SKILL.md
Reverse Engineering
Scope
Reverse engineering compiled binaries (ELF, PE, Mach-O) and bytecode artifacts to recover algorithms, validate inputs, or build static solvers. Focused on the recurring CTF / malware-analysis pattern of a host binary that loads a "program" file under a custom ISA — recognising the dispatcher loop, mapping opcodes to Python lambdas, and inverting the transformation chain in pure Python without executing the host. Also covers callfuscation (control-flow chunking), MBA (mixed boolean-arithmetic) operator obfuscation, encrypted-handler tricks, and three-layer deobfuscation pipelines.
When to use
- A binary plus a "program data" file are delivered together and the binary appears to be an interpreter (themed opcode names, dispatcher switch / jump table).
- Disassembly reveals a
while(true){ op = mem[pc++]; switch(op){...}; }style loop or jump-table indexed by opcode. - The binary is heavily obfuscated (callfuscation, MBA wrappers, encrypted handlers in
.datadecrypted to RWX at startup). - You need to recover an algorithm or check function from native code without dynamic execution (anti-debug, wrong arch, no TTY).
- Static-first reverse engineering is preferred (faster, more reliable than emulator chains).
References
- [reference/custom-vm-bytecode.md](reference/custom-vm-bytecode.md) — recognising and inverting custom stack/register/tape VMs; callfuscation linearization; MBA operator identification; encrypted-handler decryption.