Intro

In this part we are going to:

Install the subordinate certificate authority
Request and approve a CA certificate from the offline root CA
Configure the subordinate CA for the CRL to work correctly

Required Permissions

You need to be a member of the Enterprise Admins group to complete these tasks.

Procedure

Installing Certificate Services

Just as with the offline Root CA, deploying Certificate Services on Windows Server 2012 R2 is simple, I stuck with PowerShell, view source blog for step-by-step GUI tutorial. Instal-ADCSCertificateAuthority?

Add-WindowsFeature -IncludeManagementTools -Name ADCS-Cert-Authority, `
ADCS-Web-Enrollment, Web-Default-Doc, Web-Dir-Browsing, Web-Http-Errors, `
Web-Static-Content, Web-Http-Redirect, Web-Http-Logging, Web-Log-Libraries, `
Web-Request-Monitor, Web-Http-Tracing, Web-Stat-Compression, Web-Filtering, `
Web-Windows-Auth, Web-ASP, Web-ISAPI-Ext

DNS

In the source guide he talk about creating a CNAME record, since he set his offline Root CA CRL to point to “clr.blah.domain” in my case I specified the direct hostname of the CA. Maybe he did this for obfuscation security reasons, I’m not sure, either way I skipped this since an A host record already exists for the path I entered in the CRL information for the offline root ca.

Configuring Certificate Services

After the Certificate Services roles are installed, start the configuration wizard from Server Manager – click the flag and yellow icon and click the Configure Active Directory Certificate Services… link.

My CA server is core thus no GUI, thus no direct Server Manager. Connect to a client system that has required network access to run Server Manager and point it to the CA server. In this case I’ll be using a Windows 10 client machine. Run Server Manager, and add CA server as Domain/Enterprise Admin account.

Then just like the source blog guide, you should notice a notification at the top right requiring post ADCS configuration deployment.

Use a proper admin account:

Click Next, then select CA and CA Web Enrollment.

Click Next, Configure this subordinate certificate authority as an Enterprise CA. The server is a member of a domain and an Enterprise CA allows more flexibility in certificate management, including supporting certificate auto enrollment with domain authentication.

Click Next, Configure this CA as a subordinate CA. After configuration, we will submit a CA certificate request to the offline root CA.

Click Next, Create a new private key for this CA as this is the first time we’re configuring it. Now I’m curious to see what CertUtil reports after this wizard and what the RSA directories on the CA will contain. They should contain the keys, right?!

Click Next, leave the defaults, again simply going to use RSA @ 2048 Key Length, with a SHA256 hash checksum. Should remain the standard for hopefully the next 10 years.

Click Next,

Click Next, because this is a subordinate CA, we’ll need to send a CA certificate request to the offline root CA. Save the request locally which will be used later to manually request and approve the certificate. This is saved to the root of C: by default. Again oddly the initial Common name is auto generated into the request name with no option to alter it…

Moving along, click next, and specify the DB location. Generally leave the defaults.

Finally Summary and confirmation.

Click Configure and the wizard will configure the certificate services roles. Note the warning that the configuration for this CA is not complete, as we still need to request, approve and import the CA certificate.

Configuring the CRL Distribution Point

Before configuring the Certification Authority itself, we’ll first copy across the certificate and CRL from the root CA.

Ensure the root CA virtual machine is running and copy the contents of C:\Windows\System32\certsrv\CertEnroll from the root CA to the same folder on the subordinate CA. This is the default location to which certificates and CRLs are published. Keeping the default locations will require the minimum amount of configuration for the CRL and AIA distribution points.

The result on the subordinate certificate authority will look something like this – note that the CRL for the root CA is located here:

In my case it’s an offline (non domain joined) making a shareable UNC path is slightly painful in these cases, and for the most part, it is completely offline, and no NIC settings are even defined on the VM, heck I could remove the vNic completely :D. Anyway to complete this task I did the usual vUSB (a VMDK I mount to different VMs as needed to transfer files) and copied the resulting files specified above into this VMDK, then attached to the Sub CA VM, and moved files to their appropriate path. Again in this case the Sub CA is Core, so either use diskpart, or Server Manager from the client machine to bring the disk online and mount it.

Issuing the Subordinate CA Certificate

Next, we will request, approve the certificate request for the subordinate CA. At this point, the subordinate CA is un-configured because it does not yet have a valid CA certificate.

Copy the initial request created by the confiz wizard to the movable VMDK.

Now, remove the disk from the Sub CA and attach it to the Off-line root CA, then open up the CA tool to request a new certificate. (Don’t worry about taking the disk offline, it’ll unmount automagically).

Browse to where the certificate request for the subordinate certificate authority is located and open the file.

The certificate request will then be listed under Pending Requests on the root CA. Right-click the request, choose All Tasks and Issue.

The subordinate CA’s certificate will now be issued and we can copy it to that CA. View the certificate under Issued Certificates. Right-click the certificate, click Open and choose Copy to File… from the Details tab on the certificate properties.

Export the new certificate to a file in PKCS format. Copy the file back to the subordinate certificate authority, so that it can be imported and enable certificate services on that machine.

Configuring the Subordinate CA

With the certificate file stored locally to the subordinate CA, open the Certificate Authority console – note that the certificate service is stopped. Right-click the CA, select All Tasks and choose Install CA Certificate…

So from a client system open the CA snap-in, point to the new sub CA…

This is where I got stuck for a good while, all the guides I found online were using CA’s with Desktop experience enabled allowing them to run the CA MMC Snap-in locally, and from all my testing against a Server 2016 Core server running the CA role, the snap-in simply wouldn’t load the input wizard…

So I posted the bug on Technet, and Mark saved my bacon!

“You will need to use the commandline to do this. On the CA itself:

1) Open a command prompt

2) Navigate to where your certificate file is located

3) certutil -installcert <your certificate file name here>”

WOOOOOO! We have a working Enterprise Sub-CA… Now the question on if CRL works, and how to deploy the chain properly to servers and clients so things come up with a trusted chain and a green check mark!

“If the CRL is online correctly, the service should start without issues.

To be Continued…..

Intro

Continuing on from my source blog post. In this case he goes on to install and configure the role to be a subordinate enterprise CA. But what do you do if you already deployed an Enterprise Root CA? I’m going to go off a hunch and that something gets applied into AD somewhere to present this information to domain clients. I found this nice article from MS directly on the directions to take, it stated for Server 2012, so I hope the procedure on this hasn’t changed much in 2016.

*NOTE* All steps that state need to be done to AD objects, those commands are run as a Domain Admin, or Enterprise Admin directly logged onto those servers. Most other commands or steps will be done via a client system MMC Snap-in, or logged directly into the CA server.

Remove Existing Enterprise Root CA

Revoke Existing Certificates

Step 1: Revoke all active certificates that are issued by the enterprise CA

1. Click Start, point to
   Administrative Tools, and then click Certification Authority.
2. Expand your CA, and then click the Issued Certificates folder.
3. In the right pane, click one of the issued certificates, and then press CTRL+A to select all issued certificates.
4. Right-click the selected certificates, click All Tasks, and then click Revoke Certificate.
5. In the Certificate Revocation dialog box, click to select Cease of Operation as the reason for revocation, and then click OK.

Simple enough…

 

Increase the CRL interval

Step 2: Increase the CRL publication interval

1. In the Certification Authority Microsoft Management Console (MMC) snap-in, right-click the Revoked Certificates folder, and then click Properties.
2. In the CRL Publication Interval box, type a suitably long value, and then click OK.

Note The lifetime of the Certificate Revocation List (CRL) should be longer than the lifetime that remains for certificates that have been revoked.

Easy enough, done and done.

Step 3: Publish a new CRL

1. In the Certification Authority MMC snap-in, right-click the
   Revoked Certificates folder.
2. Click All Tasks, and then click
   Publish.
3. In the Publish CRL dialog box, click
   New CRL, and then click OK.

Again easy, done.

Deny Pending Requests

*DEFAULT, generally Not required.

Step 4: Deny any pending requests

By default, an enterprise CA does not store certificate requests. However, an administrator can change this default behavior. To deny any pending certificate requests, follow these steps:

1. In the Certification Authority MMC snap-in, click the Pending Requests folder.
2. In the right pane, click one of the pending requests, and then press CTRL+A to select all pending certificates.
3. Right-click the selected requests, click All Tasks, and then click Deny Request.

Not the case for me.

Uninstall Certificate Services

Step 5: Uninstall Certificate Services from the server

1. To stop Certificate Services, click Start, click Run, type cmd, and then click OK.
2. At the command prompt, type certutil -shutdown, and then press Enter.
3. At the command prompt, type
   certutil -key, and then press Enter. This command will display the names of all the installed cryptographic service providers (CSP) and the key stores that are associated with each provider. Listed among the listed key stores will be the name of your CA. The name will be listed several times, as shown in the following example:

(1)Microsoft Base Cryptographic Provider v1.0:
1a3b2f44-2540-408b-8867-51bd6b6ed413
MS IIS DCOM ClientSYSTEMS-1-5-18
MS IIS DCOM Server
Windows2000 Enterprise Root CA
MS IIS DCOM ClientAdministratorS-1-5-21-436374069-839522115-1060284298-500

4. Delete the private key that is associated with the CA. To do this, at a command prompt, type the following command, and then press Enter:

certutil -delkey CertificateAuthorityName

Note If your CA name contains spaces, enclose the name in quotation marks.

In this example, the certificate authority name is “Windows2000 Enterprise Root CA.” Therefore, the command line in this example is as follows:

certutil -delkey “Windows2000 Enterprise Root CA”

* OK, this is where things got weird for me. For some reason I wasn’t getting back the same type of results as the guide, instead I got this:

C:\ProgramData\Microsoft\Crypto\RSA>certutil –key
Microsoft Strong Cryptographic Provider:
TSSecKeySet1
f686aace6942fb7f4566yh1212eef4a4_ae5889t-54c3-4b6f-8b60-f9f8471c0525
RSA
AT_KEYEXCHANGE

CertUtil: -key command completed successfully.

And any attempt to delete the key based on the known CA name just failed. I asked about this in TechNet under the security section, and was told basically what I figured and that the key either didn’t exist or was corrupted. So basically continue on with the steps. It was later answered by Mark Cooper.

Locating the CA Master Key

This one again got answered by Mark Cooper, include –csp ksp (keys are located under: %allusersprofile%\Microsoft\Crypto\Keys)

Deleting the CA Master Key

From all the research I’ve done, it seems people are adamant that you delete the key before you remove the certs, why exactly I’m not sure…(From my testing if you deleted the certificate via certutil, it comes right back when restarting certsvc. It must be rebuilt from the registry?)

So: certutil –csp ksp –delkey <key>

Checking the keys directory show empty. Good stuff.

Viewing the Certificate store

Certutil –store my

This made me start to wonder where the actual certificate files were stored, a google away and it turns out to be in the registry? Lol (HKLM\System\Microsoft\SystemCertificates)

Nothing more than just a string of obfuscated code (much like opening up a CSR), so the only way to interact with them is using the Microsoft CryptoAPI (CertUtil), or the Snap-in.

Deleting the CA Certificate

Certutil –delstore my <Serial>

Reopening regedit, and the cert is gone.

Delete Trusted Root CA Cert

Certutil –store ca
Certutil –delstore ca <serial>

So moving on…*

5. List the key stores again to verify that the private key for your CA was deleted.
   Check
6. After you delete the private key for your CA, uninstall Certificate Services. To do this, follow these steps, depending on the version of Windows Server that you are running.
   

   Uninstall-AdcsCertificationAuthority

   If the remaining role services, such as the Online Responder service, were configured to use data from the uninstalled CA, you must reconfigure these services to support a different CA. After a CA is uninstalled, the following information is left on the server:

7. • The CA database (To be deleted see below)
   • The CA public and private keys (Deleted see above)
   • The CA’s certificates in the Personal store (Deleted See above)
   • The CA’s certificates in the shared folder, if a shared folder was specified during AD CS setup (N/A)
   • The CA chain’s root certificate in the Trusted Root Certification Authorities store (Deleted See Above)
   • The CA chain’s intermediate certificates in the Intermediate Certification Authorities store (none existed for me)
   • The CA’s CRL (yup)

By default, this information is kept on the server in case you are uninstalling and then reinstalling the CA. For example, you might uninstall and reinstall the CA if you want to change a stand-alone CA to an enterprise CA.

Known AD CA Objects

Step 6: Remove CA objects from Active Directory

When Microsoft Certificate Services is installed on a server that is a member of a domain, several objects are created in the configuration container in Active Directory.

These objects are as follows:

• certificateAuthority object
  • Located in CN=AIA,CN=Public Key Services,CN=Services,CN=Configuration,DC=ForestRootDomain.
  • Contains the CA certificate for the CA.
  • Published Authority Information Access (AIA) location.
• crlDistributionPoint object
  • Located in CN=ServerName,CN=CDP,CN=Public Key Service,CN=Services,CN=Configuration,DC=ForestRoot,DC=com.
  • Contains the CRL periodically published by the CA.
  • Published CRL Distribution Point (CDP) location
• certificationAuthority object
  • Located in CN=Certification Authorities,CN=Public Key Services,CN=Services,CN=Configuration,DC=ForestRoot,DC=com.
  • Contains the CA certificate for the CA.
• pKIEnrollmentService object
  • Located in CN=Enrollment Services,CN=Public Key Services,CN=Services,CN=Configuration,DC=ForestRoot,DC=com.
  • Created by the enterprise CA.
  • Contains information about the types of certificates the CA has been configured to issue. Permissions on this object can control which security principals can enroll against this CA.

When the CA is uninstalled, only the pKIEnrollmentService object is removed. This prevents clients from trying to enroll against the decommissioned CA. The other objects are retained because certificates that are issued by the CA are probably still outstanding. These certificates must be revoked by following the procedure in the “Step 1: Revoke all active certificates that are issued by the enterprise CA” section.

For Public Key Infrastructure (PKI) client computers to successfully process these outstanding certificates, the computers must locate the Authority Information Access (AIA) and CRL distribution point paths in Active Directory. It is a good idea to revoke all outstanding certificates, extend the lifetime of the CRL, and publish the CRL in Active Directory. If the outstanding certificates are processed by the various PKI clients, validation will fail, and those certificates will not be used.

If it is not a priority to maintain the CRL distribution point and AIA in Active Directory, you can remove these objects. Do not remove these objects if you expect to process one or more of the formerly active digital certificates.

Remove all Certification Services objects from Active Directory

To remove all Certification Services objects from Active Directory, follow these steps:

1. Know the CA common name (use CertUtil)
2. Use Sites and Service MMC Snap-in from a client computer using a domain admin account with proper permissions, highlight the parent snap-in node -> View (from the toolbar) -> Show Services Node.
3. Expand Services, expand Public Key Services, and then click the AIA folder.
4. In the right pane, right-click the CertificationAuthority object for your CA, click Delete, and then click “Yes”.
5. Left Nav, Click CDP folder.
6. In the right pane, right-click the CertificationAuthority object for your CA, click Delete, and then click “Yes”.
7. Left Nav, Click Certificate Authority.
8. In the right pane, right-click the CertificationAuthority object for your CA, click Delete, and then click Yes.
9. Left Nav, Click Enrollment Services (This should have been auto removed, in my case it was)
10. If you did not locate all the objects, some objects may be left in the Active Directory after you perform these steps. To clean up after a CA that may have left objects in Active Directory, follow these steps to determine whether any AD objects remain:
    1. Type the following command at a command line, and then press ENTER:
       1. ldifde -r “cn=CACommonName” -d “CN=Public Key Services,CN=Services,CN=Configuration,DC=ForestRoot,DC=com” -f output.ldf
    2. In this command, CACommonName represents the Name value that you determined in step 1. For example, if the Name value is “CA1 Contoso,” type the following:
       1. ldifde -r “cn=CA1 Contoso” -d “cn=public key services,cn=services,cn=configuration,dc=contoso,dc=com” -f remainingCAobjects.ldf
    3. Open the remainingCAobjects.ldf file in Notepad. Replace the term “changetype: add” with “changetype: delete.” Then, verify whether the Active Directory objects that you will delete are legitimate.
    4. At a command prompt, type the following command, and then press ENTER to delete the remaining CA objects from Active Directory:
       1. ldifde -i -f remainingCAobjects.ldf

At this point I was having issues with the input command of the ldf file was failing. I posted these results in my Technet post. After a bit more research I noticed other examples online not having any other information appended after the “changetype: delete” line. So I simply followed along and did the same deleting all the lines after that one, leaving the base DN object in place and sure enough it finally succeeded.

Generate base object LDF file:

After editing line as specified in MS article:

New altered LDF file:

Same command after altering file:

Second run I simply deleted the object under the KRA folder, and it returns no values.

13) Delete the certificate templates if you are sure that all of the certificate authorities have been deleted. Repeat step 12 to determine whether any AD objects remain.

I did this via the Site and Service Snap-in, under the PKI section of the Services node.

Delete NTAuthCertificates Objects Published Certificates

Step 7: Delete certificates published to the NtAuthCertificates object

After you delete the CA objects, you have to delete the CA certificates that are published to the NtAuthCertificates object. Use either of the following commands to delete certificates from within the NTAuthCertificates store:

certutil -viewdelstore “ldap:///CN=NtAuthCertificates,CN=Public Key
Services,…,DC=ForestRoot,DC=com?cACertificate?base?objectclass=certificationAuthority”

certutil -viewdelstore “ldap:///CN=NtAuthCertificates,CN=Public Key
Services,…,DC=ForestRoot,DC=com?cACertificate?base?objectclass=pKIEnrollmentService”

Note You must have Enterprise Administrator permissions to perform this task.

The -viewdelstore action invokes the certificate selection UI on the set of certificates in the specified attibute. You can view the certificate details. You can cancel out of the selection dialog to make no changes. If you select a certificate, that certificate is deleted when the UI closes and the command is fully executed

Use the following command to see the full LDAP path to the NtAuthCertificates object in your Active Directory:

certutil store -? | findstr “CN=NTAuth”

Nice and easy, finally.

Delete the CA Database

Step 8: Delete the CA database

When Certification Services is uninstalled, the CA database is left intact so that the CA can be re-created on another server.

To remove the CA database, delete the %systemroot%\System32\Certlog folder.

Nice and easy, I like these steps.

Clean up the DC’s

Step 9: Clean up domain controllers

After the CA is uninstalled, the certificates that were issued to domain controllers must be removed.

Which states for 2003 and up:

certutil -dcinfo deleteBad

My results:

With the same list of garbage for the DC, then rerunning Certutil –dcinfo, still reported the same certs… So I had to manually remove these, but again opening a MMC snap-in via a client system, add the certificate snap-in and point to the machine store on the DC’s. Then manually delete the certificates, once this was done for both DC’s. CertUtil –dcinfo finally reported clean…

Summary

Finally!!! What a gong show it is to remove an existing CA from an environment… even one that literally wasn’t used for anything outside its initial deployment as an enterprise root CA.