* Option 1: use DirectAdmin Web Control.
1. First logon as user 'admin' 
2. Modify the 'Access Level' from 'Admin Level' to 'User Level', by clicking in the Access Level menu on the right on User Level . 
Click underneath Advanced Features on SSL Certificates.
3. Select the option 'Create a Certificate Request' and enter all requested information, when you are done click Save.
4. Select and copy the Information you see in the text box (just the Certificate Request part).
It is important that you make a backup of the Request part and the Private Key! 
Paste the CSR in the enrollment form at the networking4all website and order your certificate.
copy all and paste into this tool can test CSR is valid and accurate or not: https://cryptoreport.websecurity.symantec.com/checker/views/csrCheck.jsp
Copy the entries of CSR file and send it to VietNamHost , or paste it to the online SSL order screen on VietNamHost website.
After you receive your SSL Certificate from VietNamHost, you can install it.
* Method 2: using OpenSSL on Linux CentOS.
