Information Security Resources

Entries Tagged ‘ciphertext’

Firewall: The Realization of a Company’s Internet and Network Access Policy

The original definition of a firewall is: “a partition made of fireproof material to prevent the spread of a fire from one part of a building or ship to another or to isolate an engine compartment, as on a plane, automobile, etc.” 1 Today, in the computer world, the term refers to any piece of […]

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Cryptography – Revisited

Cryptography, or cryptology, derived from the Greek words for “hidden” writing or speaking, is the practice and study of hiding information. Until modern times, cryptography referred almost exclusively to encryption, the process of converting ordinary information (plain text) into unintelligible gibberish (confidentiality). Cryptography is now considered to be a branch of both mathematics and computer […]

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XOR and the One-Time Pad

Some of my students have asked why we always use XOR (Exclusive OR) in encrypting plaintext into ciphertext. To answer this question, please take a look first at the output of the various combinations of inputs for XOR function. Input A Input B A XOR B 1 1 0 1 0 1 0 1 1 […]

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