What determines whether encryption is used with the Signature SDK and can I turn it off?

The use of encryption by the Signature SDK depends on whether encryption is enabled on the signature pad.

With the STU pads you can run Identify.exe (one of our STU Utilities) to determine whether or not encryption is enabled. When the signature capture window appears a padlock icon indicates whether encryption is being used.

It is not possible to disable encryption programmatically on a pad which is already enabled for it.

DTUs use encryption all the time because that is what Wintab does - the Signature SDK has no control over this.