Lets see info about what is inside with general tools

    objdump --debugging ./mycrk
    readelf --debug-dump=line
    nm -a ./mycrk

Okey checked and havent found nothing interesting. There was hope to find some nice string that could look like key. ... but there was no candidates for such string. Only way now is too see disassembly if there is something interesting. Lets use objdump for that. Should be enought of objdump as its just 1 level.

    objdump -d ./mycrk

Okey we know that there is printed out first message and then we type in our key. First printf is for string and then scanf definetly to read our input.

    80483f1:       e8 ee fe ff ff          call   80482e4 <printf@plt>
    80483f6:       83 c4 10                add    $0x10,%esp
    80483f9:       83 ec 08                sub    $0x8,%esp
    80483fc:       8d 45 f4                lea    -0xc(%ebp),%eax
    80483ff:       50                      push   %eax
    8048400:       68 22 85 04 08          push   $0x8048522
    8048405:       e8 ba fe ff ff          call   80482c4 <scanf@plt>
    804840a:       83 c4 10                add    $0x10,%esp
    804840d:       8b 45 f8                mov    -0x8(%ebp),%eax
    8048410:       3b 45 f4                cmp    -0xc(%ebp),%eax
    8048413:       75 1d                   jne    8048432 <main+0x6e>

scanf has somekind of params at address 0x8048522. Lets check what it have ... and its "%d " ha then its scanf("%d ",(int)) then it reads integer we can assume that key are numbers only. In format string %d is signed number but who cares. And asume most easy task that it just compare with some number with are our searched key. Lets put breakpoint at 0x80483f6

    (gdb)break *0x80483f6

and step instruction by instruction. That %eax=%ebp-0x8 is decision to validate key and one of the values are our own second is 0x5b1270 lets do small translation and ...

int(0x5b1270) = 5968496

    ;at this point happends comparison for if input value is valid or not
    ; something like
    ; if scanf("%d",stdin) == cd_key
    804840d:    8b 45 f8                 mov    eax,DWORD PTR [ebp-0x8]
    8048410:    3b 45 f4                 cmp    eax,DWORD PTR [ebp-0xc]

And lets check our number ... and its correct

KEY: 5968496

Notes

break *0x000 breakpoint on address
x/i $pc print current position instruction
p $eflags print eflags
p $eax print register EAX values