Hello, The task was about finding the key that prints "You got it!" on the screen. This task can be solved by statically analyzing the binary. It requests 128 chars input from the stdin.
Then it reads 128 chars from its own memory space using them mmap() function. More details here http://man7.org/linux/man-pages/man2/mmap.2.html
Then it compares it to the entred key: it starts comparing the first char with 0x7f. ELF header ? (0x7F 'E' 'L' 'F')
Finally to get the validation key just type:
NcN_effaf80a641b28a8d8a750b99ef740593bb3dcbd
Cheers :-)
.text:08048525 mov eax, ds:stdin
.text:0804852A push eax
.text:0804852B push 80h
.text:08048530 push 1
.text:08048532 lea eax, [ebp-98h]
.text:08048538 push eax
.text:08048539 call _fread
.text:0804853E add esp, 10h
.text:08048541 cmp eax, 80h
Then it reads 128 chars from its own memory space using them mmap() function. More details here http://man7.org/linux/man-pages/man2/mmap.2.html
.text:08048578 sub esp, 8
.text:0804857B push 0
.text:0804857D push dword ptr [ebp-14h]
.text:08048580 push 2
.text:08048582 push 1
.text:08048584 push 80h
.text:08048589 push 0
.text:0804858B call _mmap
Then it compares it to the entred key: it starts comparing the first char with 0x7f. ELF header ? (0x7F 'E' 'L' 'F')
.text:080485DB cmp dword ptr [ebp-10h], 7Fh
head -c128 cannabinoid > ./cannabinoid
You got it!
Finally to get the validation key just type:
head -c128 cannabinoid | sha1sumNcN_effaf80a641b28a8d8a750b99ef740593bb3dcbd
Cheers :-)
