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

As Redbeard 0x0A is correct, CD-Keys are to keep honest customers honest. It just needs to be slightly less difficult to buy your product than to find a keygen.

If you are selling your product online, then the best way to do it is to give them a file containing the serial. This way the serial can be however long you want and your paying customers don't have to waste time entering a serial.

A serial scheme can be very simple:

1. Have a large serial space (25 alpha numeric is about 10⁴⁴, but just use a serial file and do 80 char x 16 rows for a key space of 10²³¹¹)
2. Select a few rules to reduce valid serial number space to 100 times what you think you will sell in your wildest dreams

If your product has an online component (like how games have multiplayer online), you could further reduce valid serial numbers using a cryptographically strong random number generator (to select a subset of the rule based keys, product uses rule to check serial, server uses final true serial list). When your product requests service from your server, the server can check the serial.