Documentation
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Category: Linux
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Published: Thursday, 27 August 2015 22:25
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Written by Ben Tasker
Having kdump enabled on a server provides a number of benefits, not least that in the event of a kernel panic you can collect a core-dump to help investigations into the root cause. It may simply be bad luck, but my experience with Debian Jessie has been that JournalD is absolutely hopeless in the event of a kernel panic.
Pre SystemD we used to (sometimes) get a backtrace written out to a log, even a partial backtrace could help point investigations into a rough direction, but even with JournalD configured to pass through to rsyslogd those traces just don't seem to be appearing (which to be fair, might be because of the nature of the panic rather than the fault of journald).
This documentation details the steps required to install and configure KDump on Debian Jessie
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Category: Linux
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Published: Monday, 20 July 2015 03:50
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Written by Ben Tasker
You may not be finished
Although we've examined designing and implementing Tor Hidden Service in quite some depth, some users will likely find that there are still additional considerations that they need to make.
For example, whilst we discussed the risks of traffic leakage, we did very little to avoid it - one solution, assuming you have out-of-band access to the host system, is to add iptables rules to ensure that all TCP and DNS traffic is redirected to the ports operated by the Tor Daemon.
You'd still then need to look at filtering out other protocols (including UDP on all other ports) in case someone discovers a means to have your host system send arbitrary traffic.
Similarly, we haven't discussed the impact of your Guard being compromised, those with serious concerns may need to look at running their own guards to help reduce the effectiveness of common Hidden Service de-anonymisation attacks
It's also important to remember that this documentation may not cover threats which have not been discovered yet, security is a continuous exercise.
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Category: Linux
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Published: Monday, 20 July 2015 02:32
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Written by Ben Tasker
This is Part 3 of my Hidden Service From Scratch documentation. In Part One we designed and built our system, in Part Two we configured HTTP Hidden Service hosting.
In this documentation, we'll be looking more generally at user account and identity protection, as well as examining why you may need to maintain a certain level of paranoia even if your hidden service doesn't fall outside the law in your home country.
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Category: Linux
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Published: Monday, 20 July 2015 03:46
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Written by Ben Tasker
On a system with SELinux, upon attempting to start Tor, you may see errors similar to the following
[root@localhost tor]# service tor start
Raising maximum number of filedescriptors (ulimit -n) to 16384.
Starting tor: Apr 02 15:53:14.041 [notice] Tor v0.2.5.11 (git-83abe94c0ad5e92b) running on Linux with Libevent 1.4.13-stable, OpenSSL 1.0.1e-fips and Zlib 1.2.3.
Apr 02 15:53:14.042 [notice] Tor can't help you if you use it wrong! Learn how to be safe at https://www.torproject.org/download/download#warning
Apr 02 15:53:14.042 [notice] Read configuration file "/etc/tor/tor-rpm-defaults-torrc".
Apr 02 15:53:14.042 [notice] Read configuration file "/etc/tor/torrc".
Apr 02 15:53:14.056 [notice] Opening Socks listener on 127.0.0.1:8080
Apr 02 15:53:14.057 [warn] Could not bind to 127.0.0.1:8080: Permission denied
Apr 02 15:53:14.058 [notice] Opening DNS listener on 127.0.0.1:54
Apr 02 15:53:14.060 [warn] Could not bind to 127.0.0.1:54: Permission denied
Apr 02 15:53:14.060 [notice] Opening Transparent pf/netfilter listener on 127.0.0.1:9040
Apr 02 15:53:14.062 [warn] Could not bind to 127.0.0.1:9040: Permission denied
Apr 02 15:53:14.062 [warn] Failed to parse/validate config: Failed to bind one of the listener ports.
Apr 02 15:53:14.062 [err] Reading config failed--see warnings above.
/usr/bin/torctl start: tor could not be started
Which is almost certainly the result of a selinux policy
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Category: Linux
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Published: Monday, 20 July 2015 02:26
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Written by Ben Tasker
Despite some fairly negative media attention, not every Tor Hidden Service is (or needs to be) a hotbed of immorality. Some exist in order to allow those in restrictive countries to access things we might take for granted (like Christian materials).
Whilst I can't condone immoral activities, Tor is a tool, and any tool can be used or misused
This is part Two in a detailed walk through of the considerations and design steps that may need to be made when setting up a new Tor Hidden Service.
The steps provided are intended to take security/privacy seriously, but won't defend against a wealthy state-backed attacker.
In Part One we looked at the system design decisions that should be made, and configured a vanilla install ready for hosting hidden services.
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