promix17's Primitive Math
| Download Primitive_Math.zip, 169 kb (password: crackmes.de) Browse contents of Primitive_Math.zip Primitive Math v1.0
Difficulty: 5 - Professional problem to solve | RatingWaiting for at least 3 votes View profile of promix17 » |
Solutions
Solution by tamaroth, published 08. apr, 2011; download (5 kb), password: crackmes.de or browse.
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Solution by Dcoder, published 07. apr, 2011; download (260 kb), password: crackmes.de or browse.
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Discussion and comments
| tamaroth Moderator 31. Mar 2011 | I think there's a small error in your code in the middle of checking routine. After you've checked first two characters of serial, you then proceed do next function. This function is decrypted with a byte (let's call it a key) equal to some form of crc of code. The value should be 0x5D, and when first time it's decoded, everything works fine. But unfortunetaly at the end of the procedure you crypt it again, this time with the key equal 0x2B, and thus on next time, when checking the code, crackme decrypts the code wrongly and you end up with a crashed crackme. example: tamaroth EO34567890103 run it and click check twice, after second click it will crash :( One more thing, you should take care of this additional process you create, after you exit from the crackme it persists in system, you are also able to run multiple copies of that process (good idea would be to check mutex or smth like that) Despite this, I've patched my version with proper values and I'm going further, so far it was fun :) |
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| promix17 Author 01. Apr 2011 | Yes, there is small bug. It may be so, becouse I started coding programm with C++ and finished with OllyDbg, so didn't notice this part of code...I only can say, that this bug can't appear in practice when you are legal user. I think a lot about additional process but again have a mistake. It should end in a minute but it doesn't... And about mutexs: if you use a mutex, when you kill process mutex doesn't dissappeared -> so next time additional process won't run. But the most interesting will be later. Really the idea of crackme let me even show you source code, but whith additional protection it will be more harder))) |
| tamaroth Moderator 01. Apr 2011 | If you assume that you enter the correct serial once, then yes, I agree. But it's rather dangerous bug for a legal software :) And about mutexes: when process ends, you should kill mutex you control, so you can run the program again :) |
| promix17 Author 08. Apr 2011 | Thanks for all solutions. Next time I will try harder and qualitative. |
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