Tcl

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.

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Tcl


load ./chilkat.dll

set success 0

set mime [new_CkMime]

set success [CkMime_SetBodyFromPlainText $mime "This message will be signed."]
if {$success == 0} then {
    puts [CkMime_lastErrorText $mime]
    delete_CkMime $mime
    exit
}

#  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.
set pfxPassword "myPfxPassword"
set cert [new_CkCert]

set success [CkCert_LoadPfxFile $cert "qa_data/signer.pfx" $pfxPassword]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkMime $mime
    delete_CkCert $cert
    exit
}

#  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
#  original content and a separate signature part.
set success [CkMime_AddDetachedSignature $mime $cert]
if {$success == 0} then {
    puts [CkMime_lastErrorText $mime]
    delete_CkMime $mime
    delete_CkCert $cert
    exit
}

set success [CkMime_SaveMime $mime "qa_output/signed.eml"]
if {$success == 0} then {
    puts [CkMime_lastErrorText $mime]
    delete_CkMime $mime
    delete_CkCert $cert
    exit
}

puts "Detached signature added."

delete_CkMime $mime
delete_CkCert $cert