level 1

Let's run the program.

sh-4.3$ ./level01
Enter the 3 digit passcode to enter:

As we can see we need to enter a 3 digit passcode.

We can disassemble the program using gdb to get an idea of how the program performs it's checks.

(gdb) disassemble main
Dump of assembler code for function main:
   0x08048080 <+0>:     push   $0x8049128
   0x08048085 <+5>:     call   0x804810f
   0x0804808a <+10>:    call   0x804809f
   0x0804808f <+15>:    cmp    $0x10f,%eax
   0x08048094 <+20>:    je     0x80480dc
   0x0804809a <+26>:    call   0x8048103
End of assembler dump.

We can see that the value stored in $eax is being compared to 0x10f. As this is the only comparison, this should be our input.

0x10f in decimal is 271. We can provide this value as the passcode and solve the level.