As as a seventh and last assignment of the 32-bit Securitytube Linux Assembly Expert, I have been tasked to create a custom shellcode crypter. The idea behind a crypter, is to encode the shellcode beforehand and decode it at runtime. This process will make the shellcode looks like random values, and thus aiming to bypass AV and IDS detection. When it comes to cryptography, it is a well-known wise approach to not try to reinvent the wheel and instead use what is available and well tested: this is done to prevent any new weakness or bug to be introduced in a a freshly written crypto-algorithm.

As a sixth assignment of the 32-bit Securitytube Linux Assembly Expert, I had to create three different polymorphic version of shellcodes taken from ShellStorm. Here is my selection: Linux x86 execve(“/bin/sh”) - 28 bytes. Linux x86 iptables flush - 43 bytes. Linux x86 ASLR deactivation - 83 bytes. Polymorphism means that we can mutate shellcode, so while keeping the same functionality the signature is different.