Lua

Get the S/MIME Signer's Certificate

Demonstrates the Chilkat Mime.LastSignerCert method, which loads the signer certificate at a zero-based index from the most recent successful verification (or security-unwrapping) into a Cert. The first argument is the signer index and the second is the receiving Cert.

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: Verifying tells you the signature is mathematically valid, but you usually also need to know who signed — the subject, the issuer, the validity dates — to decide whether to trust it. This retrieves each signer's certificate after verification so your code can inspect and apply its own trust rules. A message can have multiple signers, so iterate from 0 to NumSignerCerts - 1.

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Lua

local chilkat = require("chilkat")

local mime = chilkat.Mime.new()
local success = mime:load_mime_file("qa_data/signed.eml")
if not success then
    print(mime.last_error_text)
    return
end

-- After a successful verification, load each signer's certificate to inspect it.  The 1st argument
-- is the zero-based signer index and the 2nd is a Cert object that receives the certificate.
success = mime:verify()
if not success then
    print(mime.last_error_text)
    return
end

local n = mime.num_signer_certs
local cert = chilkat.Cert.new()
for i = 0, n - 1 do
    success = mime:last_signer_cert(i, cert)
    if not success then
        print(mime.last_error_text)
        return
    end

    print("Signer " .. i .. ": " .. cert.subject_cn .. " (issued by " .. cert.issuer_cn .. ")")
end