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

#include <C_CkDkim.h>
#include <C_CkByteData.h>

void ChilkatSample(void)
    {
    HCkDkim dkim;
    BOOL success;
    const char * password;
    HCkByteData mimeData;
    HCkByteData dkimSignedMime;

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

    dkim = CkDkim_Create();

    //  Any string automatically begins a fully-functional 30-day trial.

    success = CkDkim_UnlockComponent(dkim,"Anything for 30-day trial");
    if (success != TRUE) {
        printf("%s\n",CkDkim_lastErrorText(dkim));
        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..
    CkDkim_putDkimDomain(dkim,"chilkatsoft.com");
    CkDkim_putDkimSelector(dkim,"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.

    password = "optionalPassword";
    success = CkDkim_LoadDkimPkFile(dkim,"myPrivateKey.pem",password);
    if (success != TRUE) {
        printf("%s\n",CkDkim_lastErrorText(dkim));
        return;
    }

    //  Load a MIME file.
    mimeData = CkByteData_Create();

    success = CkByteData_loadFile(mimeData,"testMessage.eml");
    if (success != TRUE) {
        printf("Failed to load file.\n");
        return;
    }

    //  Sign it.  This adds the DKIM-Signature header and
    //  returns the new MIME with DKIM-Signature added.
    dkimSignedMime = CkByteData_Create();
    success = CkDkim_AddDkimSignature(dkim,mimeData,dkimSignedMime);
    if (success != TRUE) {
        printf("%s\n",CkDkim_lastErrorText(dkim));
        return;
    }

    success = CkByteData_saveFile(dkimSignedMime,"dkimSigned.eml");
    if (success != TRUE) {
        printf("Failed to save file.\n");
        return;
    }

    printf("Success.\n");

    CkDkim_Dispose(dkim);
    CkByteData_Dispose(mimeData);
    CkByteData_Dispose(dkimSignedMime);

    }