Why would you want to transfer data between some two machines? You're inviting problems right there. You have to have a totally separate machine that: 1) you

Why would you want to transfer data between some two machines? You're inviting problems right there. You have to have a totally separate machine that: 1) you never ever connect to the internet, even for updates or installation of a cooler writing app 2) you never ever move data in or out - disable all data ports, especially USB and WiFi, at the very least in BIOS, preferably by physically disconnecting them inside. 3) you need to be able to inspect and modify that machine yourself (see pt 2), so pick something serviceable, like a ThinkPad (definitely not a Mac or anything unibody) 4) use an open-source operating system 5) obviously use full encryption - you'll get plenty of others' advice on that; use strong BIOS password both for boot and config 6) you probably don't want to spend a lot of money on a machine that's just a diary, so get a used ThinkPad. Depending on your preferred size, an X or T family. The _20 series is the last with a proper keyboard. So my suggestions would be X220, T420 or T520. (Or something older, if you don't care that much about performance, which is reasonable for what's essentially a typewriter. I guess you could get a working T400 (last of core2duos) for like $150.) 7) you make an exception for the "no data in or out" rule at the very beginning when you set up the OS and all needed apps - since there's no data (diary entries) to lose yet