Reporting on Digitally Signed Files with PowerShell

Wondering how to find Digitally Signed Files with PowerShell? We can help you.

When there are many new files that are digitally signed with a certificate, we will at times need to check the status of the Digital Signatures of these files.

For this, we can use, the PowerShell ‘Get-AuthenticodeSignature’ cmdlet.

Here at Bobcares, we use PowerShell for reporting on Digitally Signed files for our customers as a part of Server Management Services.

Checking properties of Digitally Signed Files with PowerShell

These Cmdlets will examine a file and show the properties of the Digital Certificate on a file.

Here is an example of it:

PS C:\> Get-AuthenticodeSignature -FilePath C:\windows\notepad.exe

Directory: C:\windows

SignerCertificate Status Path
----------------- ------ ----
AE9C1AE54763822EEC42474983D8B635116C8452 Valid notepad.exe

A quick glance shows us the file has a valid digital signature.

For checking more details, we can pipe the results into Format-List using the following:

C:\> Get-AuthenticodeSignature -FilePath C:\windows\notepad.exe | Format-List

It is possible to take a list of files, pipe them in to see their status using the following:

C:\> get-childitem c:\windows\*.exe | Get-AuthenticodeSignature

However, the Cmdlet has a particular format.

If we try to take this information and export it as a list to a CSV to report on a list of files, it will not give a clear result.

First, we will see the exposed ones using Get-Member using the following command:

C:\> get-childitem c:\windows\*.exe | Get-AuthenticodeSignature | Get-Member

We can run the Get-AuthenticodeSignature and take only the correct ones and output them to a CSV file we can use the following:

Get-ChildItem c:\windows\notepad*.exe | Get-AuthenticodeSignature | ` Select-Object -Property Path,ISOSBinary,SignatureType,Status,StatusMessage | ` Export-CSV C:\report\Signature.csv -NoTypeInformation

This will provide a more clear result.

We can see the properties *IN* that X509Certificate2 object by using the following:

Get-ChildItem c:\windows\notepad*.exe | Get-AuthenticodeSignature | ` Select-Object -ExpandProperty SignerCertificate | Get-Member -MemberType Properties

To obtain a property such as the SerialNumber, we will use a feature of Select-Object called a “Calculated Property”.

Get-ChildItem C:\Windows\notepad.exe | Get-AuthenticodeSignature | ` Select-Object -Property @{Name=’SignerSerialNumber’;Expression={($_.SignerCertificate.SerialNumber)}}

Using this in PowerShell  will produce the following result:

SignerSerialNumber —————— 33000001C422B2F79B793DACB20000000001C4

For producing a Calculated Property for each of the individual items from the X509Certificate2 object we can use the following:

Get-ChildItem C:\Windows\notepad.exe | Get-AuthenticodeSignature | ` Select-object -Property Path, Status,StatusMessage,SignatureType, ` @{Name=’SubjectName’;Expression={($_.SignerCertificate.Subject)}}, ` @{Name=’SubjectIssuer’;Expression={($_.SignerCertificate.Issuer)}}, ` @{Name=’SubjectSerialNumber’;Expression={($_.SignerCertificate.SerialNumber)}}, ` @{Name=’SubjectNotBefore’;Expression={($_.SignerCertificate.NotBefore)}}, ` @{Name=’SubjectNotAfter’;Expression={($_.SignerCertificate.NotAfter)}}, ` @{Name=’SubjectThumbprint’;Expression={($_.SignerCertificate.ThumbPrint)}}, ` @{Name=’TimeStamperName’;Expression={($_.SignerCertificate.Subject)}}, ` @{Name=’TimeStamperIssuer’;Expression={($_.SignerCertificate.Issuer)}}, ` @{Name=’TimeStamperSerialNumber’;Expression={($_.SignerCertificate.SerialNumber)}}, ` @{Name=’TimeStamperNotBefore’;Expression={($_.SignerCertificate.NotBefore)}}, ` @{Name=’TimeStamperNotAfter’;Expression={($_.SignerCertificate.NotAfter)}}, ` @{Name=’TimeStamperThumbprint’;Expression={($_.SignerCertificate.ThumbPrint)}}

With this, we now have an object that would export directly to a CSV.

We can also write a function corresponding to this as given below:

Function Expand-AuthenticodeSignature($AuthenticodeSignature) { $AuthenticodeSignature | Select-object -Property Path, ` Status,StatusMessage,SignatureType, ` @{Name=’SubjectName’;Expression={($_.SignerCertificate.Subject)}}, ` @{Name=’SubjectIssuer’;Expression={($_.SignerCertificate.Issuer)}}, ` @{Name=’SubjectSerialNumber’;Expression={($_.SignerCertificate.SerialNumber)}}, ` @{Name=’SubjectNotBefore’;Expression={($_.SignerCertificate.NotBefore)}}, ` @{Name=’SubjectNotAfter’;Expression={($_.SignerCertificate.NotAfter)}}, ` @{Name=’SubjectThumbprint’;Expression={($_.SignerCertificate.ThumbPrint)}}, ` @{Name=’TimeStamperName’;Expression={($_.SignerCertificate.Subject)}}, ` @{Name=’TimeStamperIssuer’;Expression={($_.SignerCertificate.Issuer)}}, ` @{Name=’TimeStamperSerialNumber’;Expression={($_.SignerCertificate.SerialNumber)}}, ` @{Name=’TimeStamperNotBefore’;Expression={($_.SignerCertificate.NotBefore)}}, ` @{Name=’TimeStamperNotAfter’;Expression={($_.SignerCertificate.NotAfter)}}, ` @{Name=’TimeStamperThumbprint’;Expression={($_.SignerCertificate.ThumbPrint)}}}

Now that we have the data in a more consumable and exportable form. We can get a list of files with their Digital Certificate status using the following:

$List=Get-ChildItem C:\Windows\*.exe | Get-AuthenticodeSignature

After that, we can produce the new output in a script with our function and Export it directly to a CSV file.

Expand-AuthenticodeSignature -AuthenticodeSignature $List | Export-Csv C:\report\working.csv

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Conclusion

To conclude we saw how our Support Techs implement reporting on digitally signed files with PowerShell.