How to Decrypt DVD's or Blu-Ray Discs?

Which kind of technical knowledge are necessary to know how to create a program by yourself that can decrypt dvd's and blu-ray discs?

Its so hard to do it? So deep or specifical knowledge are needed?

For example, if I buy one dvd for myself and I want to study all its protection's mechanism, how to start? To see how that protection works and how to defeat them?

I mean, how AnyDVD or DVDFab 's team staff "study" all the dvd's and blu-rays released on the market, analyse and discover all the ways to decrypt them?

Thanks.