69 lines
2.1 KiB
Typst
69 lines
2.1 KiB
Typst
#let post_slug = "crackmes-license-checker"
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#let post_preview_image = "cover.png"
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#let post_summary = "Reverse engineering license-checker from crackmes.one"
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= Crackmes.one license-checker solution
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= Solution 1
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First get a feel for the program.
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```sh
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$ ./license_checker_1
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Usage : ./license_checker_1 <license key here>
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./license_checker_1 12345
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12345 is not a valid license key.
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```
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Open it up in binary-ninja and go to the main function:
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#image("/static/posts/crackmes-license-checker/image.png")
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Notice the key is visible, so strings would have worked here too.
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```c
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if (!strcmp(arg2[1], "KS-LICENSE-KEY-2021-REV-1", "KS-LICENSE-KEY-2021-REV-1"))
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{
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puts("
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Congratulations ! You have successfully registered your premium service.");
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exit(0);
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}
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```
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Immediately the keys are visible. Trying it:
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```sh
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$ ./license_checker_1 KS-LICENSE-KEY-2021-REV-1
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Congratulations ! You have successfully registered your premium service.
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```
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Looking at the program, what it does is verify the right number of inputs are present, and test the inputs against a known string.
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= Solution 2
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The fastest solution would have been to use strings:
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```sh
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$ strings license_checker_1 | grep -v '\.' | grep -v '_'
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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XXXXXXXXXXXXXXXXXXXXXXXXXXXX
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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exit
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puts
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printf
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strcmp
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u3UH
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Usage : %s <license key here>
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KS-LICENSE-KEY-2021-REV-1
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;*3$"
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main
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```
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Here it's easy to guess which of these results is the key.
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= Notes
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Author: NomanProdhan\
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Challenge Link: https://crackmes.one/crackme/619eda7b33c5d455dece628d\
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Description:\
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This is a simple license checker made with C. This is for complete beginners.
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I'm new to "crackmes" this so the challenge description feels appropriate to try.
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I used binary-ninja-free. It feels much cleaner than IDA-free or ghidra which I've used for CTF's in the past. Very much overkill for this challenge though. |