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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Java

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[])
  {
    boolean success = false;

    CkMime mime = new CkMime();
    success = mime.SetBodyFromPlainText("This message will be signed.");
    if (success == false) {
        System.out.println(mime.lastErrorText());
        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";
    CkCert cert = new CkCert();
    success = cert.LoadPfxFile("qa_data/signer.pfx",pfxPassword);
    if (success == false) {
        System.out.println(cert.lastErrorText());
        return;
        }

    //  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.
    success = mime.ConvertToSigned(cert);
    if (success == false) {
        System.out.println(mime.lastErrorText());
        return;
        }

    success = mime.SaveMime("qa_output/signed_opaque.eml");
    if (success == false) {
        System.out.println(mime.lastErrorText());
        return;
        }

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