Author:
Fatmike

Language:
C/C++

Upload:
9:01 PM 06/04/2023

Download

Platform
Windows

Difficulty:
4.2

Quality:
5.7

Arch:
x86

Description

..::[FaTmiKE 2o23]::.. After a little break i decided to program another little crackme (This is my 4th crackme). Here are the rules: 1. The main goal is to unpack this crackme or write a loader. 2. If you like, find a valid serial or write a keygen. The crackme was tested on windows 10. Have fun!

• Comments
• Solutions

Ben_Lolo on 2:41 AM 06/09/2023: I love to see a crackme that's as polished as this. MINOR SPOILERS: I'm taking this slowly as a learning experience on how to handle more difficult crackmes. I've followed the control flow up to the function at 0x404C00 and I have a feeling I know where it's going with the debugging and unpacking. If I'm correct and it's not a red herring, then it's a very interesting technique that I've not considered before now. Also challenging!

MARI0x83 on 12:07 PM 06/11/2023: Windows Defender does not like your crack me

Fatmike on 3:24 PM 06/11/2023: I know, but what can i do? It's because protections often use similiar techniques as malware do. You can either trust me, or use a vm to debug the crackme-

Ben_Lolo on 12:48 AM 06/23/2023: I feel like I'm so close to writing a keygen. All that's left now is some nitty-gritty reverse engineering to figure out how the name/serial pair is checked. I've been able to "unpack" it in the sense that I can debug the code after it's been unpacked and that I can extract the memory that contains the unpacked code. I think that's as far as I'll take the unpacking, since the method used seems like a royal pain to write an unpacker or loader for. MAJOR SPOILERS: So far I've found these things: - The name must be 4-8 alphanumeric characters. - The serial is 8 hexadecimal characters. - The conditional jump at +0x12F2 in the unpacked section is what chooses the "good" or "bad" sound. Now I need to figure out how the calls at +0x1B5B and +0x1B69 determine the input as correct. I've found calls to memcpy and memcmp that seem interesting, but we'll see.

timotei_ on 7:07 PM 06/28/2023: First of all, this crackme wins the award for the best user interface and excellent coding style. Furthermore, it comes with some anti-debug tricks and a really sophisticated algo. You really need reversing skills for that and a complete understanding of the code. The challenge among other is that the name is generated based on the serial and not as usual the other way around. I did not manage to fully understand/reverse the code, but was able to generate a name/serial combination: Name: DDDI Serial: 747474745 Thanks Fatmike for that nice crackme! It reminds me on the old days... ;-)

Fatmike on 4:07 PM 10/30/2024: @Everyone : Thank you for your comments and feedback :) @Yanderome : Thanks for your solution, it was fun reading it!

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