How to Crack Just About Any Mac App (and How to Prevent It)

How I'd Crack Your Mac App

Well, not you specifically, but by you I mean the average Mac developer. It's too easy to crack Mac apps. Way too easy. By walking through how I can hack your app with only one Terminal shell, I hope to shed some light on how this is most commonly done, and hopefully convince you to protect yourself against me. I'll be ending this article with some tips to prevent this kind of hack.

In order to follow along you're going to need a few command line utilities. You're going to need the Xcode tools installed. And, lastly, you're going to need an app to operate on. I chose Exces, a shareware App I wrote a long time ago.

Let's start by making sure we have the two utilities we need: otx and class-dump. I like to use Homebrew as my package manager of choice. Note that I will use command line utilities only, including vim. If you prefer GUIs, feel free to use your code editor of choice, HexFiend and otx's GUI app.

$ sudo brew install otx
$ sudo brew install class-dump

The first step is to poke into the target app's headers, gentlemanly left intact by the unwitting developer.

$ cd Exces.app/Contents/MacOS
$ class-dump Exces | vim

Browse around, and find the following gem:

@interface SSExcesAppController : NSObject
{
[...]
BOOL registred;
[...]
- (void)verifyLicenseFile:(id)arg1;
- (id)verifyPath:(id)arg1;
- (BOOL)registred;

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