VB.NET

Verify the Digital Signatures on an Email

Demonstrates the read-only Chilkat Email.SignaturesValid property, which is true when the email was received with one or more digital signatures and all of them validated, indicating the message was not altered. It is only meaningful when ReceivedSigned is true, so this example checks that first.

Background: A valid signature proves integrity — the bytes that were signed are exactly the bytes you received — but that is not the same as trust. A message can carry a perfectly valid signature from a certificate you have no reason to trust (self-signed, expired, or from an unknown issuer). So after confirming SignaturesValid, an application that needs assurance of who signed should separately examine the signer certificate and its chain (see LastSignerCert).

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Dim success As Boolean = False

'  Demonstrates the read-only Email.SignaturesValid property, which is true if the email
'  was received with one or more digital signatures AND all of them validated (indicating
'  the email was not altered).  It is only meaningful when ReceivedSigned is true.

Dim email As New Chilkat.Email

success = email.LoadEml("qa_data/eml/signed.eml")
If (success = False) Then
    Debug.WriteLine(email.LastErrorText)
    Exit Sub
End If


If (email.ReceivedSigned = True) Then
    If (email.SignaturesValid = True) Then
        Debug.WriteLine("The signature(s) verified: the email was not altered.")
    Else
        Debug.WriteLine("Signature verification FAILED.")
    End If

Else
    Debug.WriteLine("This email was not received with a digital signature.")
End If


'  Note: Paths such as "qa_data/..." are relative local filesystem paths,
'  relative to the current working directory of the running application.