In cryptography work, RC4 (Rivest Cipher 4) is well known as both one of the easiest to implement and fastest to run symmetric encryption algorithms. Unfortunately, over time there have been a number of attacks on RC4, both in poorly written protocols (such as in the case of WEP) or statistical attacks against the protocol itself.
Still, for how well it formed, it’s an amazingly simple algorithm, so I decided to try my hand at implementing it.
I had an interesting problem recently on a project I was working on. It’s a simple Flask-based webapp, designed to be deployed to AWS using Docker. The application worked just fine when I was running it locally, but as soon as I pushed the docker container…
Latency spikes. Bad enough that the application was failing AWS’s healthy host checks, cycling in and out of existence1:
Loving data as much as I do, I like to optimize things. To make sure I’m actually going the right way, it’s useful to time things. While it’s trivial in most languages to add timing, it’s even easier if you don’t have to.
After all of these updates to my dotfiles, I finally want something that I can use to keep them up to date. For that, let’s write a quick script that can do just that.
Sometimes cat just prints too quickly.
Another random task that I find myself doing distressingly often: performing a regular expression search and replace recursively across a bunch of files. You can do this relatively directly with tools like sed, but I can never quite remember the particularly flavor of regular expression syntax sed uses.
It’s been a while, so I figured I should get in a quick coding post. From /r/dailyprogrammer, we have this challenge:
The Gorellians, at the far end of our galaxy, have discovered various samples of English text from our electronic transmissions, but they did not find the order of our alphabet. Being a very organized and orderly species, they want to have a way of ordering words, even in the strange symbols of English. Hence they must determine their own order.
For instance, if they agree on the alphabetical order: UVWXYZNOPQRSTHIJKLMABCDEFG
Then the following words would be in sorted order based on the above alphabet order: WHATEVER ZONE HOW HOWEVER HILL ANY ANTLER COW
Quite often when working with internet data, you will find yourself wanting to figure out what sort of device users are using to access your content. Luckily, if you’re using HTTP, there is a standard for that: The user-agent header.
Since I’m in exactly that position, I’ve added a new script to my Dotfiles that reads user agents on stdin, parses them, and writes them back out in a given format.
A fairly common set of command line tools (at least for me) is to combine sort and uniq to get a count of unique items in a list of unsorted data. Something like this:
$ find . -type 'f' | rev | cut -d "." -f "1" | rev | sort | uniq -c | sort -nr | head
2649 htm
1458 png
993 cache
612 jpg
135 css
102 zip
99 svg
60 gif
45 js
27 pdf
For a research project I’m working on, it has become necessary to scan potentially large IPv4 prefixes in order to find any DNS revolvers that I can and classify them as either open (accepting queries from anyone) or closed.
Disclaimer: This is a form of port scanning and thus has associated ethical and legal considerations. Use it at your own risk.
This project is available on GitHub: jpverkamp/dnsscan