PowerBuilder

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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integer li_rc
integer li_Success
oleobject loo_Dkim
oleobject loo_MimeData
integer li_NumSigs
integer i

li_Success = 0

//  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.

loo_Dkim = create oleobject
li_rc = loo_Dkim.ConnectToNewObject("Chilkat.Dkim")
if li_rc < 0 then
    destroy loo_Dkim
    MessageBox("Error","Connecting to COM object failed")
    return
end if

//  Load the received MIME message.
loo_MimeData = create oleobject
li_rc = loo_MimeData.ConnectToNewObject("Chilkat.BinData")

li_Success = loo_MimeData.LoadFile("qa_data/received.eml")
if li_Success = 0 then
    Write-Debug loo_MimeData.LastErrorText
    destroy loo_Dkim
    destroy loo_MimeData
    return
end if

//  A message may carry more than one DKIM signature.  Verify each in turn.  Signatures are
//  indexed in top-to-bottom header order.
li_NumSigs = loo_Dkim.NumDkimSigs(loo_MimeData)

for i = 0 to li_NumSigs - 1
    //  DkimVerify uses a cached public key when one matches the signature's selector and domain;
    //  otherwise it retrieves the key from DNS.
    li_Success = loo_Dkim.DkimVerify(i,loo_MimeData)
    if li_Success = 1 then
        Write-Debug "Signature " + string(i) + ": verified."
    else
        Write-Debug "Signature " + string(i) + ": verification failed."
    end if

    //  VerifyInfo contains JSON describing the most recent DkimVerify call (selector, domain,
    //  result, and so on).
    Write-Debug loo_Dkim.VerifyInfo
    //  JSON parsing code for this result can be generated at Chilkat's online tool:
    //  https://tools.chilkat.io/jsonParse
next


destroy loo_Dkim
destroy loo_MimeData