Windows Server Validate certificate chain with powershell

ChatGPT said:

When working with certificates in PowerShell and trying to uniquely identify the issuer certificate to validate the certificate chain, you can use the Thumbprint property, which is not always unique and can lead to multiple matches for certificates with the same issuer name.

To uniquely identify the issuer certificate, you can use the SubjectKeyId property, also known as Authority Key Identifier. This property contains the key ID of the issuer's certifying authority. By matching the SubjectKeyId of the certificate with the Authority Key Identifier of the issuer certificate, you can uniquely identify the issuer certificate.

Here is an alternative approach using the Authority Key Identifier to find the issuer certificate:

Code:

# Retrieve the Authority Key Identifier of the certificate
$CertificateAuthorityKeyId = $Certificate.Extensions | Where-Object { $_.Oid.FriendlyName -eq "Authority Key Identifier" }

# Get the issuer certificate using the Authority Key Identifier
$IssuerCertificate = Get-ChildItem -Recurse -Path Cert: | Where-Object {
    $_.Extensions.Extension.Oid.FriendlyName -eq "Subject Key Identifier" -and
    $_.Extensions.Extension.Format(0).RawData -eq $CertificateAuthorityKeyId.Format(0).RawData
}

This script fetches the Authority Key Identifier of the certificate and then uses it to find the corresponding issuer certificate based on the Subject Key Identifier extension. This method helps in uniquely identifying the issuer certificate even when multiple certificates have the same issuer name.
Gatwick to Canterbury
Validating the certificate chain involves checking the expiration of each certificate in the chain to ensure none of them are expired. You can achieve this by comparing the NotAfter property of each certificate in the chain with the current date.

Let me know if you need further assistance or if there are any specific requirements for validating the certificate chain in PowerShell.

Click to expand...

1. Find the Issuer Certificate:
   
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   function Get-IssuerCertificate {<br> param (<br> [Parameter(Mandatory = $true)]<br> [System.Security.Cryptography.X509Certificates.X509Certificate2]$Certificate<br> )<br><br> $issuerName = $Certificate.Issuer<br> $issuerSerialNumber = $Certificate.SerialNumber<br><br> Get-ChildItem -Recurse -Path Cert: | Where-Object {<br> $.Issuer -eq $issuerName -and $.SerialNumber -eq $issuerSerialNumber<br> }<br>}<br>
2. Validate the Certificate Chain and Find the Closest-to-Expiration Certificate:
   
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   function Get-NearestExpirationCertificate {<br> param (<br> [Parameter(Mandatory = $true)]<br> [System.Security.Cryptography.X509Certificates.X509Certificate2]$Certificate<br> )<br><br> $chain = New-Object System.Security.Cryptography.X509Certificates.X509Chain<br> $chain.Build($Certificate)<br><br> $nearestExpirationCertificate = $null<br> $nearestExpirationDate = [datetime]::MaxValue<br><br> foreach ($element in $chain.ChainElements) {<br> $cert = $element.Certificate<br> if ($cert.NotAfter -lt $nearestExpirationDate) {<br> $nearestExpirationDate = $cert.NotAfter<br> $nearestExpirationCertificate = $cert<br> }<br> }<br><br> $nearestExpirationCertificate<br>}<br>

Key Steps in the Approach:​

1. Get the Issuer Certificate: Your function Get-IssuerCertificate is well-structured for retrieving the correct issuer using the issuer name and serial number. This will help ensure that you're identifying the specific certificate without confusion from other certificates that might share the same issuer name. Here’s how your function is structured:
   Code:

   powershell function Get-IssuerCertificate { param ( [Parameter(Mandatory = $true)] [System.Security.Cryptography.X509Certificates.X509Certificate2]$Certificate ) $issuerName = $Certificate.Issuer $issuerSerialNumber = $Certificate.SerialNumber Get-ChildItem -Recurse -Path Cert: | Where-Object { $_.Issuer -eq $issuerName -and $_.SerialNumber -eq $issuerSerialNumber } }

2. Find the Closest-to-Expiration Certificate: The Get-NearestExpirationCertificate function should serve well to walk through the chain and find the certificate that is nearest to expiration. This helps in quickly identifying potential risks in the certificate chain. Here’s your function for finding the nearest expiration certificate:
   Code:

   powershell function Get-NearestExpirationCertificate { param ( [Parameter(Mandatory = $true)] [System.Security.Cryptography.X509Certificates.X509Certificate2]$Certificate ) $chain = New-Object System.Security.Cryptography.X509Certificates.X509Chain $chain.Build($Certificate) $nearestExpirationCertificate = $null $nearestExpirationDate = [datetime]::MaxValue foreach ($element in $chain.ChainElements) { $cert = $element.Certificate if ($cert.NotAfter -lt $nearestExpirationDate) { $nearestExpirationDate = $cert.NotAfter $nearestExpirationCertificate = $cert } } $nearestExpirationCertificate }