Rust

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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Rust


let mime = chilkat::Mime::new();
if mime.set_body_from_plain_text("This message will be signed.").is_err() {
    println!("{}", mime.last_error_text());
    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.
let pfx_password = "myPfxPassword".to_string();
let cert = chilkat::Cert::new();
if cert.load_pfx_file("qa_data/signer.pfx", &pfx_password).is_err() {
    println!("{}", cert.last_error_text());
    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.
if mime.convert_to_signed(&cert).is_err() {
    println!("{}", mime.last_error_text());
    return;
}

if mime.save_mime("qa_output/signed_opaque.eml").is_err() {
    println!("{}", mime.last_error_text());
    return;
}

println!("Message converted to an opaque signed message.");