(MFC) Verify DKIM-Signature Headers in Downloaded Email

Downloads email from an IMAP server and verifies the DKIM-Signature header(s) in each email, if present.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkImap.h>
#include <CkDkim.h>
#include <CkJsonObject.h>
#include <CkBinData.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkImap imap;

    // Connect to an IMAP server, login, select mailbox..
    // Use TLS 
    imap.put_Ssl(true);
    imap.put_Port(993);
    bool success = imap.Connect("imap.someMailServer.com");
    if (success == true) {
        success = imap.Login("myLogin","myPassword");
        if (success == true) {
            success = imap.SelectMailbox("Inbox");
        }

    }

    if (success != true) {
        strOut.append(imap.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkDkim dkim;

    // Download a max of 10 emails and verify any DKIM-Signature headers
    // that are present.

    // Download emails by sequence numbers (not UIDs).
    bool bUid = false;
    int seqNum;
    int j;
    int n = imap.get_NumMessages();
    if (n > 10) {
        n = 10;
    }

    CkJsonObject json;
    json.put_EmitCompact(false);

    // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
    CkBinData mimeData;
    seqNum = 1;
    while (seqNum <= n) {
        // The FetchSingleBd method was introduced in v9.5.0.76
        success = imap.FetchSingleBd(seqNum,bUid,mimeData);
        if (success != true) {
            strOut.append(imap.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        // Get the number of DKIM-Signature headers.
        int numDkim = dkim.NumDkimSigs(mimeData);

        // Verify each..
        j = 0;
        while (j < numDkim) {
            strOut.append("------ DKIM Signature ");
            strOut.appendInt(j);
            strOut.append("\r\n");

            success = dkim.DkimVerify(j,mimeData);
            if (success != true) {
                strOut.append("Not valid.");
                strOut.append("\r\n");
            }
            else {
                strOut.append("valid.");
                strOut.append("\r\n");
            }

            // Show the additional information about the signature verification
            json.Load(dkim.verifyInfo());
            strOut.append(json.emit());
            strOut.append("\r\n");

            // The JSON contains information such as this:

            // 	{
            // 	  "domain": "amazonses.com",
            // 	  "selector": "7v7vs6w47njt4pimodk5mmttbegzsi6n",
            // 	  "publicKey": "MIGfMA0GCSqG...v2GvWPqGHz6uqeQIDAQAB",
            // 	  "canonicalization": "relaxed/simple",
            // 	  "algorithm": "rsa-sha256",
            // 	  "signedHeaders": "Subject:From:To:Date:Mime-Version:Content-Type:References:Message-Id:Feedback-ID",
            // 	  "verified": "yes"
            // 	}

            j = j + 1;
        }

        seqNum = seqNum + 1;
    }

    success = imap.Disconnect();


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }