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Lecture 2 - Class Notes September 11th 2008 Elementary...

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Class Notes: September 11 th , 2008 Elementary Cryptography -Strongest tool to control security threats -Based in higher Math: Analysis, Number Theory, Probability Theory, Statistics -To use it, don’t need to know the mathematical background. Terminology: Sender: Alice Recipient: Bob S entrusts message to transmission medium T. What can Eve do? 1. Even can try to intercept the message 2. Even can try to block the message 3. Eve can modify the message 4. Eve can fabricate a message Encryption addresses all four of these threats. Most fundamental building block of secure computing. Encryption: encoding a message (encode, encipher) Decryption: decoding a message (decode, decipher) Original message: plaintext Encrypted message: cipher text C= E(P) P = D(E(P)) Algorithms often use a key K. Keys allow us to use the same algorithm so that with different keys, we get different output for the same input. Keys allow you to publish algorithms.
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