I think about making something similar. Though the direction would be in reverse. Say a Pinephone with no way to ssh into by default that is normally powered o

I think about making something similar. Though the direction would be in reverse. Say a Pinephone with no way to ssh into by default that is normally powered off. No services listening on the network running on it + strict firewall. It can only initiate connections to other devices. Unless I want to sign a ssh key from a CA stored on it or provide a password to some of my other devices it's just powered off. All of DRAM is cleared prior to shutdown. Pinephone can boot to UI in ~2-3s so it would not be bothersome to keep it normally off, and boot up only when needed. Battery would last months for a single charge for this use case. It would run just a few processes. Init, maybe wpa_supplicant for wifi, and a UI process. Very simple SW, extremely limited attack surface. Pinephone has a nice feature that it can emulate any USB device, so I could connect it over USB to any machine, and just make it look like a keyboard, and just type in the username and password into a focused field, for the password filling feature. If I want to create a short term ssh certificate and sign a SSH key for access to a customer machine, the phone would connect to my workstation/notebook/whatever directly over ssh and sign/upload the certificate.