C Based Key / KeyGen for locking program

The goal for this project is to create a pure-C (no external libraries) key and keygen for use in a small product. The resulting key will be 20 digits and created as 5 groups of 4 numbers. You are delivering a KeyGen program that takes a unique 16 digit number as input and will generate a valid key. The 16 digits comes from another part of my program. The Validation should be done in 3 parts. 1- At one point the general validity of the number is verified using some algorithm that uses the last 4 digits as a checksum for the other groups. This means the last group of numbers can not be a product of the input byte array. 2- A second test uses a hash function (such as sha2) with a combination of the 32 byte key and a private key and verifies the 1st, 2nd and 3rd group of numbers fit the parts of the resulting hash. 3- A final test is run on the 4th group of numbers and I'll let the developer think of how to integrate this. The KeyGen can be C or C++ as long as it's provided as a dll with a simple export. The 3 validation functions must be in C only without any external libraries, although Win32 calls are okay (just not libc). ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Win32