“Packed shellcode is a common deterrent against reverse engineering. Mainstream software will use it in order to protect intellectual property or prevent software cracking. Malicious binaries and Capture the Flag (CTF) challenges employ packed shellcode to hide their intended functionality. However, creating these binaries is an involved process requiring significant experience with machine language. Due to the complexity of creating packed shellcode, the majority of samples are painstakingly custom-created or encoded with very simple mechanisms, such as a single byte XOR.
In order to aid in the creation of packed shellcode and better understand how to reverse engineer it, I created a tool to generate samples of modular packed shellcode. During this talk, I will demonstrate the use of the shellcode creation tool and how to reverse engineer the binaries it creates. I will also demonstrate an automated process for unpacking the binaries that are created.