I was recently asked how I came up with the idea of "Cyclical Unlock Codes". Well its pretty simple association that frequently ends up being the inventors best friend.
To start off there has been a school of encryption called "compound encoding" where rather than applying an encryption algorithm to individual chunks of data at a time, the data itself is used to encrypt the next chunk of data. This means that you really don't know if you have decrypted any data until you have used the reverse algorithm pretty much to the whole chunk of data you want to protect.
Cyclical unlock codes is the same idea where the first parts of the unlock code are used with different algorithms as the code is built by the computer to make the relatively short length of numbers (which is more convenient for a human to use and repeat) much more secure.
So there... simple... it does sound complicated doesn't it.