As IT Pro’s, we know that Extended Validation or EV on web server certificates doesn’t actually add a security layer or harden our web servers in any way but it does give users the warm fuzzy feeling that the website they are using is definitely trustworthy and given that we want our users to believe everything we do internally in IT is trustworthy, it would be great to have our internal web services use Extended Validation certificates for user facing websites.
If you are using a Windows Active Directory Certificates Services (ADCS) certificate authority for issuing your certificates then the great news is that we can do this and it can be made to work in an existing environment so you don’t need to build a new Root CA or setup new servers for it to work, we just need to create a new Certificate Template and a Group Policy Object in the domain.
Configure the Certificate Authority
The first step is to create the Certificate Template. On your ADCS server where you issue your Web Server certificates, open the Certificate Authority MMC console. From the console, right-click on the Certificate Templates folder and select Manage.
Once you have clicked this, another window will open with the list of Certificate Templates configured in the environment. Find the Web Server certificate, right-click it and select the Duplicate Template option.
At the Properties for New Template dialog, enter a display name that is appropriate such as “Web Server with EV” or “Web Server Extended Validation”. From here, click the Extensions tab.
On the Extensions tab, highlight the Issuance Policies list item and select Edit. At the window which appears, select the New button to add a new Issuance Policy.
Give your new issuance policy a name such as “EV Issuance Policy” and if you have one (which you should do for production) enter your Certificate Purpose Statement URI. If you don’t know what a Certificate Purpose Statement (CPS) is then I would suggest the TechNet article Certificate Policies and Certificate Policy Statements as a first primer however in a nutshell, it’s a webpage which gives people information about how the certificates can be used.
Before you hit OK on the New Issuance Policy dialog, note the final field OID. Copy this OID to your clipboard and keep it their for the time being or better yet, save it to a text document in a safe place as we need this for the steps later.
Once you have this, hit OK on the dialog and change any other settings on the template you may need to such as the validity period, the key length or whether you want to allow the private key to be exported. Once you have created the new template, we need to configure the CA to be able to issue it.
As shown above, back in the Certificate Authority console, right-click on the Certificate Templates folder and this time, select New followed by the Certificate Template to Issueoption. From the list of templates, select the new template you just created for Web Server with Extended Validation.
After this, the Certificate Authority is configured with a new template that can be used for Extended Validation and the CA is configured to issue certificates based on that template however it’s no good having the certificates if the clients do not know to trust it to the extent required to display the green address bar.
Configure Group Policy in Active Directory
With the CA configured, we need to configure clients to trust this certificate for Extended Validation and the best method for this is going to be Group Policy. If you have an existing Group Policy to apply certificate related settings then use that policy otherwise create a new one and link it either at the root of your domain to apply it to all computers on the domain or to a particular OU if you only want it to apply to sub-set of clients. Just for clarity, I would not recommend putting certificate related settings in the Default Domain Policy nor would I recommend putting any settings into that policy. The Default Domain Policy and the Default Domain Controllers Policy should be left untouched and new policy objects should be created for any settings you want to apply.
In your Group Policy Object, expand the view in Computer Configuration followed by Security Settings, Public Key Policies and finally Trusted Root Certification Authorities. If you are using an existing policy, you should have here a valid copy of the public key portion of the certificate for your Root CA. If you are creating this as a new policy, you will need to import the public key portion of your Root CA certificate.
Once your certificate is added, right-click it and select the Properties. From the properties, you need to select the Extended Validation tab. On this tab, add the OID that you earlier copied or saved to a text document. Any OIs in this list are considered trusted for Extended Validation when a certificate contains the Issuance Policy matching that OID and the certificate issued by a CA that is part of the issuing or subordinate chain below the specified Root CA.
Once you have applied the GPO to your clients, you can issue a new certificate for a web site with the Web Server Extended Validation template and when browsing to that site from a client computer which both trusts your Root CA and understands the OID applied to the Issuance Policy, you will get the green address bar.