Many common and unusual algorithms, implemented in Python as learning exercises. If you want to get a sense of what, say, data structures or fuzzy logic would look like in Python, this is a good place to start.
A better, faster and stronger spiritual successor to BZip2. Features higher compression ratios and better performance thanks to a order-0 context mixing entropy coder, a fast Burrows-Wheeler transform code making use of suffix arrays and a RLE with Lempel Ziv+Prediction pass based on LZ77-style string matching and PPM-style context modeling.
Like its ancestor, BZip3 excels at compressing text or code.
In the AUR.
Self-made C++ file archiver and archive extractor programs based on Huffman's lossless compression algorithm.
CyberChef is a simple, intuitive web app for carrying out all manner of "cyber" operations within a web browser. These operations include simple encoding like XOR or Base64, more complex encryption like AES, DES and Blowfish, creating binary and hexdumps, compression and decompression of data, calculating hashes and checksums, IPv6 and X.509 parsing, changing character encodings, and much more.
The tool is designed to enable both technical and non-technical analysts to manipulate data in complex ways without having to deal with complex tools or algorithms. It was conceived, designed, built and incrementally improved by an analyst in their 10% innovation time over several years.
Online copy: https://gchq.github.io/CyberChef/
David MacKay has put the textbook he wrote online for everyone to download in a variety of formats. If you find it useful, consider buying a copy.
An open source utility that will crack the password used to encrypt .rar, .zip, and .7z archives. Runs multi-threaded to speed things up because it uses a brute-force attack.
Zopfli is a new data compression algorithm from researchers at Google which seems to work better than most existing compression algorithms out there. The trade off is that it can take much longer to finish compressing files, but more space and transmission time are saved. It is recommended for compress-once-distribute-many-times use cases.