SHA-1 checksum vs .exe obfuscation

rmmarsh
rmmarsh used Ask the Experts™
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I have a Windows app that has been compromised (hacked).  I am looking at obfuscation but was wondering if generating a SHA-1 checksum and then checking it from within the program would suffice as far as letting me know the app has been compromised.

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File hashing will let you know whether or not it is different to known hashes for that file. However, it won't tell you what has changed or how it was done.

What do you mean when you say it "has been compromised"? How do you know?

Author

Commented:
The guy has access to functions that are only available with a license, which he has not purchased.  I send a response to his email saying something was not working as it should, and I responded that he shouldn't even have access to that function... haven't heard from him since. :D

So, will it tell me if the program has been reverse-engineered?  (i.e. using .NET Reflector).  Is obfuscation better? (like Crypto Obfuscator)
I think it's almost certain that it has been reverse engineered and/or the application has been patched in order to grant access to locked functionality. File hashing will definitely tell you if the file has been patched.
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Author

Commented:
So, I guess I better byte the bullet for $150 USD and buy the obfuscator...   thanks for your insight.
There is a good article here on how to go about securing .NET code:
http://msdn.microsoft.com/en-us/magazine/cc164058.aspx

Author

Commented:
I saw that, plus a few others... settled on Crypto Obfuscation for .NET... seems to be the most comprehensive, plus they answered my emails right away... I like good support! :D  

Thanks again...
ozo
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Commented:
If the app can be compromised, what prevents the SHA checking within the program from being compromised?

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