(Visual Basic 6.0) Extract PKCS7 Signature Digest

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

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

Dim crypt As New ChilkatCrypt2

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

' First let's see if this .p7m signature can be verified, and the original file extracted.
Dim verified As Long
verified = crypt.VerifyP7M(p7mFile,outPath)
If (verified <> 1) Then
    Debug.Print crypt.LastErrorText
    Exit Sub
End If

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

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

Dim bHaveBase64 As Long
bHaveBase64 = 0
If (sbBase64.ContentsEqual("4D49",1) = 1) Then
    bHaveBase64 = 1
    sbBase64.Clear 
    success = sbBase64.AppendBd(pkcs7Data,"utf-8",0,0)
End If

' Get each signer's signature digest.
crypt.EncodingMode = "base64"
Dim i As Long
i = 0
Dim digest As String
Do 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 <> 1) Then
        Debug.Print crypt.LastErrorText
        Exit Sub
    End If

    Debug.Print "Signer " & (i + 1) & " digest = " & digest
    i = i + 1
Loop