(Java) 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.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkDkim dkim = new CkDkim();

    // 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.
    String password;
    password = "optionalPassword";
    CkPrivateKey privKey = new CkPrivateKey();
    boolean success = privKey.LoadAnyFormatFile("myPrivateKey.pem",password);
    if (success != true) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    success = dkim.SetDkimPrivateKey(privKey);
    if (success != true) {
        System.out.println(dkim.lastErrorText());
        return;
        }

    // Load a MIME file.
    CkByteData mimeData = new CkByteData();
    success = mimeData.loadFile("testMessage.eml");
    if (success != true) {
        System.out.println("Failed to load file.");
        return;
        }

    // Sign it.  This adds the DKIM-Signature header and
    // returns the new MIME with DKIM-Signature added.
    CkByteData dkimSignedMime = new CkByteData();
    success = dkim.AddDkimSignature(mimeData,dkimSignedMime);
    if (success != true) {
        System.out.println(dkim.lastErrorText());
        return;
        }

    success = dkimSignedMime.saveFile("dkimSigned.eml");
    if (success != true) {
        System.out.println("Failed to save file.");
        return;
        }

    System.out.println("Success.");
  }
}