Visual FoxPro

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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LOCAL lnSuccess
LOCAL loMime
LOCAL lcPfxPassword
LOCAL loCert

lnSuccess = 0

loMime = CreateObject('Chilkat.Mime')
lnSuccess = loMime.SetBodyFromPlainText("This message will be signed.")
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    CANCEL
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('Chilkat.Cert')
lnSuccess = loCert.LoadPfxFile("qa_data/signer.pfx",lcPfxPassword)
IF (lnSuccess = 0) THEN
    ? loCert.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
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.
lnSuccess = loMime.ConvertToSigned(loCert)
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
ENDIF

lnSuccess = loMime.SaveMime("qa_output/signed_opaque.eml")
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
ENDIF

? "Message converted to an opaque signed message."

RELEASE loMime
RELEASE loCert