B4X

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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B4X

Dim success As Boolean = False

Dim mime As ChilkatMime
mime.Initialize
success = mime.SetBodyFromPlainText("This message will be signed.")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If

'  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.
Dim pfxPassword As String = "myPfxPassword"
Dim cert As ChilkatCert
cert.Initialize("cert")
success = cert.LoadPfxFile("qa_data/signer.pfx", pfxPassword)
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


'  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
'  original content and a separate signature part.
success = mime.AddDetachedSignature(cert)
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


success = mime.SaveMime("qa_output/signed.eml")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If

Log("Detached signature added.")