(VB.NET) Extract PKCS7 Signature Digest

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

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

Dim crypt As New Chilkat.Crypt2

Dim p7mFile As String = "qa_data/p7m/test.pdf.p7m"
Dim outPath As String = "qa_output/test.pdf"

' First let's see if this .p7m signature can be verified, and the original file extracted.
Dim verified As Boolean = crypt.VerifyP7M(p7mFile,outPath)
If (verified <> True) Then
    Debug.WriteLine(crypt.LastErrorText)
    Exit Sub
End If


' How many signers?
' (The NumSignerCerts property is set whenever a signature is verified.)
Debug.WriteLine("Num Signers: " & crypt.NumSignerCerts)

' Load the .p7m into memory...
Dim pkcs7Data As New 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.
Dim sbBase64 As New Chilkat.StringBuilder
Dim hexStr As String = pkcs7Data.GetEncodedChunk(0,2,"hex")
sbBase64.Append(hexStr)

Dim bHaveBase64 As Boolean = False
If (sbBase64.ContentsEqual("4D49",True) = True) Then
    bHaveBase64 = True
    sbBase64.Clear()
    sbBase64.AppendBd(pkcs7Data,"utf-8",0,0)
End If


' Get each signer's signature digest.
crypt.EncodingMode = "base64"
Dim i As Integer = 0
Dim digest As String
While i < crypt.NumSignerCerts
    If (bHaveBase64) Then
        digest = crypt.Pkcs7ExtractDigest(i,sbBase64.GetAsString())
    Else
        digest = crypt.Pkcs7ExtractDigest(i,pkcs7Data.GetEncoded("base64"))
    End If

    If (crypt.LastMethodSuccess <> True) Then
        Debug.WriteLine(crypt.LastErrorText)
        Exit Sub
    End If

    Debug.WriteLine("Signer " & (i + 1) & " digest = " & digest)
    i = i + 1
End While