(VB.NET) Verify Opaque Signature and Retrieve Signing Certificates

Demonstrates how to verify a PCKS7 opaque digital signature (signed data), extract the original file/data, and then extract the certificate(s) that were used to sign.

Note: This example requires Chilkat v11.0.0 or greater.

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Dim success As Boolean = False

' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim crypt As New Chilkat.Crypt2

' Verify a PKCS7 signed-data (opaque signature) file and extract the original content to a file.
success = crypt.VerifyP7M("qa_data/p7m/opaqueSig.p7","qa_output/originalData.dat")
If (success = False) Then
    Debug.WriteLine(crypt.LastErrorText)
    Exit Sub
End If


' Alternatively, we can do it in memory...
Dim binData As New Chilkat.BinData
success = binData.LoadFile("qa_data/p7m/opaqueSig.p7")
' Your app should check for success, but we'll skip the check for brevity..

' If verified, the signature is unwrapped and binData is replaced with the original data that was signed.
success = crypt.OpaqueVerifyBd(binData)
If (success = False) Then
    Debug.WriteLine(crypt.LastErrorText)
    Exit Sub
End If


' For our testing, we signed some text, so we can get it from the binData..
Debug.WriteLine("Original Data:")
Debug.WriteLine(binData.GetString("utf-8"))

' After any method call that verifies a signature, the crypt object will contain the certificate(s)
' that were used for signing (assuming the X.509 certs were available in the signature, which is typically the case).

' Get each signing certificate, and build the certificate chain for each.
Dim cert As New Chilkat.Cert
Dim certChain As New Chilkat.CertChain
Dim numCerts As Integer = crypt.NumSignerCerts
Dim i As Integer = 0
While i < numCerts
    crypt.LastSignerCert(i,cert)
    Debug.WriteLine(cert.SubjectDN)

    success = cert.BuildCertChain(certChain)
    If (success = False) Then
        Debug.WriteLine(cert.LastErrorText)
        Exit Sub
    End If


    i = i + 1
End While