DataFlex

Verify DKIM Signatures in a Message

Demonstrates the Chilkat Dkim.DkimVerify method, which verifies the DKIM-Signature at a given zero-based index in a MIME message. The arguments are the signature index and a BinData holding the complete MIME. This example loops over every signature and reads the JSON VerifyInfo after each.

Tip: JSON parsing code for the VerifyInfo result can be generated at Chilkat Tools.

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: Verifying confirms two things at once: that the message was signed by the claimed domain, and that the signed headers and body have not been altered since. Chilkat uses a cached public key when the selector and domain match one you loaded, and otherwise fetches it from DNS. The message is not modified. After each call, the VerifyInfo JSON records the details — selector, domain, and outcome — which is what you would log or surface when a signature fails. Verification is per-signature, so a message with several signatures may have some pass and others fail.

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Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoDkim
    Variant vMimeData
    Handle hoMimeData
    Integer iNumSigs
    Integer i
    String sTemp1

    Move False To iSuccess

    //  Demonstrates the Dkim.DkimVerify method, which verifies the DKIM-Signature at a given index in
    //  a MIME message.  The 1st argument is the zero-based signature index and the 2nd is a BinData
    //  holding the complete MIME.

    Get Create (RefClass(cComChilkatDkim)) To hoDkim
    If (Not(IsComObjectCreated(hoDkim))) Begin
        Send CreateComObject of hoDkim
    End

    //  Load the received MIME message.
    Get Create (RefClass(cComChilkatBinData)) To hoMimeData
    If (Not(IsComObjectCreated(hoMimeData))) Begin
        Send CreateComObject of hoMimeData
    End
    Get ComLoadFile Of hoMimeData "qa_data/received.eml" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoMimeData To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    //  A message may carry more than one DKIM signature.  Verify each in turn.  Signatures are
    //  indexed in top-to-bottom header order.
    Get pvComObject of hoMimeData to vMimeData
    Get ComNumDkimSigs Of hoDkim vMimeData To iNumSigs

    For i From 0 To (iNumSigs - 1)
        //  DkimVerify uses a cached public key when one matches the signature's selector and domain;
        //  otherwise it retrieves the key from DNS.
        Get pvComObject of hoMimeData to vMimeData
        Get ComDkimVerify Of hoDkim i vMimeData To iSuccess
        If (iSuccess = True) Begin
            Showln "Signature " i ": verified."
        End
        Else Begin
            Showln "Signature " i ": verification failed."
        End

        //  VerifyInfo contains JSON describing the most recent DkimVerify call (selector, domain,
        //  result, and so on).
        Get ComVerifyInfo Of hoDkim To sTemp1
        Showln sTemp1
        //  JSON parsing code for this result can be generated at Chilkat's online tool:
        //  https://tools.chilkat.io/jsonParse
    Loop



End_Procedure