The current Act that is in force in Australia is found here:
https://www.legislation.gov.au/Details/C2018C00336
There are many regulations and licence conditions with various names that are derived or based on this act. You would need to review them all to see if any secrecy porvision applies to the license you are operationg under, such as an aeronautical license, the license conditions for this are found here:
https://www.legislation.gov.au/Details/F2015L00495 . No mention of secrecy in that.
In its assesment criteria the UoC AVIE4001 - Maintain aircraft radio communications does refer to:
- responsibilities of an aeronautical radio operator:
- secrecy of communications
- unauthorised transmissions
Though the actual compentancy document found here:
https://training.gov.au/Training/Details/AVIE4001 makes no mention of secrecy.
Must be a CASA thing I'd say......