Add an S/MIME Detached Signature

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Demonstrates the Chilkat Mime.AddDetachedSignature method, which creates an S/MIME detached signature. The only argument is the signing Cert, which must have access to its private key. On success the entity becomes a multipart/signed with the content and a separate signature part.

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: A detached signature (multipart/signed) keeps the original content readable alongside a separate signature part — so recipients whose software does not understand S/MIME still see the message, they just cannot verify it. That backward compatibility makes detached the usual choice for signed email. The signer proves authorship with a certificate that carries its private key.

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bool success = false;

Chilkat.Mime mime = new Chilkat.Mime();
success = mime.SetBodyFromPlainText("This message will be signed.");
if (success == false) {
    Debug.WriteLine(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";
Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadPfxFile("qa_data/signer.pfx",pfxPassword);
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

//  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
//  original content and a separate signature part.
success = mime.AddDetachedSignature(cert);
if (success == false) {
    Debug.WriteLine(mime.LastErrorText);
    return;
}

success = mime.SaveMime("qa_output/signed.eml");
if (success == false) {
    Debug.WriteLine(mime.LastErrorText);
    return;
}

Debug.WriteLine("Detached signature added.");