This is because the thumb drive is a vfat device, which has a very limited permissions model. The permissions of every file, as reported by the device driver, are always 0644, and there is no escape. When I try to add the identity from the key file, ssh-add says:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: UNPROTECTED PRIVATE KEY FILE! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ Permissions 0644 for '/media/USB20FD/.ssh/id_dsa' are too open. It is required that your private key files are NOT accessible by others. This private key will be ignored. Which is not really correct for this case. To read the file, you still have to possess the actual thumb drive. This is more secure than a file on a shared or networked system with mode 0600. I could work around this by copying the key file from the thumb drive to the local computer, which defeats the whole purpose. Short of rewriting the device driver, what can I do? My system is: Linux ortolan 3.2.0-57-generic #87-Ubuntu SMP Tue Nov 12 21:35:10 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
