How to extract digest algorithm from signed dll using PowerShell?

Question

I have a dll file which is digitally signed. I need to write a PowerShell command which could get me the Digest Algorithm that is used for the Digital Signature.

Digest Algorithm info I need:

I tried with Get-AuthenticodeSignature but this didn't get me the Digest Algorithm info.

After running the following command I get the below result.

Get-AuthenticodeSignature "C:\Program Files\Application Verifier\vrfauto.dll" | Format-List

Results of above:

Answer 1

So what you are looking for is

Get-AuthenticodeSignature | %{
    $_.SignerCertificate.SignatureAlgorithm.FriendlyName
}

Lets go over how we got to there. First i find a file that has a Digital Signature. I will use PowerShell-6.1.2-win-x64.msi for this example.

Get-AuthenticodeSignature -FilePath C:\test\PowerShell-6.1.2-win-x64.msi | get-member

We see there is a object for the SignerCertificate

SignerCertificate      Property   System.Security.Cryptography.X509Certificates.X509Certificate2 SignerCertificate {get;}

So lets see what that holds

Get-AuthenticodeSignature -FilePath C:\test\PowerShell-6.1.2-win-x64.msi | %{
    $_.SignerCertificate | get-member
}

Now we see there is a SignatureAlgorithm property

SignatureAlgorithm              Property       System.Security.Cryptography.Oid SignatureAlgorithm {get;}

Now we dig one more deep

Get-AuthenticodeSignature -FilePath C:\test\PowerShell-6.1.2-win-x64.msi | %{
    $_.SignerCertificate.SignatureAlgorithm | get-member
}

We get :

FriendlyName Property   string FriendlyName {get;set;}
Value        Property   string Value {get;set;}

We can see there both strings so we test out which is better for us...turns out its friendly name :

Get-AuthenticodeSignature -FilePath C:\test\PowerShell-6.1.2-win-x64.msi | %{
    $_.SignerCertificate.SignatureAlgorithm.FriendlyName
}

Returns

sha256RSA