Domain Validated (DV) SSL certificates are the most basic of the three types of SSL/TLS certificates. While Organization Validated (OV) and Extended Validated (EV) require multiple steps in which the Certificate Authority vets the company or organization applying for the certificate, Domain Validation is just a single step. The Certificate Authority must simply verify that the person or organization applying for the certificate owns the registered domain.
What is Domain Validation?
To satisfy the Domain Validation requirement you must prove you own the domain that was submitted with the order.
The easiest, and most preferred method for accomplishing this is via email-based authentication. During email-based authentication, the CA will send an email to the WHOIS registrar email address asking them to verify that they did indeed register for a certificate. Once you respond to that email in the affirmative, the requirement is considered satisfied and the certificate is issued.
If you cannot satisfy the Domain Validation requirement via email, there are alternative methods as well.
There are two additional ways to satisfy the Domain Validation requirement, though one of them is exclusive to Comodo.
Those alternative methods are:
The CA will provide you with a text file that you will need to upload to the root directory of your website. This will then be verified by the CA via HTTP or HTTPS.
CNAME-Based Authentication (Comodo Only)
Comodo will provide you with two unique hash values (these are MD5 and SHA1). You, in turn, must enter them in your CNAME DNS record. You must use the following format: <MD5 hash>.yourdomain.com CNAME <SHA-1 hash>.comodoca.com. Once this is complete, Comodo will check on it and use it to satisfy the Domain Validation requirement.