RCE Endeavors 😅

January 14, 2011

Five Minute Cracking: Hardcoded Expirations

Filed under: General x86-64,Reverse Engineering — admin @ 3:18 AM

I use a specific application (which won’t be named here) quite often. One of the annoying things about this application is that it is classified as shareware and continually pops up a nag screen on each instance to register, authenticate, and/or funnel money to them. Although the application still runs fine when this nag screen is closed — probably due to the developers taking a very fatalistic view on cracking, or them wanting to give their application more exposure (especially since free and possibly better alternatives exist). Admittedly, this screen becomes very annoying to see time and time again. Instead of switching over to the free alternative, I wanted to see how the nag screen works. Upon installation, there is a 40 day trial period that you, as a user, get to use this application. After this period is up, the nag screen begins to appear at each instance. This made me wonder what lengths the application goes to see if the user is using an expired version. I did a search for 40 in hex as 28h to see whether any comparisons come up with that value. Immediately something of interest popped up (string parameter blacked out since it identifies the program):
It immediately shows that the value in eax is compared against 28h and the jump to loc_1400942AF is taken if the value is greater. loc_1400942AF is cross referenced only once in the entire application (from the jump to it above), and it pops up a dialog with DialogBoxParam. This is literally the extent of the protection scheme of the application. Filling the jg instruction with NOPs is all that it takes to defeat it. Alternatively, it is possible to remove the dialog with a resource editor, which may be the simpler method since it doesn’t require looking at x86-64 ASM. The funny thing is that the application has a slightly complex key validation algorithm so writing a keygen for it would take a bit of time and skill; but since it is offered as a full version download (no removed features), keygenning it would be a bit pointless when you can NOP out an instruction. Why the application is designed this way remains a mystery, but it could be related to what I said above about piracy being inevitable and the developers wanting more exposure for their application versus (fully) free alternatives.

1 Comment »

  1. Looks like winrar to me…

    Comment by Jim — June 28, 2014 @ 12:28 AM

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