I work on SE Linux to improve security for all computer users. I think that my work has gone reasonably well in that regard in terms of directly improving security of computers and helping developers find and fix certain types of security flaws in apps. But a large part of the security problems we have at the moment are related to subversion of Internet infrastructure. The Tor project is a significant step towards addressing such problems. So to achieve my goals in improving computer security I have to support the Tor project. So I decided to put my latest SE Linux Play Machine online as a Tor hidden service. There is no real need for it to be hidden (for the record it’s in my bedroom), but it’s a learning experience for me and for everyone who logs in.
A Play Machine is what I call a system with root as the guest account with only SE Linux to restrict access.
Running a Hidden Service
A Hidden Service in TOR is just a cryptographically protected address that forwards to a regular TCP port. It’s not difficult to setup and the Tor project has good documentation . For Debian the file to edit is /etc/tor/torrc.
I added the following 3 lines to my torrc to create a hidden service for SSH. I forwarded port 80 for test purposes because web browsers are easier to configure for SOCKS proxying than ssh.
HiddenServicePort 22 192.168.0.2:22
HiddenServicePort 80 192.168.0.2:22
Generally when setting up a hidden service you want to avoid using an IP address that gives anything away. So it’s a good idea to run a hidden service on a virtual machine that is well isolated from any public network. My Play machine is hidden in that manner not for secrecy but to prevent it being used for attacking other systems.
SSH over Tor
Howtoforge has a good article on setting up SSH with Tor . That has everything you need for setting up Tor for a regular ssh connection, but the tor-resolve program only works for connecting to services on the public Internet. By design the .onion addresses used by Hidden Services have no mapping to anything that reswemble IP addresses and tor-resolve breaks it. I believe that the fact that tor-resolve breaks thins in this situation is a bug, I have filed Debian bug report #776454 requesting that tor-resolve allow such things to just work .
ProxyCommand connect -5 -S localhost:9050 %h %p
I use the above ssh configuration (which can go in ~/.ssh/config or /etc/ssh/ssh_config) to tell the ssh client how to deal with .onion addresses. I also had to install the connect-proxy package which provides the connect program.
The authenticity of host ‘zp7zwyd5t3aju57m.onion (
ECDSA key fingerprint is 3c:17:2f:7b:e2:f6:c0:c2:66:f5:c9:ab:4e:02:45:74.
Are you sure you want to continue connecting (yes/no)?
I now get the above message when I connect, the ssh developers have dealt with connecting via a proxy that doesn’t have an IP address.