You really only need authentication for that, not encryption. MACs and such are okay on ham bands as I understand it. You just can't obscure the message. If you want a private channel to the exclusion of other people, license a frequency and pay for it. Spectrum is a scarce resource.

You have to encrypt it.

NASA requires any of its propulsive spacecraft within 2 million kilometers of Earth to protect their command uplink with encryption that is compliant with Level 1 of the Federal Information Processing Standard (FIPS) 140-3 (10). The FCC has also considered requiring encryption on the telemetry, tracking, and command communications as well as mission data for propulsive spacecraft, but decided not to incorporate a specific requirement at this time. A satellite with an amateur license cannot encrypt transmissions in any way and must consist of open information. The eligibility rules are listed in 47 CFR Part 97.

https://www.law.cornell.edu/cfr/text/47/97.211