SecurityDec1

# SecurityDec1 - Security and Protection The Security...

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Security and Protection

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The Security Environment Threats Security goals and threats
Basics of Cryptography Relationship between the plaintext and the ciphertext

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Monoalphabetic substitution each letter replaced by different letter Given the encryption key, easy to find decryption key Secret-key crypto called symmetric-key crypto Secret-Key Cryptography
Public-Key Cryptography All users pick a public key/private key pair publish the public key private key not published Public key is the encryption key private key is the decryption key

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To find a key pair e , d : 1. Choose two large prime numbers, P and Q (each greater than 10100), and form: N = P x Q Z = (P–1) x (Q–1) 2. For d choose any number that is relatively prime with Z (that is, such that d has no common factors with Z ). We illustrate the computations involved using small integer values for P and Q: P = 13, Q = 17 –> N = 221, Z = 192 d = 5 3. To find e solve the equation: e x d = 1 mod Z That is, e x d is the smallest element divisible by d in the series Z +1, 2 Z +1, 3 Z +1, . .. . e x d
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## This document was uploaded on 10/15/2010.

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SecurityDec1 - Security and Protection The Security...

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