Here is the most comprehensicve page on ADSB that the FAA has.
Each committee has several working papers going. Intersting to note most of the versions now have a B or 2 designator, ie ADS-B2, Version 2 1090ES, Version 2 UAT, and MASPS was just re-written from 242A to 338
Transmitting and receiving subsystems compliant with DO-260B/ED-102A will use an ADS-B Version Number equal to two (2). In DO-260B/ED-102A the integrity level of the ADS-B source has been redefined and changes made to the definitions of the NIC and NAC parameters. Version 2 1090ES formats now include the transmission of selected altitude, selected heading, and barometric pressure setting in the target state and status messages. Version 2 1090ES formats also include the transmission of the Mode A (4096) code and the Register 3016 content of the TCAS/ACAS resolution advisory data.
and no where is there any encription.
RTCA SC-186 - Home Page – ADS-B Support