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IOLI 0x01

This is the second IOLI crackme.

$ ./crackme0x01
IOLI Crackme Level 0x01
Password: test
Invalid Password!

Let's check for strings with rabin2.

$ rabin2 -z ./crackme0x01
vaddr=0x08048528 paddr=0x00000528 ordinal=000 sz=25 len=24 section=.rodata type=a string=IOLI Crackme Level 0x01\n
vaddr=0x08048541 paddr=0x00000541 ordinal=001 sz=11 len=10 section=.rodata type=a string=Password:
vaddr=0x0804854f paddr=0x0000054f ordinal=002 sz=19 len=18 section=.rodata type=a string=Invalid Password!\n
vaddr=0x08048562 paddr=0x00000562 ordinal=003 sz=16 len=15 section=.rodata type=a string=Password OK :)\n

This isn't going to be as easy as 0x00. Let's try disassembly with r2.

$ r2 ./crackme0x01 -- Use `zoom.byte=printable` in zoom mode ('z' in Visual mode) to find strings
[0x08048330]> aa
[0x08048330]> pdf@main
/ (fcn) main 113
|          ; var int local_4 @ ebp-0x4
|          ; DATA XREF from 0x08048347 (entry0)
|          0x080483e4    55           push ebp
|          0x080483e5    89e5         mov ebp, esp
|          0x080483e7    83ec18       sub esp, 0x18
|          0x080483ea    83e4f0       and esp, -0x10
|          0x080483ed    b800000000   mov eax, 0
|          0x080483f2    83c00f       add eax, 0xf
|          0x080483f5    83c00f       add eax, 0xf
|          0x080483f8    c1e804       shr eax, 4
|          0x080483fb    c1e004       shl eax, 4
|          0x080483fe    29c4         sub esp, eax
|          0x08048400    c7042428850. mov dword [esp], str.IOLI_Crackme_Level_0x01_n ; [0x8048528:4]=0x494c4f49  ; "IOLI Crackme Level 0x01." @ 0x8048528
|          0x08048407    e810ffffff   call sym.imp.printf
|             sym.imp.printf(unk)
|          0x0804840c    c7042441850. mov dword [esp], str.Password_ ; [0x8048541:4]=0x73736150  ; "Password: " @ 0x8048541
|          0x08048413    e804ffffff   call sym.imp.printf
|             sym.imp.printf()
|          0x08048418    8d45fc       lea eax, dword [ebp + 0xfffffffc]
|          0x0804841b    89442404     mov dword [esp + 4], eax ; [0x4:4]=0x10101
|          0x0804841f    c704244c850. mov dword [esp], 0x804854c ; [0x804854c:4]=0x49006425  ; "%d" @ 0x804854c
|          0x08048426    e8e1feffff   call sym.imp.scanf
|             sym.imp.scanf()
|          0x0804842b    817dfc9a140. cmp dword [ebp + 0xfffffffc], 0x149a
|      ,=< 0x08048432    740e         je 0x8048442
|      |   0x08048434    c704244f850. mov dword [esp], str.Invalid_Password__n ; [0x804854f:4]=0x61766e49  ; "Invalid Password!." @ 0x804854f
|      |   0x0804843b    e8dcfeffff   call sym.imp.printf
|      |      sym.imp.printf()
|     ,==< 0x08048440    eb0c         jmp 0x804844e ; (main)
|     ||   ; JMP XREF from 0x08048432 (main)
|     |`-> 0x08048442    c7042462850. mov dword [esp], str.Password_OK____n ; [0x8048562:4]=0x73736150  ; "Password OK :)." @ 0x8048562
|     |    0x08048449    e8cefeffff   call sym.imp.printf
|     |       sym.imp.printf()
|     |    ; JMP XREF from 0x08048440 (main)
|     `--> 0x0804844e    b800000000   mov eax, 0
|          0x08048453    c9           leave
\          0x08048454    c3           ret

"aa" tells r2 to analyze the whole binary, which gets you symbol names, among things.

"pdf" stands for

  • Print

  • Disassemble

  • Function

This will print the disassembly of the main function, or the main() that everyone knows. You can see several things as well: weird names, arrows, etc.

  • "imp." stands for imports. Those are imported symbols, like printf()

  • "str." stands for strings. Those are strings (obviously).

If you look carefully, you'll see a cmp instruction, with a constant, 0x149a. cmp is an x86 compare instruction, and the 0x in front of it specifies it is in base 16, or hex (hexadecimal).

0x0804842b    817dfc9a140. cmp dword [ebp + 0xfffffffc], 0x149a

You can use radare2's ? command to get it in another numeric base.

[0x08048330]> ? 0x149a
5274 0x149a 012232 5.2K 0000:049a 5274 10011010 5274.0 0.000000

So now we know that 0x149a is 5274 in decimal. Let's try this as a password.

$ ./crackme0x01
IOLI Crackme Level 0x01
Password: 5274
Password OK :)

Bingo, the password was 5274. In this case, the password function at 0x0804842b was comparing the input against the value, 0x149a in hex. Since user input is usually decimal, it was a safe bet that the input was intended to be in decimal, or 5274. Now, since we're hackers, and curiosity drives us, let's see what happens when we input in hex.

$ ./crackme0x01
IOLI Crackme Level 0x01
Password: 0x149a
Invalid Password!

It was worth a shot, but it doesn't work. That's because scanf() will take the 0 in 0x149a to be a zero, rather than accepting the input as actually being the hex value.

And this concludes IOLI 0x01.