This paper describes an attempt to write Win32 shellcode that is as small as possible, to perform a common task subject to reasonable constraints. The solution presented implements a bindshell in 191 bytes of null-free code, and outlines some general ideas for writing small shellcode.
You can download it from the following link: https://packetstormsecurity.com/files/download/40192/WritingSmallShellcode.pdf
Source: https://packetstormsecurity.com/files/40192/WritingSmallShellcode.pdf.html