Lua

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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Lua

local chilkat = require("chilkat")

local mime = chilkat.Mime.new()
local success = mime:set_body_from_plain_text("This message will be signed.")
if not success then
    print(mime.last_error_text)
    return
end

-- 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.
local pfxPassword = "myPfxPassword"
local cert = chilkat.Cert.new()
success = cert:load_pfx_file("qa_data/signer.pfx", pfxPassword)
if not success then
    print(cert.last_error_text)
    return
end

-- 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:convert_to_signed(cert)
if not success then
    print(mime.last_error_text)
    return
end

success = mime:save_mime("qa_output/signed_opaque.eml")
if not success then
    print(mime.last_error_text)
    return
end

print("Message converted to an opaque signed message.")