2 rpis with key transfer and cyphertext transmitted over Rx/Tx. Air gapped is the only place you ever have plaintext. Cheap, small, and relatively easy to imple

2 rpis with key transfer and cyphertext transmitted over Rx/Tx. Air gapped is the only place you ever have plaintext. Cheap, small, and relatively easy to implement, but if a system like this fits somewhere in how you deal with your threat model, then your opsec is probably already compromised.