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[crackme] My take on a crackme
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nog_lorp
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PostPosted: Sun Mar 04, 2007 10:51 pm    Post subject: [crackme] My take on a crackme Reply with quote

Tell me what you think, and how hard you find it. If you get it right it will bell (the "wrong" message looks a little similar to the "right" message if you are just glancing).

The goal is to guess the number, which is input as an argument. The goal is not to get it to display the "correct" messag by patching it, thats easy as hell.

It is not packed and doesn't use any encryption.

Enjoy!
~nog_lorp

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nog_lorp
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PostPosted: Sun Mar 04, 2007 10:55 pm    Post subject: Reply with quote

Crashes with no argument silly. I should have fixed that but I was lazy.

cracknog.exe guessnumber

And... damn x0r do you ever leave this forum? Don't you eat and stuff like that? Very Happy

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nog_lorp
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PostPosted: Sun Mar 04, 2007 11:15 pm    Post subject: Reply with quote

Err... patching? The goal is to find the correct input, not patch it.
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Ungreat
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PostPosted: Sun Mar 04, 2007 11:29 pm    Post subject: Reply with quote

This is my idea of a good time.

*censored user*: I think you just can't figure it out Razz This algorithm looks liek a dummy to me Confused Analyzing further though.

Nice job with this

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Code:
mov     r10, qword ptr [rsp+0A28h+arg_5F8]
shl     rdx, 20h
mov     r11, 7010008004002001h
or      rax, rdx
mov     rcx, r10
xor     rcx, rax
lea     rax, [rsp+0A28h+var_2C8]
Oh man, I'm getting too excited


Last edited by Ungreat on Sun Mar 04, 2007 11:38 pm; edited 1 time in total
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nog_lorp
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PostPosted: Sun Mar 04, 2007 11:31 pm    Post subject: Reply with quote

Well, a little addition and subtraction, and lotsa bitwise operations Very Happy. There are some fun tricks in there too. Try breaking somewhere in that algorithm and then restarting it Very Happy.

~nog_lorp

EDIT: hehe, x0r = Irwin?

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Last edited by nog_lorp on Sun Mar 04, 2007 11:33 pm; edited 1 time in total
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nog_lorp
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PostPosted: Sun Mar 04, 2007 11:34 pm    Post subject: Reply with quote

Nope. Try it Very Happy. Although now that I think of it, I should have used the anti-break trick on that part too, just for added confusion.

~nog_lorp

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john0312
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PostPosted: Sun Mar 04, 2007 11:35 pm    Post subject: Reply with quote

nog_lorp wrote:
Well, a little addition and subtraction, and lotsa bitwise operations Very Happy. There are some fun tricks in there too. Try breaking somewhere in that algorithm and then restarting it Very Happy.

~nog_lorp

EDIT: hehe, x0r = Irwin?


x0r == Irwin == Killuminati....

Don't put up this kind of easy stuff, give him some VM to taste!

Well, I fail English, x0r fail math! LoLx!

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SMN
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PostPosted: Sun Mar 04, 2007 11:38 pm    Post subject: Reply with quote

Code:
00401660     74 0E          JNZ SHORT cracknog.00401670


Changed to JE and after running again, made my system beep 3 times. >Sad
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nog_lorp
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PostPosted: Sun Mar 04, 2007 11:39 pm    Post subject: Reply with quote

x0r: No, its not correct at all, sorry Sad
The solution will never be present in the program memory unless you enter it.

~nog_lorp
Edit: guy with monkey ass avitar: good, now trace back and find the right number to enter.

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Last edited by nog_lorp on Sun Mar 04, 2007 11:40 pm; edited 1 time in total
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john0312
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PostPosted: Sun Mar 04, 2007 11:39 pm    Post subject: Reply with quote

x0r wrote:
John, I glanced over it for a few seconds, so yes: My math in dire need of help,

I will try to do my best to help your math, since you "helped" me so much by using vocabs that I do not understand, thus adding entry to my vocab book!

x0r wrote:
idiot.

Yes, it is a nice way to address people like that. Razz

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john0312
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PostPosted: Sun Mar 04, 2007 11:43 pm    Post subject: Reply with quote

x0r wrote:
how gracious of you Smile

Yes, thank you for your compliment.

x0r wrote:
Would you rather me refer to you as a bastard or will your father sue me?


You see, my dad's a kind man, and I appreciate you for addressing me as a bastard.

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nog_lorp
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PostPosted: Sun Mar 04, 2007 11:47 pm    Post subject: Reply with quote

Wow, talk about love-hate! Got anything to say about the thread though? Very Happy

~nog_lorp

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john0312
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PostPosted: Sun Mar 04, 2007 11:50 pm    Post subject: Reply with quote

nog_lorp wrote:
Wow, talk about love-hate! Got anything to say about the thread though? Very Happy

~nog_lorp


Not bad, but:
- Too mathematically-focused
- Still spaces for improvement.

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john0312
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PostPosted: Sun Mar 04, 2007 11:55 pm    Post subject: Reply with quote

x0r wrote:

Why do you lie John? I'm sure you didn't even tell your father that someone with the alias of x0r told him he's a bastard over the internet.


Maybe you have misunderstood what I said in the past. My dad isn't in the interest of sueing anybody. ( But that doesn't mean you are released. )

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nog_lorp
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PostPosted: Mon Mar 05, 2007 12:01 am    Post subject: Reply with quote

(er, in reply to john's earlier post) Thanks. I made it all today, relearning all the C I've forgotten (and some new stuff, function pointers=yuck), ran into some snags with uber-shit libraries (rand() increases by 2-4 each time? no matter what seed? How shitty an RNG can you make -_-), and wanted to go to bed Very Happy. Anywho, I figure I'll add some niftier protection and fix that noargument-crash sillieness later.

What I wanted to do was make the important functions reside in dynamically allocated memory, but I was a little scared of how hard that would be (and the lack of resources online). So instead, I made it have several identical functions, made function pointer arrays, and made it pick one semi-randomly each time (its actually seconds modulo 5 -_-, due to issues with rand()). So, if you break in one of those functions, and rerun, it probably won't hit your break. Once you realize that and break on all of them, you still gotta do the math to reverse it. Tomarrow (instead of doing Calculus homework) I think I'll actually try to solve it myself Very Happy.

If you would be so generous, it would be great if you could show me how to have a function residing in dynamically allocated memory.

Cheers,
~nog_lorp

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