I struck a small blow for better security today.
It started last night on an IRC channel with A&D regular Susan Sons admonishing the regulars to rotate their ssh keys regularly – that is, generate and export new key pairs so that is someone cracks the crypto on one out of your sight it won’t be replayable forever.
This is one of those security tasks that doesn’t get done often enough because it’s a fiddly pain in the ass. But (I thought to myself) I have a tool that reduces the pain. Maybe I should try to eliminate it? And started hacking.
The tool was, until yesterday, named ssh-installkeys. It’s a script wrapper written in Python that uses a Python expect engine to login into remote sites and install (or remove) ssh public keys. What makes it useful is that it remembers a lot of annoying details like fixing file and directory permissions so your ssh server won’t see a potential vulnerability and complain. Also, unlike some competing tools, it only requires you to enter your password once per update.
Some time ago I taught this code to log its installations in a config file so you have a record of where you have remote-installed keys. I realized that with a little work this meant I could support a rotate option – mass-install new keys on every site you have recorded. And did that.
I’ve been meaning for some time to change the tool’s name; ssh-installkeys is too long and clumsy. So it’s now sshexport. I also updated it to know about, and generate, ed25519 keys (that being the new hotness in ssh crypto).
In order to reduce the pain, sshexport can now now store your passwords in its list of recorded sites, so you only have to enter the password the first time you install keys and all later rotations are no-hands operations. This doesn’t actually pose much additional security risk because by hypothesis anyone who can read this file has read access to your current private ssh keys already. The correct security measure is whatever you already do to protect other sensitive data in your dot directories, like GPG directories and web passwords stored by your browser. I use drive encryption.
The result is pretty good. Not perfect; the big missing feature is that it doesn’t know how to update your keys on sites like GitLab. That would take a custom method for each such site, probably implemented with curl. Perhaps in a future release.