vendredi 19 avril 2013

[DirectAccess] Part 3: Authenticating IP-HTTPS connections with a PKI certificate

In part 1 of this series, we configured DirectAccess for an IP-HTTPS connection in a simple (home) environment. In part 2, we enabled reporting and improved client settings to reduce connection time.

In the two next parts, I propose to improve the security. In this part, we will remove the self-signed certificate used for IP-HTTPS connections and we will generate a certificate from our PKI.
Next part is dedicated to client authentication.

PART 3: AUTHENTICATING IP-HTTPS CONNECTIONS WITH A PKI


1. Preparing PKI

If you don't have a PKI, Install the AD CS (Active Directory Certificate Services) role on a server (your DC if you want).

You can install it from the Server Manager dashboard (add role...) or with powershell with the command lines :
Install-WindowsFeature AD-Certificate -IncludeManagementTools
Install-AdcsCertificationAuthority -Force


For more information, read the instructions on Basic PKI for Windows Server 2012.



2. Remove the self-signed certificate for IP-HTTPS connections

From a server or a computer with a GUI, open a mmc console
Add the snap-in Certificates


Connect on your DirectAccess server


In the Personal Store, find and select the IP-HTTPS certificates
Its friendly name is normally DirectAccess-IPHTTPS


Remove that certificate
Close the mmc console.




3. Request the IP-HTTPS certificate to your PKI

You can't request and import a certificate with a private key if you're not connected locally on the server. So with a core server, don't try to request the IPHTTPS certificates, with a mmc console from another computer.

So, there are 2 solutions:
 - Autoenrollment : you create the IPHTTPS certificates template on your PKI and you define security options to allow only your DirectAccess server to enroll that certificate automatically. Good idea !
 - Request certificate with command lines. Let's do that !


Open a command line option on you DirectAccess Server
In a temporary folder, create (locally or remotely) the file certRequest.inf with the following content:

[NewRequest]
Subject = "CN=<public domain name of your server. For example da.nomizo.fr>"
Exportable = FALSE
KeyLength = 2048
KeyUsage = "CERT_DIGITAL_SIGNATURE_KEY_USAGE | CERT_KEY_ENCIPHERMENT_KEY_USAGE"
MachineKeySet = TRUE
FriendlyName = "IPHTTPS PKI"
[RequestAttributes]
CertificateTemplate="WebServer"


Generate your request file with the command line
certreq -new certRequest.inf certRequest.req


To check the content of your request, use the command line
certutil certRequest.req


Submit your request to your PKI and get you certificate with the command line
certreq -submit certRequest.req IPHTTPS-Cert.cer

Select the CA you want to contact and click on OK


On your CA, you can see the generated certificate


On your DirectAccess server, you can confirm the RequestID


Now that you've got your .cer file, just accept it
certreq –accept IPHTTPS-Cert.cer


With a remote MMC console, you can watch you new IP-HTTPS certificate


For information, this is the IP-HTTPS certificate generated for my DirectAccess Server



Note that I've got an alert for the CA certificate. That's only because my local machine can't confirm that my DirectAccess server trusts the CA certificate.



You can read certreq references on Technet to get more information :
http://technet.microsoft.com/library/cc725793.aspx



4. Define your new IP-HTTPS certificate in DirectAccess

Open the DirectAccess console
In the Step 2 - Remote Access Server Box, click on Edit


On the Network Adapters screen, click on Browse


Select your new IP-HTTPS certificate


You can ensure that you select the right certificate by clicking on Click here to view certificate properties.
Note that private key information is not shown.


Click on OK to select your certificate. The Common Name of your certificate appears.
Click on Next


Click on Finish




5. Update configuration

At the bottom of the screen, click on Finish


Click on Apply


Click on Close


To monitor your server status, click on Dashboard

You will certainly get several alerts and a message that says "Configuration for server servername not yet retrieved from the domain controller"


Just wait or type the command line gpupdate /force to speed the process


If you still receive an alert that says "Configuration for server servername retrieved from the domain controller, but not yet applied.", that means probably that you made a mistake during the IP-HTTPS certificate creation.
See technet for more information about configuration distribution issues.


6. Certificate for NLS Server

With the same method you can replace the self-signed certificate for NLS (Network Location Server) server by a PKI generated certificate.


You can use the certRequest.inf file with the following content

[NewRequest]
Subject = "CN=<NLS name of your server. For example DirectAccess-NLS.sc.lab>"
Exportable = FALSE
KeyLength = 2048
KeyUsage = "CERT_DIGITAL_SIGNATURE_KEY_USAGE | CERT_KEY_ENCIPHERMENT_KEY_USAGE"
MachineKeySet = TRUE
FriendlyName = "NLS PKI"
[RequestAttributes]
CertificateTemplate="WebServer"


Note : Ensure that your DNS record exists. Especially, if you use the same CN than the self-signed certificate, DirectAccess may remove the DNS record.


You can also set an HTTPS server what you can reach on your network. Be careful, that URL must be available ONLY from your internal network, otherwise your clients will suppose it is locating on your network and won't create a DirectAccess communication.




Now, our DirectAccess server use certificates generated from our PKI. It's really more secure !
In the next part, I will show you how to improve client authentication security with certificates.


See you soon
Julien


1 commentaire:

  1. Hi Julien,

    Good stuff, great guide. For some reason when I add the PKI cert for the NLS component when I click the final Finish button it's deleting the DNS record from the records. Other than that all good.

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