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To bring your AD CS infrastructure forward to secure standards, you want to use the modern KSP and SHA-2. These standards are included as part of Microsoft's Cryptography API: Next Generation (CNG). You will need a Windows Server 2012 operating system or higher to take full advantage of KSP and SHA-2.
In the walkthrough below, we have a Windows Server 2019 Certificate Authority running certificate services using the traditional CSP and SHA-1. While newer Windows Server operating systems will default to the latest standards, Certificate Services may have been migrated from a legacy Windows Server operating system and may have retained the original settings.
If your AD CS is already using KSP and you only need to update them from SHA-1 to SHA-2, you can skip the section about CSP to KSP migration and jump directly to "Migrating the CA hash algorithm to SHA-2." This might be the case if your CA is running on a Windows Server 2012 server.
Back Up the CA
Before making significant changes to any part of your infrastructure, you want to have good backups. Making changes to AD CS is no exception. To back up the CA, use the following commands (depending on the OS level):
- Windows Server 2012 R2 & higher: Backup-CARoleService –path C:\CA-Backup -Password (Read-Host -Prompt "Enter Password" -AsSecureString)
- Windows Server 2012: Certutil –backup C:\CA-Backup
After running the command, verify that you have files as expected in the backup folder.
Next, we want to back up the registry on the CA. To do that, run the following command:
- reg export HKLM\SYSTEM\CurrentControlSet\services\CertSvc c:\<Backup directory>\CAregistry.reg
After exporting the registry, we can stop the CS service. To do so, run the following command from an administrator prompt:
Get the CA certificate details
Next, we want to view the details of our CA certificates. An easy way to do this is to export the details to a text file, which makes it easy to copy and paste certificate information as needed. Run the following command:
certutil -store my <your CA common name> > output.txt
The next step involves deleting the existing CA certificate and private key. Yes, delete it. We already have a backup, so doing this is safe. However, we can verify a few things. Run the following commands:
cd cert:\localmachine\my ls
From here, compare the values in the output text file created earlier with the details found in the command line. We can see that the thumbprints are the same.
This thumbprint value is the identity of the certificate we need to delete.
Migrate the CA certificate and private key to a KSP
Now, we can migrate the CA certificate and private key to the newer KSP. To do so, run a command from the command line, and import the CA certificate that we exported at the beginning. Next, the command changes the CSP to the Microsoft Software KSP.
Certutil –csp Microsoft Key Storage Provider -importpfx <Your backup directory .p12 key file>
Next, we want to export the certificate as a PFX file from the KSP.
Certutil –exportpfx my <CA Common Name> <CA Backup directory>\backupfile.pfx
Restore the PFX file using the command below:
Certutil -restorekey c:\<backup directory>\<CA common name>\your backup.pfx
Import registry settings for the CSP
First, verify that the CA indeed uses SHA-1 as the hash algorithm. Use the following command to do so:
Certutil –v –getreg ca\csp\HashAlgorithm
We now need to create two registry files to import to the CA. The first imports the hash algorithm settings to the CA.
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\<your CA common name\CSP] "ProviderType"=dword:00000000 "Provider"="Microsoft Software Key Storage Provider" "CNGPublicKeyAlgorithm"="RSA" "CNGHashAlgorithm"="SHA1"
Next, do the same thing for the encryption algorithm. Verify that your CA uses 3DES encryption. Use the following command to verify the encryption algorithm used:
certutil -v -getreg ca\encryptioncsp\EncryptionAlgorithm
Create a registry key with the following contents, replacing your CA server's common name:
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\<your CA common name>\EncryptionCSP] "ProviderType"=dword:00000000 "Provider"="Microsoft Software Key Storage Provider" "CNGPublicKeyAlgorithm"="RSA" "CNGEncryptionAlgorithm"="3DES" "MachineKeyset"=dword:00000001 "SymmetricKeySize"=dword:000000a8
Save the file and merge it into the registry.
Migrating the CA hash algorithm to SHA-2
The process of changing to the SHA256 encryption algorithm is fairly straightforward. We can do this with the certutil command:
certutil -setreg ca\csp\CNGHashAlgorithm SHA256
Even after running the above command, the root certificate is still SHA-1.
Hence, we need to renew the certificate. This is not mandatory but is recommended. The new root certificate does not replace the existing one, which will continue to validate all previously issued certificates. They can also chain up to the new root certificate as long as you keep the existing key pair.
Choose Renew CA Certificate under All Tasks for your AD CS CA.
To continue with this operation, confirm the restart of the services. Next, you will be prompted to regenerate the signing key. In most cases, you will not generate a new key pair.
After renewing the certificates, you can check the new root certificate in the certificate store and verify that you now see SHA256 for the signature algorithm and hash algorithm.
To finalize, Active Directory CS needs to be restarted.
Start CS and verify the settings
After importing the registry keys, we are in a position to start AD CS. Ping the service, and verify the provider and hash algorithm. Note the following commands:
Start-service certsvc Certutil -ping Certutil -getreg ca\csp\Provider Certutil -getreg ca\csp\CNGHashAlgorithm
As shown below, we now see both the provider and the hash algorithm reflecting the Microsoft Software KSP and SHA256.
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As shown, the process is tedious but straightforward to migrate from the legacy Microsoft Software CSP and SHA-1 to the newer Microsoft Software KSP and SHA256. However, this is a worthwhile endeavor, as it helps to strengthen the internal PKI infrastructure and cybersecurity posture of internal certificate services hosted by AD CS.