Writing IA32 Restricted Instruction Set Shellcode Decoder Loops – This article addresses the requirements for writing a shellcode decoder loop using a limited number of characters that limits the instruction set. Most of it is based on the author’s experience with alphanumeric decoders but the principles apply to any piece of code that is written to work with a limited instruction set.
You can download it from the following link: https://packetstormsecurity.com/files/download/35079/whitepaper_shellcode.html
Source: https://packetstormsecurity.com/files/35079/whitepaper_shellcode.html.html