I made a software and I would like to distribute it as a demo that can be registered. I would like to know if there is a site where I can offer some reward for some one try to crack my software and explain how it was done. Thanks
Don't spend a lot of money on this effort, because any software you distribute can be cracked. Unless you're distributing expensive hardware keys, or creating a server-side component, any end-user copy protection scheme can be broken.
Instead, you can make it complex enough to thwart most people (it sounds like you've already done this.) Also, you could appeal to your users to be trustworthy and not to share copies. Relying on a service to perform an important feature works for products like Microsoft's Office365.