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Building a Certificate Authority in Windows Server 2019 Part 2 – Subordinate CA Setup

2.1 Subordinate Certificate Authority Server Setup

Provision and configure a new Virtual Machine called TFS-CA01 and install Windows Server 2019 Standard (Desktop Experience) using the following settings:

  • Virtual CPU – 2
  • Virtual Memory – 8192 MB
  • Virtual Hard Disk – 60 GB
  • Virtual Floppy Drive – 1
  • Virtual Network Adapters – 1

Join the TFS-CA01 Virtual Machine to the TFS Labs Domain. Once it has been completely setup you can proceed to the next steps on configuring the Active Directory Certificate Services role.

2.2 Create CNAME Records in DNS

By splitting the Active Directory Certificate Authority services into separate CNAME records, it would make it possible to split up the role in the future if needed. On the TFS-DC01 Domain Controller, create the following CNAME records pointing the TFS-CA01 Server:

  1. Open the DNS Manager Console (dnsmgmt.msc).
  2. Under the DNS Node, expand the TFS-DC01 Server and then expand Forward Lookup Zones. Select and the corp.tfslabs.com Zone. Right-click New Alias (CNAME) (repeat for steps 3 to 4).
  3. In Alias name (uses parent domain if left blank), enter OCSP as the name. In the Fully qualified domain name (FQDN) field, enter tfs-ca01.corp.tfslabs.com. and then click OK.
  4. In Alias name (uses parent domain if left blank), enter PKI as the name. In the Fully qualified domain name (FQDN) field, enter tfs-ca01.corp.tfslabs.com. and then click OK.
  5. Close the DNS Manager Console.

2.3 Enterprise CA CAPolicy.inf Installation

On the TFS-CA01 Server, create a file in the C:\Windows folder called CAPolicy.inf (ensure that it is saved with the inf extension and not with the txt extension, otherwise these settings will be ignored). Copy the following contents into this file:

[Version]
Signature=”$Windows NT$”

[PolicyStatementExtension]
Policies=AllIssuancePolicy,InternalPolicy
Critical=FALSE

; AllIssuancePolicy is set to the OID of 2.5.29.32.0 to ensure all Certificate templates are available.
[AllIssuancePolicy]
OID=2.5.29.32.0

[InternalPolicy]
OID=1.2.3.4.1455.67.89.5
Notice="The TFS Labs Certification Authority is an internal resource. Certificates that are issued by this Certificate Authority are for internal usage only."
URL=http://pki.corp.tfslabs.com/cps.html

[Certsrv_Server]
; Renewal information for the Enterprise CA.
RenewalKeyLength=4096
RenewalValidityPeriod=Years
RenewalValidityPeriodUnits=5

; Disable support for issuing Certificates with the RSASSA-PSS algorithm.
AlternateSignatureAlgorithm=0

; Load all of the templates by default.
LoadDefaultTemplates=1

Note: You can update the OID number in the InternalPolicy section for your deployment if it is required. The OID number in this example is used in Microsoft examples, but it should work for your organization if it is only ever going to be used internally. You can register for one if you would like to through IANA.

Signature Algorithm Support Issues

The AlternateSignatureAlgorithm=0 flag in the CAPolicy.inf file explicitly uses SHA256 for the algorithm instead of RSASSA-PSS. This can cause issues with some devices (especially iOS) and by ensuring that it is disabled you shouldn’t have issues with these certificates.

2.4 Active Directory Certificate Services Role Installation

The Active Directory Certificate Services Role needs to be installed on the TFS-CA01 Server now that the CAPolicy.inf file is in place and ready to be used.

  1. Open the Server Manager Console (servermanager.exe), click on the Manage menu, and click on Add Roles and Features to start the installation wizard.
  2. On the Before You Begin screen, click the Next button to continue.
  3. On the Installation Type screen, select the option for Role-based or feature-based installation and click the Next button to continue.
  4. On the Server Selection screen, verify that the TFS-CA01.corp.tfslabs.com Server is selected and click Next.
  5. On the Server Roles screen, select the Active Directory Certificate Services option.
  6. The installation wizard will ask to install the necessary management tools for the role. Click the Add Features button to continue.
  7. On the Server Roles screen, click the Next button to continue.
  8. On the Features screen, click the Next button to continue.
  9. On the Active Directory Certificate Services screen, click the Next button to continue.
  10. On the Role Services screen, select the option for Certification Authority and Certificate Authority Web Enrollment. The installation wizard will ask to install the necessary Role and Features for IIS. Click the Add Features button to continue. Once that has been completed, click the Next button to continue.
  11. On the Web Server Role (IIS) screen, click the Next button to continue.
  12. On the Select Role Services screen, click the Next button to continue.
  13. On the Confirmation screen, select the option to Restart the destination server automatically if required. When prompted with a warning about restarting the Server, click the Yes button (the Server must restart in order to continue). Click the Install button to continue.
  14. Once the installation is completed, click the Close button.

2.5 Active Directory Certificate Services Role Configuration

Once the Active Directory Certificate Services role has been added, it will need to be properly configured. In the process of configuring the role for the TFS Labs Domain, the following will be configured:

Cryptographic ProviderRSA#Microsoft Software Key Storage Provider
Key Length4096 Bits
Signature AlgorithmSHA256RSA
Signature Hash SignatureSHA256
CA Common NameTFS Labs Enterprise CA
Validity Period5 Years (Configured from Root CA)
  1. To begin the configuration of Active Directory Certificate Services, open the Server Manager Console (servermanager.exe). Click the Notifications icon in the upper-right hand corner and click the Configure Active Directory Certificate Services on the destination server link in the Post-deployment Configuration box.
  2. On the Credentials screen, verify that the Administrator credentials is set to a Domain Administrator Account and click the Next button to continue. If you do not use a Domain Administrator account, then the installation will not allow you to install the Active Directory Certificate Services service correctly.
  3. On the Role Services screen, select the options for Certification Authority and Certification Authority Web Enrollment and click Next to continue.
  4. On the Setup Type screen, select the option for Enterprise CA and click the Next button to continue.
  5. On the CA Type screen, ensure that the Subordinate CA option is selected and click the Next button to continue.
  6. On the Private Key screen, verify that the Create a new private key option is selected. This is because this a new CA installation and the Private Key is not being restored from a previous Server. Click the Next button to continue.
  7. On the Cryptography for CA screen, make the following changes and then click the Next button to continue:
    • Cryptographic Provider: RSA#Microsoft Software Key Storage Provider
    • Key Length: 4096
    • Hash Algorithm: SHA256
  8. On the CA Name screen, set the Common Name (CN) for the CA to TFS Labs Enterprise CA and click the Next button to continue.
  9. On the Certificate Request screen, accept the default location for saving the Certificate Request file. It will be saved as C:\TFS-CA01.corp.tfslabs.com_corp-TFS-CA01-CA.req. Click the Next button to continue.
  10. On the CA Database screen, make no changes to the database location and click the Next button to continue.
  11. On the Confirmation screen, verify that the options are correct and click the Configure button to commit the changes.
  12. On the Results screen, click the Close button.

Once the Request file has been successfully generated, it will need to be copied to the RootCAFiles Virtual Floppy Disk since the Root CA on TFS-ROOT-CA needs the request file in order to issue the Subordinate Certificate:

  1. Add the RootCAFiles Virtual Floppy Disk to the TFS-CA01 Virtual Machine.
  2. Browse to the C:\ Drive and copy the TFS-CA01.corp.tfslabs.com_corp-TFS-CA01-CA.req to the A:\ Drive.
  3. Leave the RootCAFiles Virtual Floppy Disk inserted.

2.6 Install the Root Certificate

On the TFS-CA01 Server, the TFS Labs Root Certificate needs to be installed to complete the Certificate Chain after the Subordinate Certificate has been issued:

  1. Open the A:\ Drive folder.
  2. Right-click on the TFS Labs Certificate Authority.cer file and select the Install Certificate option.
  3. On the Certificate Import Wizard screen, select the Local Machine for the Store Location and click the Next button.
  4. When prompted for the Certificate Store location, click the Browse button and select the Trusted Root Certification Authorities store and click the OK button. Click the Next button to continue.
  5. Click the Finish button to complete the wizard.
  6. Click the OK button to close the wizard.

2.7 Create the CertData Virtual Directory

On the TFS-CA01 Server, create a folder that will be used to host important Certificate Files for the Domain Users, Workstations and Servers:

  1. On the Root of the C:\ Drive, create a folder called CertData (C:\CertData).
  2. Open the A:\ Drive and copy the TFS Labs Certificate Authority.crl and TFS-ROOT-CA_TFS Labs Certificate Authority.crt files to the C:\CertData folder.
  3. Eject the RootCAFiles Virtual Floppy Disk.
  4. Open the Internet Information Services (IIS) Manager Console.
  5. On the Connections pane, expand TFS-CA01 and then expand Sites.
  6. Right-click on Default Web Site and select Add Virtual Directory.
  7. On Add Virtual Directory page, in Alias, enter CertData. For the Physical path, enter C:\CertData and then click OK.
  8. In the Connections pane, under the Default Web Site, ensure the CertData virtual directory is selected.
  9. In the CertData Home pane, double-click on Directory Browsing.
  10. In Actions pane click Enable.
  11. Close the Internet Information Services (IIS) Manager Console.

2.8 Enable Double Escaping

On the TFS-CA01 Server, enable Double Escaping in IIS in order to allow for proper CRL publication on the TFS Labs Domain.

  1. Open an Administrative Command Prompt.
  2. Type cd C:\Windows\System32\inetsrv\ and press ENTER.
  3. Type following command and press ENTER:
Appcmd set config "Default Web Site" /section:system.webServer/Security/requestFiltering -allowDoubleEscaping:True
  1. Restart IIS service by typing iisreset and pressing ENTER.
  2. Close the Command Prompt.

2.9 Subordinate Certificate Creation

Once the Subordinate CA has been configured and the request successfully generated, it is now time to complete the Subordinate CA Certificate by using the TFS-ROOT-CA Server.

  1. On the TFS-ROOT-CA Server insert the RootCAFiles Virtual Floppy Disk.
  2. Copy the A:\TFS-CA01.corp.tfslabs.com_corp-TFS-CA01-CA.req file to the C:\RootCA folder.
  3. On the TFS-ROOT-CA Server open Certification Authority Console (certsrv.msc).
  4. Right-click on the TFS Labs Certificate Authority Server, select All Tasks and click on Submit new request….
  5. Browse to the C:\RootCA folder and select the TFS-CA01.corp.tfslabs.com_corp-TFS-CA01-CA.req file that was copied from TFS-CA01. Click the Open button to continue.
  6. Once the request has been submitted, go to the Pending Requests folder to see the Certificate. It should be identified as Request ID 2, the first request being the Self-Signed Root Certificate (not shown).
  7. To issue the Certificate, right-click on the request, select All Tasks and click on Issue.
  8. Once the Certificate has been issued, go to the Issued Certificates folder to see the Certificate. It is still identified as Request ID 2. Double-click on the Certificate to open the Certificate Properties window.
  1. On the Details tab, click the Copy to File… button.
  2. On the first screen of the Certificate Export Wizard, click the Next button to continue.
  3. On the Export File Format screen, select the Cryptographic Message Syntax Standard – PKCS #7 Certificate (.P7B) format. Select the option to Include all certificates in the certification path if possible and click the Next button.
  4. For the file name, enter C:\RootCA\TFS Labs Enterprise CA.p7b and click Next to continue.
  5. Click the Finish button to complete the wizard.
  6. Copy the C:\RootCA\TFS Labs Enterprise CA.p7b file to the A:\ Drive.
  7. Eject the RootCAFiles Virtual Floppy Disk.
  8. On the TFS-CA01 Server insert the RootCAFiles Virtual Floppy Disk. Copy the A:\TFS Labs Enterprise CA.p7b file to root of the C:\ Drive.
  9. On the TFS-CA01 Server, open the Certification Authority Console (certsrv.msc).
  10. Right-click on the TFS Labs Enterprise CA Server, go to All Tasks and select the option to Install CA Certificate….
  11. Browse to the C:\ Drive and select the TFS Labs Enterprise CA.p7b file and click Open.
  12. If there were no errors in installing the Certificate, right-click on the TFS Labs Enterprise CA Server, go to All Tasks and click the Start Service option.
  13. The Subordinate Certificate has now been installed successfully, and the Subordinate Certificate Authority is now running.
  14. Eject the RootCAFiles Virtual Floppy Disk.

2.10 Set Maximum Certificate Age

Since all Certificates that will be created by the Subordinate CA will only be valid for 1 year, the setting can be forced so that a Certificate Template does not attempt to sign a Certificate for a longer time period.

  1. To define the maximum age of any Certificate that the Subordinate CA issues, run the following commands from an Administrative Command Prompt:
Certutil -setreg CA\ValidityPeriodUnits 1
Certutil -setreg CA\ValidityPeriod "Years"
  1. Once that is completed, restart the Active Directory Certificate Services service.

2.11 Subordinate Certificate Authority CDP and AIA Configuration

Before the Subordinate CA CDP and AIA Configuration can be added to the Subordinate Certificate, the CertEnroll folder in IIS will need to have Directory Browsing enabled:

  1. Open the Internet Information Services (IIS) Manager Console.
  2. On the Connections pane, expand TFS-CA01 and then expand Sites.
  3. In the Connections pane, under the Default Web Site, ensure the CertEnroll virtual directory is selected.
  4. In the CertData pane, double-click on Directory Browsing.
  5. In Actions pane click Enable.
  6. Close the Internet Information Services (IIS) Manager Console.

Once the Directory Browsing option has been enabled, the CDP and AIA entries can now be added:

  1. Open the Certification Authority Console (certsrv.msc).
  2. Right-click on TFS Labs Enterprise CA Server and select Properties.
  3. On the Extensions tab, verify that the CRL Distribution Point (CDP) extension is selected and click the Add button.
  4. Under the Location field, enter the following address and click the OK button:
http://pki.corp.tfslabs.com/CertEnroll/<CaName><CRLNameSuffix><DeltaCRLAllowed>.crl
  1. Back on the Extensions tab, verify that the Include in CRLs. Clients use this to find Delta CRL locations. and Include in the CDP extension of issued certificates options are selected for the location that was just entered.
  2. On the Extensions tab, verify that the Authority Information Access (AIA) extension is selected and click the Add button.
  3. Under the Location field, enter the following address and click the OK button:
http://pki.corp.tfslabs.com/CertEnroll/<ServerDNSName>_<CaName><CertificateName>.crt
  1. Back on the Extensions tab, verify that the Include in the AIA extension of issued certificates option is selected for the location that was just entered.
  2. Click the OK button to commit the changes. When prompted to restart Active Directory Certificate Services, click the Yes button.
  3. Verify that the settings are correct by running the following commands in an Administrative Command Prompt:
Certutil -getreg CA\CRLPublicationURLs
Certutil -getreg CA\CACertPublicationURLs
  1. In the Certification Authority Console, right-click on Revoked Certificates under TFS Labs Enterprise CA and select All Tasks > Publish.
  2. On the Publish CRL window, verify that New CRL is selected and click the OK button.

2.12 Enable Auditing on the Subordinate Certificate Authority

Auditing is needed on any Server running Active Directory Certificate Services. This will write logs to the Windows Event Log whenever a Certificate is issued or revoked.

  1. Open the Local Security Policy Console (secpol.msc) and modify the Security Settings > Local Policies > Audit Policy > Audit object access setting to audit Success and Failure.
  2. Enable auditing for the Certificate Authority by running the following command from an Administrative Command Prompt:
Certutil -setreg CA\AuditFilter 127
  1. Restart the Active Directory Certificate Services Service.

2.13 CPS Document Placeholders

Open the C:\inetpub\wwwroot folder and create a file called cps.html (C:\inetpub\wwwroot\cps.html). This is a very basic placeholder for the Certification Practice Statement that can be filled out later based on the requirements of your organization.

<html>
<head>
<title>TFS Labs Certification Practice Statement</title>
</head>
<body>
TFS Labs Certification Practice Statement
</body>
</html>

2.14 Verify PKI Infrastructure

Before continuing with the OCSP Role configuration and the deployment of the Root and Intermediate Certificates to the TFS Labs Domain, verify that there are no issues with the Active Directory Certificate Services Configuration:

  1. On the the TFS-CA01 Server, open the Enterprise PKI Console (PKIView.msc).
  2. Under the Enterprise PKI node, click on the TFS Labs Certificate Authority Server and check that the status of the CA, AIA and CDP is OK.

If there are no issues with the Enterprise PKI configuration, then the initial deployment is now complete.

2.15 Optional: Create Folder for Certificate Files

On the TFS-CA01 Server, create a folder that will be used to host the Root and Subordinate Certificate Files for ease of deployment to internal users:

  1. On the Root of the C:\ Drive, create a folder called Certificates (C:\Certificates).
  2. Open the Internet Information Services (IIS) Manager Console.
  3. On the Connections pane, expand TFS-CA01 and then expand Sites.
  4. Right-click on Default Web Site and select Add Virtual Directory.
  5. On Add Virtual Directory page, in Alias, enter Certificates. For the Physical path, enter C:\Certificates and then click OK.
  6. In the Connections pane, under the Default Web Site, ensure the Certificates virtual directory is selected.
  7. In the Certificates Home pane, double-click on Directory Browsing.
  8. In the Actions pane, click the Enable button.
  9. Close the Internet Information Services (IIS) Manager Console.

Once the PKI implementation is completed the necessary Certificate files will be available internally at this location:

http://pki.corp.tfslabs.com/Certificates/

Certificate Authority in Windows Server 2019

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