There are cryptographic primitives that can be instantiated via a multiparty key signing ceremony when the satellites are commissioned and then the keys thrown

There are cryptographic primitives that can be instantiated via a multiparty key signing ceremony when the satellites are commissioned and then the keys thrown away. After that, you'd have to grab a satellite and disassemble it in a clean room and use some kind of nanometer-scale logic probe to extract secret key information to Sybil attack anything.