Lianja

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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llSuccess = .F.

loMime = createobject("CkMime")
llSuccess = loMime.SetBodyFromPlainText("This message will be signed.")
if (llSuccess = .F.) then
    ? loMime.LastErrorText
    release loMime
    return
endif

//  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.
lcPfxPassword = "myPfxPassword"
loCert = createobject("CkCert")
llSuccess = loCert.LoadPfxFile("qa_data/signer.pfx",lcPfxPassword)
if (llSuccess = .F.) then
    ? loCert.LastErrorText
    release loMime
    release loCert
    return
endif

//  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.
llSuccess = loMime.ConvertToSigned(loCert)
if (llSuccess = .F.) then
    ? loMime.LastErrorText
    release loMime
    release loCert
    return
endif

llSuccess = loMime.SaveMime("qa_output/signed_opaque.eml")
if (llSuccess = .F.) then
    ? loMime.LastErrorText
    release loMime
    release loCert
    return
endif

? "Message converted to an opaque signed message."


release loMime
release loCert