Tuesday, 22 November 2011

Javascript Obfuscation - Properties access

The way we access properties of an object in Javascript is pretty much straight forward with some tiny exceptions. What is interesting for obfuscation though is the way we use it and that's what we will see.

Common object properties access

The most common way to access property of an object is by using the dot notation. It's very simple, but for obfuscation it's not very convenient since we have to explicitly tell what property we want to access. However, there is a second way to access a property that is more convenient for obfuscation and it's with the bracket notation. Example :

var foo = {a : 1};
foo.a // dot notation
foo["a"] // bracket notation

The reason the second one is more convenient for obfuscation is that it takes a string and has we have seen before we can easily use obfuscation technique to produce the string we want. So the previous example can be rewritten has :

var foo = {a : 1};

Number properties access 

Numbers do have 2 extra ways to access their properties. Those 2 ways where made up because the dot notation is not adapted for numbers. For that reason we have the "dot-dot" notation and the "space-dot" notation to access properties of a number. They are usually unknown to most of the developer even from experienced Javascript developer. Example :

1..toFixed(2) === "1.00"
(1 .constructor+"")[11] === "m"

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