Given the length of Windows serial keys is not that long, why couldn't one extract the check function and run an iteration attack to generate valid keys?
Edit: @ale42: makes sense, thanks for putting this one to rest. 36^25 is approximately 8 x 10^38 which is a really, really big number.
Edit: @ale42: makes sense, thanks for putting this one to rest. 36^25 is approximately 8 x 10^38 which is a really, really big number.