Unsign an assembly by tweaking the IL code before assembling it again.

unsign.ps1

[cmdletbinding()]
param($assembly, [switch]$DisplaySigningOnly)

$fullpath = [System.IO.Path]::GetFullPath($assembly)
$dir = [System.IO.Path]::GetDirectoryName($fullpath)
$ext = [System.IO.Path]::GetExtension($fullpath)
$filename = [System.IO.Path]::GetFileNameWithoutExtension($fullpath)

$assemblyBackupPath = [System.IO.Path]::Combine($dir, $filename + ".signed" + $ext)
$assemblyBackupDir = [System.IO.Path]::Combine($dir, "original")

$dasmFile = "$($env:TEMP)/$assembly.dasm.il"
$unsignedFile = "$($env:TEMP)/$assembly.unsigned.il"


function getSigningInfo
{
    param($fn)
    $out = sn /vf $fn

    if ($out -match 'does not represent a strongly named assembly') { return "unsigned" }
    if ($out -match 'delay-signed or test-signed assembly') { return "delaysigned" }
    if ($out -match 'is valid') { return "signed" }
}

try
{
    $signinfo = getSigningInfo $assembly
    Write-Host "Processing $assembly : $signinfo" -ForegroundColor Green
    if ($DisplaySigningOnly)
    {
        exit
    }

    if (($signinfo -eq "signed") -or ($signinfo -eq "unsigned"))
    {
        Write-Host "Skip."
        exit
    }

    $Error.Clear()
    Write-Host "Disassemble $assembly" -ForegroundColor Green
    ildasm $assembly /out:$dasmFile
    $il = [System.IO.File]::ReadAllText($dasmFile)

    Write-Host "Removing signing..." -ForegroundColor Green
    $unsigned = [regex]::Replace(
        $il, 
        "(^  \.publickey =.+$\n.+\n.+\n.+\n.+\n.+\n.+\n.+\n.+\n.+\n)", 
        "",
        [System.Text.RegularExpressions.RegexOptions]::Multiline)

    Write-Host "Writing to $unsignedFile" -ForegroundColor Green
    $unsigned | Out-File -Encoding utf8 $unsignedFile

    Write-Host "Backing up $assembly to $assemblyBackupDir" -ForegroundColor Green
    mkdir -Force $assemblyBackupDir -ErrorAction Stop > $null

    if ($Error.Count -ge 1) 
    {
        Write-Host "Something went wrong" -ForegroundColor Red
        exit
    }

    move $assembly $assemblyBackupPath -Force -ErrorAction Stop

    Write-Host "Updating $assembly" -ForegroundColor Green
    if ($ext -ieq ".dll")
    {
        ilasm.exe $unsignedFile /dll /output=$assembly > $null
    }
    else
    {
        ilasm.exe $unsignedFile /output=$assembly > $null
    }
}
finally
{
    del $dasmFile -ErrorAction SilentlyContinue
    del $unsignedFile -ErrorAction SilentlyContinue
}