How to Grant permission to user on Certificate private key using powershell?

Question

Certificate is already installed on machine. Now I want to give read permission on PrivateKey of Certificate to application user.

Answer 1

Here is the Answer.

Created a powershell script file AddUserToCertificate.ps1

Here is the content for script file.

param(
    [string]$userName,
    [string]$permission,
    [string]$certStoreLocation,
    [string]$certThumbprint
);
# check if certificate is already installed
$certificateInstalled = Get-ChildItem cert:$certStoreLocation | Where thumbprint -eq $certThumbprint

# download & install only if certificate is not already installed on machine
if ($certificateInstalled -eq $null)
{
    $message="Certificate with thumbprint:"+$certThumbprint+" does not exist at "+$certStoreLocation
    Write-Host $message -ForegroundColor Red
    exit 1;
}else
{
    try
    {
        $rule = new-object security.accesscontrol.filesystemaccessrule $userName, $permission, allow
        $root = "c:\programdata\microsoft\crypto\rsa\machinekeys"
        $l = ls Cert:$certStoreLocation
        $l = $l |? {$_.thumbprint -like $certThumbprint}
        $l |%{
            $keyname = $_.privatekey.cspkeycontainerinfo.uniquekeycontainername
            $p = [io.path]::combine($root, $keyname)
            if ([io.file]::exists($p))
            {
                $acl = get-acl -path $p
                $acl.addaccessrule($rule)
                echo $p
                set-acl $p $acl
            }
        }
    }
    catch 
    {
        Write-Host "Caught an exception:" -ForegroundColor Red
        Write-Host "$($_.Exception)" -ForegroundColor Red
        exit 1;
    }    
}

exit $LASTEXITCODE

Now run it as part of deployment. Example to running above script in powershell console window.

C:\>.\AddUserToCertificate.ps1 -userName testuser1 -permission read -certStoreLocation \LocalMachine\My -certThumbprint 1fb7603985a8a11d3e85abee194697e9784a253

this example give read permission to user testuser1 on certificate that in installed in \\LocalMachine\\My and has thumb print 1fb7603985a8a11d3e85abee194697e9784a253

If you are using ApplicationPoolIdentity then you username will be 'IIS AppPool\\AppPoolNameHere'

Note : You will need to use ' ' as there is a space between IIS and AppPool.

Answer 2

The above answer did not work for me as the $_.privatekey returned null. I managed to get access to the private key and assign 'Read' permissions for my Application Pool as follows:

param (
[string]$certStorePath  = "Cert:\LocalMachine\My",
[string]$AppPoolName,
[string]$certThumbprint
)

Import-Module WebAdministration

$certificate = Get-ChildItem $certStorePath | Where thumbprint -eq $certThumbprint

if ($certificate -eq $null)
{
    $message="Certificate with thumbprint:"+$certThumbprint+" does not exist at "+$certStorePath
    Write-Host $message -ForegroundColor Red
    exit 1;
}else
{
    $rsaCert = [System.Security.Cryptography.X509Certificates.RSACertificateExtensions]::GetRSAPrivateKey($certificate)
    $fileName = $rsaCert.key.UniqueName
    $path = "$env:ALLUSERSPROFILE\Microsoft\Crypto\Keys\$fileName"
    $permissions = Get-Acl -Path $path

    $access_rule = New-Object System.Security.AccessControl.FileSystemAccessRule("IIS AppPool\$AppPoolName", 'Read', 'None', 'None', 'Allow')
    $permissions.AddAccessRule($access_rule)
    Set-Acl -Path $path -AclObject $permissions
}

Answer 3

It came to my attention a few weeks ago that something changed (I suspect a Windows update) and broke the ability for some certificates to use the CspKeyContainerInfo.UniqueKeyContainerName property referenced in Michael Armitage's script. Some sleuthing uncovered that Windows decided to start using CNG instead of Crypto Service Provider to protect the key. The following script fixed my issue and should correctly support CNG vs CSP use case scenarios:

$serviceUser = "DOMAIN\Service User"
$certificate = Get-ChildItem Cert:\LocalMachine\My | Where-Object Thumbprint -eq "certificatethumbprint"

$privateKey = [System.Security.Cryptography.X509Certificates.RSACertificateExtensions]::GetRSAPrivateKey($certificate)
$containerName = ""
if ($privateKey.GetType().Name -ieq "RSACng")
{
    $containerName = $privateKey.Key.UniqueName
}
else
{
    $containerName = $privateKey.CspKeyContainerInfo.UniqueKeyContainerName
}

$keyFullPath = $env:ProgramData + "\Microsoft\Crypto\RSA\MachineKeys\" + $containerName;
if (-Not (Test-Path -Path $keyFullPath -PathType Leaf))
{
    throw "Unable to get the private key container to set permissions."
}

# Get the current ACL of the private key
$acl = (Get-Item $keyFullPath).GetAccessControl()

# Add the new ACE to the ACL of the private key
$accessRule = New-Object System.Security.AccessControl.FileSystemAccessRule($serviceUser, "Read", "Allow")
$acl.AddAccessRule($accessRule);

# Write back the new ACL
Set-Acl -Path $keyFullPath -AclObject $acl;

You would, of course, want to adapt/enhance this to meet your specific needs.

Answer 4

As an alternate to above script. You can use PowerShell module. I have not tried it myself but module looks good. http://get-carbon.org/index.html

Here is command to set permissions http://get-carbon.org/Grant-Permission.html

Answer 5

You can use WinHttpCertCfg.exe, a Certificate Configuration Tool Link: https://docs.microsoft.com/en-us/windows/desktop/winhttp/winhttpcertcfg-exe--a-certificate-configuration-tool

Some code example:

Set privatekeyAcces to Svc-LocalAgent$@mydomain.local
*.\WinHttpCertCfg.exe -g -c LOCAL_MACHINE\MY -s *.d365.mydomain.com  -a "Svc-LocalAgent$@mydomain.com"*

Answer 6

Adding on Michael Armitage script, This will work for both the cases where PrivateKey value is present and when it is blank

function setCertificatePermission {
    param($accountName, $certificate)
    if([string]::IsNullOrEmpty($certificate.PrivateKey))
    {
        $rsaCert = [System.Security.Cryptography.X509Certificates.RSACertificateExtensions]::GetRSAPrivateKey($certificate)
        $fileName = $rsaCert.key.UniqueName
        $path = "$env:ALLUSERSPROFILE\Microsoft\Crypto\Keys\$fileName"
        $permissions = Get-Acl -Path $path
        $access_rule = New-Object System.Security.AccessControl.FileSystemAccessRule($accountName, 'FullControl', 'None', 'None', 'Allow')
        $permissions.AddAccessRule($access_rule)
        Set-Acl -Path $path -AclObject $permissions
    } else{
            $user = New-Object System.Security.Principal.NTAccount($accountName)
            $accessRule = New-Object System.Security.AccessControl.CryptoKeyAccessRule($user, 'FullControl', 'Allow')
            $store = New-Object System.Security.Cryptography.X509Certificates.X509Store("My","LocalMachine")
            $store.Open("ReadWrite")
            $rwCert = $store.Certificates | where {$_.Thumbprint -eq $certificate.Thumbprint}
            $csp = New-Object System.Security.Cryptography.CspParameters($rwCert.PrivateKey.CspKeyContainerInfo.ProviderType, $rwCert.PrivateKey.CspKeyContainerInfo.ProviderName, $rwCert.PrivateKey.CspKeyContainerInfo.KeyContainerName)
            $csp.Flags = "UseExistingKey","UseMachineKeyStore"
            $csp.CryptoKeySecurity = $rwCert.PrivateKey.CspKeyContainerInfo.CryptoKeySecurity
            $csp.KeyNumber = $rwCert.PrivateKey.CspKeyContainerInfo.KeyNumber
            $csp.CryptoKeySecurity.AddAccessRule($AccessRule)
            $rsa2 = New-Object System.Security.Cryptography.RSACryptoServiceProvider($csp)
            $store.close()
        }
}