Cryptography & Theory 1: Meaning of Secure

Cryptography & Theory is series of blog posts on things I learned in coursera stanford online crypto class. The class contained just right mixture of theory, math and programming and I enjoyed it a lot.

This first part explains what is meant by expression "good cipher". It contains definition of a cipher and multiple definitions of cipher security. Although it does not sounds like much, it is one of the most important things I learned there.

It is important because ciphers are designed to protect against well defined attacks and are vulnerable to anything else. One can not just take random cipher from build-in ciphers list of his favorite framework and call it a day. One has to understand what is he choosing and why.

Matasano Crypto Challenge

I recently finished Matasano Crypto Challenges and it was an interesting experience. I started doing them because @tqbf tweets with standings showed up in my tweet feed and made me feel competitive. Now I'm very glad I did them.

Update: competition is not running anymore. All exercises and official solutions are available on cryptopals.org. My solutions are written in java and stored in matasano-cryptopals-solutions github repository.

Crypto Challenges is a collection of 48 exercises that demonstrate attacks on real world ciphers and protocols. Exercises exploit both badly designed systems and subtle implementation bugs in theoretically rock solid crypto. Most importantly, they make you see how tricky the security can be and how much various details matter.

If you solved all exercises while the competition was running, Matasano donated 20$ to a charity.

Building JavaScript Library with Grunt.js

New release of typical non trivial JavaScript project needs to run unit tests, concatenate all source files into one and minify the result. Some of them also use code generators, coding style validators or other build time tools.

Grunt.js is an open source tool able to perform all above steps. It is pluginable and was written in JavaScript, so anyone working on JavaScript library or project should be able to extend it as he needs.

Less CSS - Expressions and Traps

In an average case, less expressions are easy to use, very useful and behave the same way as expressions in any other programming language. Unfortunately, their interactions with the rest of css syntax can occasionally cause somewhat quirky behavior. Adding to that, next less language version will change in backward incompatible way and expressions are affected too.

This post shows when and why quirky behavior happens, which problems are going to be solved by planned changes and which traps will still remain there.

Less CSS - Tips and Trics

Less is declarative language designed to behave and look as closely to css as possible. Less started as an attempt to make css style sheets easier to read and maintain and then added more features and abilities. It evolved so much that it became theoretically possible to do anything with it.

This post shows some less known but very useful less features. It also contains list of potentially useful workarounds and tricks you can use if the default less syntax is not sufficient for what you need. Finally, last chapter shows one practical application of those tricks. We will create mixin to auto generate vendor prefixes for css declarations.

ANTLR - Semantic Predicates

Parsing simple grammar with antlr is simple. All you have to do is to use regular expressions to describe your language and let antlr generate lexer and parser. Parsing big or complicated languages occasionally require more, because describing them in regular expressions only can be hard or even impossible.

Semantic predicates are java (or C++, or JavaScript, or ...) conditions written inside the grammar. Antlr uses them either to choose between multiple alternatives or as additional assertions to be checked. They can be placed inside both lexer and parser, but this post focus only on their usage within the parser. They add a lot of power to antlr.

Project Report - Less4j

Few months ago I decided to create java port of less.js. Less is an extension of CSS - it adds constants, mixins, ruleset nesting, namespaces and so on. Both reasons why I picked up less and short less introduction are written in introduction into less.

This report starts with current project status and its possible future directions. Second part recaps development and my experiences with used tools. Finally, the last part sums up why did I started with the project in the first place and whether it was worth it.