You can add two different types of certificates in your DreamHost panel:
- Free 'Let's Encrypt' certificate
- Paid Comodo certificate
The differences between these are described below.
Free Let's Encrypt SSL certificates
Let's Encrypt is a Certificate Authority (CA) that offers FREE SSL certificates that are just as secure as current paid certificates, although a paid certificate is still recommended for e-commerce sites since 'Let's Encrypt' certificates do not offer 'Organizational Validation'. This project was pioneered to make encrypted connections the default standard throughout the Internet.
View the following articles for further information:
Paid Professionally-signed certificate ($15/year)
As mentioned above, a self-signed certificate throws a browser warning when visiting the site. If you have a customer facing site, or more importantly, a site that handles sensitive information such as passwords and credit card data, a paid Comodo certificate is highly recommended.
Paid certificates show no browser warnings and offer additional information in the certificate to ensure its authenticity. For example, these certificates include Organizational Validation (OV) which gives your users more peace of mind to ensure the certificate was correctly issues to a legitimate organization.
If you’d like to purchase a professionally-signed certificate, view the following article
A Unique IP address is NOT required to use an SSL certificate. However, if you plan to use an eCommerce application it's strongly recommend that you add a Unique IP address to provide maximum compatibility with older Internet browsers.
For more information about Unique IP addresses (including instructions for adding one to your domain), take a look at the Unique IP article.