IOLI Crackme 0x02

Writeup

In this write up i'll resolve the challenge IOLI Crackme specific the level 0x02 with the tool radare2. First of all run the executable to check a random password and validate. The hint in the repository tell about resolve the above operation of wich the result is 338724 if we check this password the crackme accept it.

((10*9)+(123*4))^2

After that lets analyzing with radare2. Like the previous writeup use aaaa to analyze the executable.

In the image below we can see a cmp to compare the variable and then a conditional jump jne (wich means jump if not equal). If the value is not equal jump to the print of "Invalid password" and if is equals print "Password OK" so this is our break point. To patch the binary we need to change the jne to NOP . The NOP is a instruction wich performs no operation, this instruction takes up space in the instruction stream. The opcode of NOP is 90 so we need to put that with the wx command and lenght of 9.

After that the binary accept any password.

;)

Binary source https://github.com/Maijin/radare2-workshop-2015/tree/master/IOLI-crackme

Reference https://c9x.me/x86/html/file_module_x86_id_217.html