how to learn encryption algorithm in easiest way?

Answer 1

I'm not sure whether you mean "Figure out what encryption a given file was done with", or "learn how encryption works", or some other question.

To figure out what it was encrypted with, you usually have to resort to cheating - for instance, many programs will assign a special file extension to stuff they encrypted. There's other tricks as well, but they involve actually understanding cryptography.

Bruce Schneier's book "Applied Cryptography" is generally considered the most accessible book on actually understanding how crypto works. However, I'll warn you, it's a *thick* book, and pretty technical - making crypto that takes more than 5 seconds to break isn't easy. It helps if you have a fair amount of math background....