Crackme writeup by @310hkc41b https://twitter.com/310hkc41b
You can download crackme0x08.exe from this link.
To solve this cackme we will only use static analysis.
We have the expected _main() function again in this crackme. So far nothing new.
In this case we can see that almost all the program logic (except for a couple of more functions) is in the _check() function.
The same checks are made. That the sum of the digits is 0x10 (16 decimal) and if this first condition is met, the _parell() function is called, which does the rest of the checks.
If the above is not true, the _che() function is called, which is the one that displays the message of "Incorrect Password" and exits the program.
Just below this function, all the code that is there is totally useless because it will not be executed under normal conditions, unless the user manipulates the code while analyzing it in the debugger.
Let's see what it does in the _parell() function ...
First it calls the _dummy() function that checks if there is an environment variable that starts with "LOL" and returns the result on a variable, and also sets a flag to 1 (for a double check).
If this environment variable exists, then it enters a loop that will do 10 times (in case the conditions are not met, something useless and absurd), and then it checks if the number is even and then it checks the LOL flag and displays the message of "Password OK".
And in the previous image you have the _dummy() function that checks the environment variables.
In fact this crackme does nothing different than the previous one in terms of checks, simply that the code is ordered differently to mislead the user, but the passwords that work are the same.
To put something different, i put the graph of calls between the different functions.
It's not pretty? :)
And here we check that the same passwords work.
