4.0 Basics of Cryptography
The Security+ exam expects you to have a moderate grounding in both the theory and practice of cryptography and its applications on todays networks. While we wont make you an expert in this subject in a single chapter, we can shed some light on this esoteric subject which should enable you to make better decisions regarding when to employ cryptography, what type to use in specific circumstances, and what is involved in administering crypto-based systems.
Cryptography involves creating and using systems to encode (or encrypt) data, allowing it to be read (decrypted) only by those who have certain knowledge (like the type of encryption used, and the specific key used).
Cryptography has a long history. To cite the example mentioned in the Cryptography FAQ385, legend has it that Julius Caesar had to send messages to his trusted compatriots via messengers he didnt trust. In order to protect the contents of the messages, he used a substitution code, replacing each letter by the one 3 positions after it A by D, B by E, C by F and so on and only those who knew the substitution rule were able to decipher the messages. Despite this history, advances in cryptography are still being made today. The Security+ exam expects you to know about both traditional symmetric cryptography techniques as well as the newer asymmetric techniques that are only now becoming widely used.
386. Schneier, Bruce, Applied Cryptography: Protocols, Algorithms and Source Code in C, 2nd Edition, John Wiley, November, 1995, http://www.nerdbooks.com/item.html?id=0471117099
387. Kaufman, Charlie, Radia Perlman and Mike Speciner, Network Security: Private Communication in a Public World, 2nd Edition, Prentice-Hall, April, 2002, http://www.nerdbooks.com/item.html?id=0130460192
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