Recently I wrote a secret-sharing FUSE
secretfs. It is read-only and its purpose was purely to allow me to
recombine the secret shares which comprise my SSH and GPG private keys.
I now use this filesystem in conjunction with a simple shell script to start the FS when my desktop logs in, to provide me with my GPG and SSH keys whenever my USB key is present.
I created a 3-of-N share of my keys and then placed 2 on my USB key and 1 on each of my laptop, desktop and NAS.
If anyone wants more specific details of how it works, let me know. Otherwise enjoy. (P.S. I ended up removing my SSH key’s passphrase so that once the USB key is present, the ssh key “just works” without having to bother with the ssh agent. Simples)