click, and go to page 39 No. They do not perform scrambling/descrambling.
In 1A2 systems, on standard 400-type line cards, STA T&R (and the internal circuitry of the telset, such as the network, transmitter and receiver) can be accessed at the CO T&R terminals of the card, if a phone is on-hook, and a line key is depressed.
When a line is idle, or placed on Hold, (and the user has an expectation of privacy) a listening device could be attached to the CO T&R, allowing eavesdropping of the office to occur via the STA T&R leads.
These cards, like the SanBar 4001A & B versions and several others, have a wiring option / feature that prevents the CO T&R from reaching the telephone set when the line is idle or on Hold, preventing electronic eavesdropping.
Interestingly, the SanBar company made them, and then they went out of business. The name "Exbar" suggests that former employees may have taken the design and formed a new company to supply these cards to the TSG. (Just a wild guess, of course, but if I had done that, I probably would have used that name, too.)