VB.NET

Check if an Email Was Received Digitally Signed

Demonstrates the read-only Chilkat Email.ReceivedSigned property, which is true if the email was originally received carrying one or more digital signatures. Knowing a message was signed is separate from knowing the signature checked out, so this example also reads SignaturesValid to report whether the signed content verified.

Background: A digital signature on an email (S/MIME) provides two things: authenticity (it was really sent by the holder of a particular certificate) and integrity (the content was not altered in transit). The sender signs a hash of the message with their private key; the recipient verifies it with the sender's public certificate. ReceivedSigned simply tells you a signature is present — verifying it is a separate step exposed through SignaturesValid.

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VB.NET

Dim success As Boolean = False

'  Demonstrates the read-only Email.ReceivedSigned property, which is true if this
'  email was originally received with a digital signature.  Use SignaturesValid to
'  determine whether the signed content actually verified.

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
    Debug.WriteLine("This email was received with a digital signature.")
    If (email.SignaturesValid = True) Then
        Debug.WriteLine("All signatures are valid.")
    Else
        Debug.WriteLine("One or more signatures are NOT valid.")
    End If

Else
    Debug.WriteLine("This email was not signed.")
End If


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