Add DKIM-Signature Header to MIME / Email

Demonstrates how to add a DKIM-Signature header field to a MIME message.

Note: The DKIM / DomainKey functionality is included with the Chilkat MIME license.

Downloads:

MS Windows Visual C/C++ Libraries

Linux/CentOS C/C++ Libraries

MAC OS X C/C++ Libraries

Solaris C/C++ Libraries

C++ Builder Libraries

// Needs #include <CkDkim.h>
// Needs #include <CkByteData.h>

    CkString strOut;

    //  Important: It is helpful to send the contents of the
    //  dkim.LastErrorText property when requesting support.

    CkDkim dkim;

    //  Any string automatically begins a fully-functional 30-day trial.
    bool success;
    success = dkim.UnlockComponent("Anything for 30-day trial");
    if (success != true) {
        strOut.append(dkim.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    //  To create a DKIM signature for email (i.e. MIME),
    //  you'll need to provide the following:
    //  (1) An RSA private key in any common file format.
    //  (2) The domain name (typically the same domain
    //  as the sender of an email).
    //  (3) A selector for the domain name -- an arbitrary string
    //  to identify the matching public key in DNS.

    //  To allow an email recipient to verify the DKIM signature via an
    //  external email client supporting DKIM or using other software,
    //  you will need to create a DNS record with the selector
    //  and matching public key.  This example does not provide
    //  information about DKIM DNS record creation.
    //  (Chilkat does not provide an API for creating DNS records.
    //  Creating the DKIM DNS record is something you would do
    //  manually.)

    //  Set the domain and selector:
    //  You'll need to provide your own values here..
    dkim.put_DkimDomain("chilkatsoft.com");
    dkim.put_DkimSelector("tuna");

    //  Load a private key from any common RSA private key
    //  format, such as DER, PKCS8, PEM, XML, etc.
    //  The LoadDkimPkFile method automatically detects
    //  the file format and reads it appropriately.
    //  If a password is not required, you'll still need to provide
    //  a password string argument, but it is ignored.
    const char * password;
    password = "optionalPassword";
    success = dkim.LoadDkimPkFile("myPrivateKey.pem",password);
    if (success != true) {
        strOut.append(dkim.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    //  Load a MIME file.
    CkByteData mimeData;

    success = mimeData.loadFile("testMessage.eml");
    if (success != true) {
        strOut.append("Failed to load file.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    //  Sign it.  This adds the DKIM-Signature header and
    //  returns the new MIME with DKIM-Signature added.
    CkByteData dkimSignedMime;
    success = dkim.AddDkimSignature(mimeData,dkimSignedMime);
    if (success != true) {
        strOut.append(dkim.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    success = dkimSignedMime.saveFile("dkimSigned.eml");
    if (success != true) {
        strOut.append("Failed to save file.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    strOut.append("Success.\r\n");

    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());