Hi, So many answers in this thread! I did not think this would generate so much interest. It looks like I am going to use a completely different method, but for the sake of interest in the answers, I am dropping here a more detailed description of what was initially intended.
What this does: The program runs with a dedicated user with limited rights. It pulls messages from an input queue system, encrypts them individually using symetric encryption and a passphrase, and then forwards them to another output queue system. There are several queues on the input system, each of these queues gets their individual passphrase, so I actually simplified when I was saying that I launch the program with exec prog # reads PASSPHRASE from the environment because what I actually do looks more like: exec chpst -u user env \ $(cat /etc/passphrases.env) \ program Where /etc/passphrases.env is only readable by root and looks like this: QUEUE1="mylongrandompassphrase1" QUEUE2="mylongrandompassphrase2" So the user running the program can read the passphrases from its environment, but cannot open the file /etc/passphrases.env. So runit is taking care of reading the file and "dropping privileges". Another thing I did not mention is that the input system has some limitations forcing me to create several instances of the daemon. As a consequence I have a master daemon that does: sv start daemon1 sv start daemon2 sv start daemon3 exec tailf /dev/null Now for extra security, we wanted to modify this so that the passphrases are not on disk. And yes, that means non interactive restart in case of a problem. This would protect us against physical theft of a hard drive. Funnily enought the plan was already to use pass (http://passwordstore.org) to store the passphrases, but one needs to unlock a gpg key in order to use it. So somehow the problem does not change and a passphrase needs to be entered when the daemon start. Ideally, the "master daemon" would ask for the passphrase of the gpg key, unlock it, use it get the relevant passphrases of the queues from the pass repository, and then start the slaves and somehow transmit these passphrases to each of them, and manage them from there. So here is the problem in full, which I break down to 2 tasks: - Get a passphrase at startup interactively from a master daemon (to unlock the gpg key and get the relevant passphrases from pass) - Transmit environment variables securely to several slaves But again, I am fairly certain we are going to use a whole different approach and just not encrypt these queues like this and rather do something on disk of the receiving system, so don't put too much thinking in there. Thank you so much for your insights! Cheers, Tof
