the browser help build visitors’ trust
- SEO — Google has used HTTPS as a ranking signal since 2014
- Browsers — Chrome and Firefox mark HTTP sites as “not secure”
- HSTS — modern security standards require HTTPS
Types of SSL certificates
| Type | Verification level | Suitable for |
|---|---|---|
| DV (Domain Validation) | Domain only | Blogs, small websites |
| OV (Organization Validation) | Domain + organization | Corporate websites |
| EV (Extended Validation) | Extended verification | Banks, e-commerce |
| Wildcard | Domain + all subdomains | Websites with subdomains |
How to get an SSL certificate
Free: Let's Encrypt
# Установка certbot
sudo apt install certbot python3-certbot-nginx
# Получение сертификата
sudo certbot --nginx -d example.com -d www.example.comLet's Encrypt is free, valid for 90 days, and renews automatically.
Paid certificate
Paid certificates from DigiCert, Comodo, and GlobalSign have a higher level of verification and extended warranties. OV and EV certificates require organization verification.
Check the installation
curl -I https://example.com
# Ищите: HTTP/2 200 и Strict-Transport-Security заголовокCheck SSL on reChecker
Use SSL Checker to fully analyze your certificate. The tool will show:
- The expiration date and the number of days until it expires
- The certificate type and certificate authority
- The TLS protocol version
- The certificate’s chain of trust
- The encryption algorithm and key length
FAQ
How often should an SSL certificate be renewed? Let's Encrypt certificates renew every 90 days (automatically). Commercial certificates last from 1 to 3 years. Automatic renewal and monitoring are recommended.
Does the type of SSL affect SEO? Google does not distinguish between DV, OV, and EV for rankings — only the presence of HTTPS matters. But EV certificates increase user trust in financial services.
What is mixed content? If a page loads over HTTPS but contains resources (images, scripts) served over HTTP, that is mixed content. The browser blocks these resources and displays a warning.