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Fundamentals of Information Systems Security, 3rd Edition by Kim

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CHAPTER 9: Cryptography

ACCORDING TO Webster’s Revised Unabridged Dictionary, cryptography is “the act or art of writing in secret characters.” The Free Online Dictionary of Computing says cryptography is “encoding data so that it can only be decoded by specific individuals.” The algorithms, or ciphers, used to encrypt and decrypt data are collectively called a cryptosystem. Most ciphers take unencrypted data, called plaintext, and use one or more keys to transform the plaintext into a secret message. A key is a string of numbers or characters known only to the sender and/or recipient. The resulting secret message is ciphertext.

The security of a cryptosystem usually depends on the secrecy of the keys rather than the secrecy of the cipher. ...

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