Tophography » Linux – Misc.

Netcat and OpenSSL’s s_client and s_server tools

Topher — Fri, 28 Sep 2007 20:58:02 +0000

Telnet is a wonderful tool for sysadmins and network application programmers. If you ever find yourself wearing either of these hats, you’ve got to know how to use telnet. Though, sometimes telnet requires a little too much from the user in order to get anything done. Netcat to the rescue! This is a tool that I’ve seen used before, but only recently really looked in to. Netcat (‘nc’) can be used as a server or a client, Netcat can be used to transmit files, Netcat can even be used as a port-scanner. Once I found myself trying to debug a web server with telnet. It was a pain to type in all the HTTP request headers by hand. If I would have known about Netcat, I could have just done this each time:
nc host 80 < request.txt
and just edited the request.txt file each time I wanted to try something different. Go read the man page (man nc), it’s actually well-written.

Now for the next cool tool! Ever wanted to do some testing on a server that uses TLS/SSL? Telnet obviously isn’t the answer. OpenSSL to the rescue!Â s_client lets you have the simple power of telnet, but it takes care of all the overhead of TLS/SSL.Â You can use s_client to test a server to find out if it will allow SSL2 sessions, or find out what happens if the client only requests certain ciphers.Â s_server gives you similar control from the server side.

Vim vs. Emacs : Resolved!

Topher — Fri, 07 Sep 2007 21:05:59 +0000

Here at UTOSC (the Utah Open Source Conference), I’ve found some very reliable evidence for which editor is better. After examining the sticker table, I found that the Vim stickers completely disappeared, while there are still a large number of Emacs stickers. I’m sure you all agree that this can finally end the debate.

Installing dsniff

Topher — Thu, 22 Feb 2007 00:09:34 +0000

I just thought Iâ€™d include a list of packages that I needed to install on my FC5 machine to get dsniff to compile.

db4-devel : Berkeley database libraries
libpcap : Libpcap
libnet : (API for network packet injection)
libnids : Network Intrusion Detection System (I got it from dries)
openssl-devel : OpenSSL libraries

After I installed these, the configure script completed, then I got some errors with make. I later realized that I ran into some major dependency-hell. Dsniff development stopped almost 6 years ago, and in that time, libnet and libnids have changed. I tried to find some older versions of the libraries, but no luck getting them old enough. I later found a couple rpms on the following site, but should I really trust them?

http://voidmain.is-a-geek.net/files/RPMS/dsniff/

[This post was rescued from Google Cache. Originally posted 10/11/06.]

Quick and Easy Histograms in gnuplot

Topher — Wed, 31 Jan 2007 23:51:51 +0000

I have to create histograms quite frequently for my Digital Signal Processing class this semester. Here’s a quick gnuplot setup for a histogram. You can either type these commands into gnuplot, or enter them into a file (usually with a .gpi extension), and use ‘gnuplot file.gpi’ or ‘load file.gpi’ inside gnuplot.

example:

set boxwidth VALUE # Probably 3-5. set xlabel "STRING" set ylabel "STRING" set term svg # Create an SVG image set output 'file.svg' set key off # Unless you really want a key # For this next line, lw is linewidth (2-4)? plot [XMIN:XMAX] 'myHistogramData' with boxes lw VALUE

The input is expected to be in this format:

x-value y-value x-value y-value etc...