Visual FoxPro

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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Visual FoxPro

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 S/MIME detached signature.  The object becomes a multipart/signed entity with the
*  original content and a separate signature part.
lnSuccess = loMime.AddDetachedSignature(loCert)
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
ENDIF

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

? "Detached signature added."

RELEASE loMime
RELEASE loCert