(PowerShell) Extract PKCS7 Signature Digest

Demonstrates how to extract a signature digest from a PKCS7 signature.

Chilkat .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This example requires the Chilkat Crypt API to have been previously unlocked.
# See Unlock Chilkat Crypt for sample code.

$crypt = New-Object Chilkat.Crypt2

$p7mFile = "qa_data/p7m/test.pdf.p7m"
$outPath = "qa_output/test.pdf"

# First let's see if this .p7m signature can be verified, and the original file extracted.
$verified = $crypt.VerifyP7M($p7mFile,$outPath)
if ($verified -ne $true) {
    $($crypt.LastErrorText)
    exit
}

# How many signers?
# (The NumSignerCerts property is set whenever a signature is verified.)
$("Num Signers: " + $crypt.NumSignerCerts)

# Load the .p7m into memory...
$pkcs7Data = New-Object Chilkat.BinData
$pkcs7Data.LoadFile($p7mFile)

# Check to see if this .p7m contains the binary bytes, or if it's
# already base64 encoded.  Get the 1st two bytes.  If the first two 
# bytes are the us-ascii values "MI", then we have base64.
$sbBase64 = New-Object Chilkat.StringBuilder
$hexStr = $pkcs7Data.GetEncodedChunk(0,2,"hex")
$sbBase64.Append($hexStr)

$bHaveBase64 = $false
if ($sbBase64.ContentsEqual("4D49",$true) -eq $true) {
    $bHaveBase64 = $true
    $sbBase64.Clear()
    $sbBase64.AppendBd($pkcs7Data,"utf-8",0,0)
}

# Get each signer's signature digest.
$crypt.EncodingMode = "base64"
$i = 0

while ($i -lt $crypt.NumSignerCerts) {
    if ($bHaveBase64) {
        $digest = $crypt.Pkcs7ExtractDigest($i,$sbBase64.GetAsString())
    }
    else {
        $digest = $crypt.Pkcs7ExtractDigest($i,$pkcs7Data.GetEncoded("base64"))
    }

    if ($crypt.LastMethodSuccess -ne $true) {
        $($crypt.LastErrorText)
        exit
    }

    $("Signer " + $i + 1 + " digest = " + $digest)
    $i = $i + 1
}