Notes on Reversing Java Applications

This tutorial aim is show some simple techniques that can be used to reverse and patching Java target, a first classical approach will be about the class decompilation with JAD and JODE decompiler, then we can move into the JVM (Java virtual machine) analysis and deeper into the bytecode analysis and patching.

In order to fix some concepts a simple Java CrackMe will be explored trough decompilation with the presented tool and bytecode patching by using IDA and Hex Editor. Of course this topic isn't new and was also covered into the past by other, but this essay will just point some well know concept and show some more hint about the Java patching, a minimum skill on the Java programming is needed to make code change and understand the program execution flow at the decompiled stage. Finally some consideration around how to better protect Java coded application was covered.