Unless the root file system is encrypted this is a terrible idea. Everything that encryption protects you against would be negated. Somebody who gains remote access to your computer wouldn't need the keys since the disks would probably already be mounted. If, on the other hand, somebody gets local access (for example by stealing your disks) then the permissions on the file doesn't matter at all, the data is there on the disk and can be read by simply putting it in another computer. Don't store the keyfiles unencrypted unless the medium itself is reasonably safe (e.g. stored in a bank vault)