B4X

Supply a Fallback Certificate for S/MIME Verification

Demonstrates the Chilkat Mime.SetVerifyCert method, which supplies a signer-certificate fallback for subsequent signature verification. The only argument is the Cert.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: Most signed messages embed the signer's certificate, so Verify can find it automatically. But some signatures omit it to save space, expecting the recipient to already have it. This method provides that certificate as a fallback so verification can proceed — the S/MIME equivalent of already knowing the sender's public key out of band.

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Dim success As Boolean = False

Dim mime As ChilkatMime
mime.Initialize
success = mime.LoadMimeFile("qa_data/signed.eml")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


'  Supply a signer-certificate fallback for verification.  This is useful when the signature does
'  not embed the signer certificate and Chilkat cannot otherwise locate it.
Dim cert As ChilkatCert
cert.Initialize("cert")
success = cert.LoadFromFile("qa_data/signer.cer")
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


success = mime.SetVerifyCert(cert)
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


'  Now verify using the supplied certificate.
success = mime.Verify
If success <> True Then
    Log(mime.LastErrorText)
    Return
End If

Log("Signature verified using the supplied certificate.")