What's a good approach for developing a simple serial number generator/verifier?

Question

I\'m working on an app I\'d like to sell some day -- sooner rather than later! I\'d like to develop a reasonably simple serial number scheme to protect it.

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Answer 1

I like @bh213's method, however it isn't going to prevent the key-gens from being fixed as you update your serial number rules.

On a more personal preference note, I prefer the key generator based on a rule set method because if hackers have to patch a binary, you stand to get a bad review on your software because of a bad hacker patch and the ensuing battle between you and hackers.

My preference is based on a universal software truth: Software can and will be hacked if it is popular enough, there is no scheme, no ingenious method that will prevent this from happening. This battle is between the developer who has limited resources and limited time and a hacker group with unlimited time on their hands.

Your key generation scheme is really only to keep the honest customers honest - its easier to get a check cut from Accounts Payable than it is to get Security to sign off on a key generator.