Chilkat2-Python

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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import sys
import chilkat2

success = False

mime = chilkat2.Mime()
success = mime.SetBodyFromPlainText("This message will be signed.")
if (success == False):
    print(mime.LastErrorText)
    sys.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.
pfxPassword = "myPfxPassword"
cert = chilkat2.Cert()
success = cert.LoadPfxFile("qa_data/signer.pfx",pfxPassword)
if (success == False):
    print(cert.LastErrorText)
    sys.exit()

# 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):
    print(mime.LastErrorText)
    sys.exit()

success = mime.SaveMime("qa_output/signed.eml")
if (success == False):
    print(mime.LastErrorText)
    sys.exit()

print("Detached signature added.")