timotei_'s timotei crackme#5

Author:
timotei_

Language:
Assembler

Upload:
2023-04-18 18:53

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Platform:
Windows

Difficulty:
2.0

Quality:
4.5

Arch:
x86-64

Downloads:
37

Size:
2.50 KB

Writeups:
1

Comments:
10

Description

A crackme for beginners. Get yourself a keyfile or even better create a keyfilemaker. Enjoy!

Comments (10)
Writeups (1)

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MARI0x83 on 2023-04-20 10:27: Does not launch for some reason

timotei_ on 2023-04-21 06:23: @MARI0x83 Correct, it won't start without a valid keyfile :-)

Tyfo on 2023-05-24 08:56: Little spoiler: this program checks the checksum of a file with a certain name. The length of the file must be equal to a certain value, and the content must fit the checksum check (which is equal to the last character). So there are many solutions to this problem. An interesting problem with many solutions. For example, a file with the following content (as hex!): 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 FF 02

hashtan on 2023-07-13 06:51: Can you tell me What is the password of this file.

timotei_ on 2023-07-13 15:05: @hashtan: see FAQ -- https://crackmes.one/faq

infected on 2023-08-25 06:30: Im newbie in RE, sorry for any stupid questions from me. I actually dont quite understand where the hints are that tell me what the keyfile's content should be. I saw the solution but the explanation doesnt convince me. ---SPOILER ALERT--- He/She said "cmp dl,byte ptr ds:[eax]" is checking whether the byte is "0x00" or not. However, the dl register was added in the previous loop, and "byte ptr ds:[eax]" was supposed to be the content of the keyfile. Where was the "0x00" coming from?

timotei_ on 2023-08-25 10:11: infected, thanks for trying my crackme! You are right, the way decribed in the solution only works with "00" as bytestring in keyfile. So the result after adding is "0x00". If you have another bytestring the dl-register will have another value. // Since the comment section isn't moderated it would be better to ask your questions in the discord channel.

infected on 2023-08-25 11:06: I dont know there is a discord channel for discussions, sorry, would you mind sending me the invite link, i still have some questions to ask

timotei_ on 2023-08-25 12:58: Have a look at the crackmes.one startpage, you'll find the invite link there. :-)

hooleyice on 2023-09-16 20:18: I'm new to RE and this thing got me to think for a while. But looks like my solution is the most creative. [SPOILER] I just made all of the 21 bytes sum up to the value of 22nd so all 1-21 are 01 and the 22nd is 15. Also there was some check after but it got out of eax so it just did nothing. Thanks for this crackme, this was pretty cool

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Solution by hacktooth on 2023-04-24 00:10:
Keyfile Generator + text file to explain my steps... + source code

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