Java

Create an Opaque (Attached) S/MIME Signature

Demonstrates the Chilkat Mime.ConvertToSigned method, which creates an opaque (attached) S/MIME signature. The only argument is the signing Cert. On success the entity is replaced by a CMS/PKCS #7 signed-data structure that wraps the content inside the signature.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: An opaque signature bundles the content inside the CMS structure, so the message is a single application/pkcs7-mime blob that only S/MIME-aware software can read. It is more tamper-resistant in transit — nothing can alter the content without breaking the wrapper — at the cost of the backward compatibility a detached signature offers. Use it when every recipient is known to support S/MIME.

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import com.chilkatsoft.chilkat2.Cert;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Mime;

public class ChilkatExample {

    public static void main(String[] args) {
        Mime mime = new Mime();
        try {
            mime.setBodyFromPlainText("This message will be signed.");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Load the signing certificate (which must have access to its private key) from a PFX file.
        // The PFX password should come from a secure source rather than being hard-coded.
        String pfxPassword = "myPfxPassword";
        Cert cert = new Cert();
        try {
            cert.loadPfxFile("qa_data/signer.pfx", pfxPassword);

            // Create an OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
            // signed-data structure that wraps the content inside the signature.
            mime.convertToSigned(cert);

            mime.saveMime("qa_output/signed_opaque.eml");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("Message converted to an opaque signed message.");
    }
}