Tor-ramdisk is a uClibc-based micro Linux distribution whose sole purpose is to securely host a Tor server purely in RAM. For those not familiar with Tor, it is a system which allows the user to construct encrypted virtual tunnels which are randomly relayed between Tor servers (nodes) until the connection finally exits to its destination on the internet. The encryption and random relaying resist traffic analysis in that a malicious sniffer cannot easily discover where the traffic is coming from or what data it contains. While not perfect in its efforts to provide users with anonymity, Tor does help protect against unscrupulous companies, individuals or agencies from "watching us". For more information, see the Tor official site.
The usefulness of a RAM only environment for Tor became apparent to me when Janssen was arrested by the German police towards the end of July, 2007. (You can read the full story in a CNET article.) While the police did not seize the computer for whatever reasons, they certainly could have. More typically, it would have been taken for forensic analysis of the data on the drives. Of course, if the computer housing the Tor server has no drives, there can be no question that it is purely a network relaying device and that one should look elsewhere for the "goods".
Other advantages became clear:
- It is useful to operators that want all traces of the server to disappear on powerdown. This includes the private SSL keys which can be housed externally.
- The environment can be hardened in a manner specific to the limited needs of Tor.
- It has the usual speed advantages of diskless systems and can run on older hardware.
The only known disadvantage is that it cannot host Tor hidden services which would require other services (e.g. http), and their resources (e.g. hard drive space), in addition to the Tor server itself. However, as a middle or exit node, it is ideal.