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Fundamentals of Information Systems Security by Michael G. Solomon, David 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." Encrypting and decrypting data is a cryptosystem. It usually involves an algorithm, known as a cipher. This combines the original data, known as plaintext, with one or more keys. A key is a string of numbers or characters known only to the sender and/or recipient. The secret message is ciphertext.

The security of a cryptosystem usually depends on the secrecy of the keys rather than the secrecy of the cipher. A strong cryptosystem has a large range of possible keys, making ...

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