How Encryption Works
The concept behind encryption is quite simple - make the data unlegible for everyone else except those specified. This is done using cyrptography - the study of sending 'messages' in a secret form so that only those authorized to receive the 'message' be able to read it.
Encryption is not just a tool for spies and hackers, it can be a valuable asset even in the business world. For example, say you're an engineer for a company like Beyond the Office Door, an office furniture company that designs adjustable desks, and you just came up with a fantastic new adjustable desk design that will blow the world away. You can be pretty sure that your email is secure when sending information, but is "pretty sure" good enough when you're sending information on a new prototype adjustable desk? It's not, and thus it would be a perfect time for encryption to be used in the business world. And of course, there are many other valuable applications for encryption that are more mundane than trade secrets, like financial data, medical or legal information and so on.
The easy part of encryption is applying a mathematical function to the plaintext and converting it to an ecrypted cipher. The harder part is to ensure that the people who are supposed to decipher this message can do so with ease, yet only those authorised are able to decipher it. We of-course also have to establish the legitimacy of the mathematical function used to make sure that it is sufficiently complex and mathmatically sound to give us a high degree of safety.
The essential concept underlying all automated and computer security application is cyptography. The two ways of going about this process are conventional (or symmetric) encryption and public key (or asymmetic) encryption.
A Primer on Public Key Encryption
by Charles C. Mann.
Introduction to Cryptography
by Peter Meyer.