Easy Keyg3nme

Lets download the zip file and unzip it. (Password: crackmes.one)

Lets run the file

Its asks for a key, and it looks like if we type in the wrong key, its gives us a response saying nope.

Lets look at the file into more detail with the strings command

Ok so it looks like we will get a message saying Good job mate, now go keygen me if we give it the right key. Lets open the file with gdb and look at the functions

Lets look at the main function by disassembling it

We are calling the validate_key function, lets check it out

This line is the most interesting , we are using the imul instruction. Lets see what it does on google

So it multiplies the integers, so in the screenshot above, we are multiplying eax with itself, and the value being 0x4c7 which is also 1223 in decimal

So lets try entering 1223 as the key or any multiple of 1223 as the key as we are multiplying it by itself and storing it in a variable that is the valid key.

We have the answer