Tcl

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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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 OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
#  signed-data structure that wraps the content inside the signature.
set success [CkMime_ConvertToSigned $mime $cert]
if {$success == 0} then {
    puts [CkMime_lastErrorText $mime]
    delete_CkMime $mime
    delete_CkCert $cert
    exit
}

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

puts "Message converted to an opaque signed message."

delete_CkMime $mime
delete_CkCert $cert