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CISSP Training Kit by David R. Miller

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Historical review of cryptography

Cryptography has been around for thousands of years. For almost all that time, there were only symmetric key ciphers, in which the key used to encrypt the message was exactly the same key used to decrypt the message. It was only when computers became commonplace (in the 1970s) that the computational horsepower was available to crunch numbers large enough to allow the invention of asymmetric key ciphers. Asymmetric key ciphers use two keys, a public key and a private key, that are mathematically related, and the content that one key encrypts can be decrypted only by the other key. The focus of this chapter will be the analysis of these symmetric and asymmetric key ciphers and cryptosystems.

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