SD cards have SPI pins, so I recommend SD for Trusted Stick rather than repurposed USB. I've bought a 512GB SDXC card for the purpose of backing up my laptop,

SD cards have SPI pins, so I recommend SD for Trusted Stick rather than repurposed USB. I've bought a 512GB SDXC card for the purpose of backing up my laptop, and often wonder whether to use it as a boot device. It's much less vulnerable to theft when it's safe in my pockets, compared to in a bag. I'd make one small change. Rather than aim for a laptop first, mod a WiFi SD card or other pocket-sized device. The KeyAsic platform (PQI Air Card/Transcend) has been extensively hacked, and Ubuntu can run on it. Client devices (laptop, phone, etc) could connect over WiFi and run VNC through a web browser. It's still vulnerable to keystroke logging on the client, but it would be possible to switch clients halfway through typing important messages. In my opinion the most secure client device would be an iPod running Rockbox, and connecting to the PQI Air Card over serial. My "WiPod" seems like the closest thing we have to a practical pocket-sized open source device, and it lets me share photos from an SD card to my phone :).