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Beginning with Windows Server 2003, Microsoft has enhanced its own PKI-solution with several new features like:
- Key Archiving and Recovery
- Role Separation
- Qualified subordination
- Version 2 Certificate Templates
To get these entire wonderful new features, you must buy Windows Server 2003 Enterprise, because the Standard Version of Windows Server 2003 doesn't offer these features.
One of the biggest enhancements is the Key Archiving and Reovery feature. With this feature, every certificate (the private key) issued by a Windows 2003 Enterprise CA will be archived at the CA. Key Archiving is not available for certificates with an e-mail signature only purpose.
In this article we will issue an e-mail certificate for the user MSEXCHANGEORG and assume that this user has lost his e-mail certificate. With the help of a Key Recovery Agent (KRA) and the Windows Server 2003 Resource Kit Utility KRT.EXE we will recover this certificate.
This article will give you only a high level overview about the entire process. If you have more questions, follow the links at the end of this article.
Key Archiving and Recovery requires multiples steps:
- Enabling the Key Recovery Agent
- Enable the CA for key archiving
- Issue e-mail certificates to users
- Recover e-mail certificates (KRT and CERTUTIL)
Enabling the Key Recovery Agent
First, we need to enable a Key Recovery Agent. A Key Recovery Agent is a highly trusted person which is responsible for recovering lost or damaged archived certificates for users.
We must issue a Key Recovery Agent certificate for this user. To do this:
- Start the Windows 2003 CA console
- Issue a new template named Key Recovery Agent
- Request this certificate for the user who becomes the Key Recovery Agent
- Manually Issue the Key Recovery Agent Certificate at the CA
Figure 1 shows the issued Key Recovery Agent Certificate for the user Administrator.
Figure 1: Issued Key Recovery Agent certificate
The Windows 2003 CA will not automatically issue this certificate to the user who requests the Key Recovery Agent certificate. The CA Administrator must manually Issue the certificate in the Microsoft CA MMC under Pending Requests.
Enable the CA for key archiving
Now it is time to enable the CA for Key Archiving. Start the Microsoft CA MMC and navigate to the CA properties – Recovery Agents.
Because Key Reovery is a very security sensible process, you can specify how many Recovery Agents are required to Archive keys. Click Add to import the Key Recovery Agent certificate. Click OK and restart the CA service.
Figure 2: Enable the CA for Key archiving
Now it is time to duplicate an e-mail Certificate Template at the Windows 2003 CA. The question is why? The default e-mail Certificate Template doesn't allow the archiving of the subject's private key. Start the Microsoft CA MMC, navigate to Certificate Templates and rightclick Manage – Select the Exchange User Certificate Template and click Duplicate and name the new template. In the Request Handling section click Archive subject's encryption private key.
Figure 3: Enable Key Archiving in the Certificate Template
The new Certificate Template (Exchange User (KeyARC) is now ready to issue certificates and to archive keys.
Figure 4: New certificate template
Issue e-mail certificates to users
It is possible to auto enroll user- and machine certificates for all users and computers with Active Directory and Group Policies. Auto enrollment for Users and machines requires a Windows 2003 Active Directory environment and Windows XP clients. For more information about Certificate Auto enrollement, click the link at the end of this article. For this article the user MSEXCHANGEORG will request an Exchange User (KeyARC) certificate manually.
Figure 5: Request an Exchange user (KeyARC) certificate
Recover e-mail certificates (KRT and CERTUTIL)
In this article we will now assume that the user MSEXCHANGEORG has lost its e-mail certificate and he can't encrypt new e-mails and he can't decrypt existing E-Mails. Without central Key Archiving at the Windows 2003 CA you are now in trouble.
Let us see how easy it is to recover a lost certificate with the Private Key.
There are two ways to recover the certificate:
CERTUTIL is the built-in Command Line tool to administer a Windows 2003 CA from the command line. CERTUTIL has several switches for CA administration and Key Recovery.
The Key Recovery Tool (KRT.EXE) is a new tool which is part of the Windows Server 2003 Resource Kit Utilities. KRT is a GUI extension for the builtin Windows 2003 CA tool CERTUTIL. In this article, we will use the Key Recovery Tool (KRT).
To recover a certificate we need a unique value for the certificate to recover. We will use the certificate Serial Number. You can find the certificate Serial Number in the Issued Certificate section of the Microsoft CA MMC. As you can see in Figure 6 there is an archived Key for the user MSEXCHANGEORG (to see if the certificate key was archived, add the Archived Key section).
Figure 6: Determine the Certificates Serial Number
After downloading and installing the Windows 2003 Reource Kit utilities, start the Key Recovery Tool. Select the issuing Certification authority (CA). As Search Criteria select Certificate Serial Number and enter the Serial Number for the certificate to recover. Now click Search, select the Certificate and click Recover.
Figure 7: Recovery the users Private Key
You can save the recovered certificate in a file that contains the certificate Serial Number with a PFX extension. I recommend changing the name of the PFX file so it is easier for a user to know what he or she is doubleclicking.
Figure 8: Save the recovered certificate
Now it is time to transmit the certificate to the user. Don't use an E-Mail for delivery because the PFX file contains the private Key for this user. At the user's site, the user can import this certificate by a simple doubleclick.
Key Archiving is a powerful weapon for the Administrator to reduce the time to recover a user's private certificate. On the other hand, it is important to secure the CA (Physical and logical) and to give this feature for Key Recovery only to highly trusted Administrators.
Certificate Autoenrollment in Windows Server 2003
Managing a Windows Server 2003 Public Key Infrastructure
Exchange 2000 Key Management Server Migration to a Windows 2003 CA
Windows 2003 Resource Kit Tools