Lua

Add an S/MIME Detached Signature

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.

Chilkat Lua Downloads

Download Chilkat for Lua

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 S/MIME detached signature.  The object becomes a multipart/signed entity with the
-- original content and a separate signature part.
success = mime:add_detached_signature(cert)
if not success then
    print(mime.last_error_text)
    return
end

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

print("Detached signature added.")