C

Verify DKIM-Signature Headers in Downloaded Email

See more DKIM / DomainKey Examples

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

#include <C_CkImap.h>
#include <C_CkDkim.h>
#include <C_CkJsonObject.h>
#include <C_CkBinData.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkImap imap;
    HCkDkim dkim;
    BOOL bUid;
    int seqNum;
    int j;
    int n;
    HCkJsonObject json;
    HCkBinData mimeData;
    int numDkim;

    success = FALSE;

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

    imap = CkImap_Create();

    // Connect to an IMAP server, login, select mailbox..
    // Use TLS 
    CkImap_putSsl(imap,TRUE);
    CkImap_putPort(imap,993);
    success = CkImap_Connect(imap,"imap.example.com");
    if (success == TRUE) {
        success = CkImap_Login(imap,"myLogin","myPassword");
        if (success == TRUE) {
            success = CkImap_SelectMailbox(imap,"Inbox");
        }

    }

    if (success != TRUE) {
        printf("%s\n",CkImap_lastErrorText(imap));
        CkImap_Dispose(imap);
        return;
    }

    dkim = CkDkim_Create();

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

    // Download emails by sequence numbers (not UIDs).
    bUid = FALSE;

    n = CkImap_getNumMessages(imap);
    if (n > 10) {
        n = 10;
    }

    json = CkJsonObject_Create();
    CkJsonObject_putEmitCompact(json,FALSE);

    // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
    mimeData = CkBinData_Create();
    seqNum = 1;
    while (seqNum <= n) {
        // The FetchSingleBd method was introduced in v9.5.0.76
        success = CkImap_FetchSingleBd(imap,seqNum,bUid,mimeData);
        if (success != TRUE) {
            printf("%s\n",CkImap_lastErrorText(imap));
            CkImap_Dispose(imap);
            CkDkim_Dispose(dkim);
            CkJsonObject_Dispose(json);
            CkBinData_Dispose(mimeData);
            return;
        }

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

        // Verify each..
        j = 0;
        while (j < numDkim) {
            printf("------ DKIM Signature %d\n",j);

            success = CkDkim_DkimVerify(dkim,j,mimeData);
            if (success != TRUE) {
                printf("Not valid.\n");
            }
            else {
                printf("valid.\n");
            }

            // Show the additional information about the signature verification
            CkJsonObject_Load(json,CkDkim_verifyInfo(dkim));
            printf("%s\n",CkJsonObject_emit(json));

            // 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 = CkImap_Disconnect(imap);


    CkImap_Dispose(imap);
    CkDkim_Dispose(dkim);
    CkJsonObject_Dispose(json);
    CkBinData_Dispose(mimeData);

    }