PureBasic

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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IncludeFile "CkCert.pb"
IncludeFile "CkMime.pb"

Procedure ChilkatExample()

    success.i = 0

    mime.i = CkMime::ckCreate()
    If mime.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkMime::ckLoadMimeFile(mime,"qa_data/signed.eml")
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        ProcedureReturn
    EndIf

    ;  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.
    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadFromFile(cert,"qa_data/signer.cer")
    If success = 0
        Debug CkCert::ckLastErrorText(cert)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    success = CkMime::ckSetVerifyCert(mime,cert)
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    ;  Now verify using the supplied certificate.
    success = CkMime::ckVerify(mime)
    If success <> 1
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    Debug "Signature verified using the supplied certificate."


    CkMime::ckDispose(mime)
    CkCert::ckDispose(cert)


    ProcedureReturn
EndProcedure