Chapter 7 New

# Chapter 7 New - Data Security Terminology encryption key...

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Data Security

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Terminology:: encryption key encryption decryption plaintext ciphertext encryption algorithm decryption algorithm
Why encrypt?

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Security
Simplest Encryption Technique: Caesar Cipher: Not secure, easy to decipher monoalphabetic cipher

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Polyalphabetic Cipher Similar to caesar cipher except a given plaintext character is not always replaced with the same ciphertext character. We choose a replacement character based not only on the original plaintext character, but also on its position in the message. for (int I = 0; i<length of P; i++) c[i] = p[i] + k +( I mod 3); if k = 1, then 1 is added to ASCII codes in positions 1,4,7, and so on, and 3 is added to codes in positions 2,5,8 and so on. For the string THEMTHENTHEY, the ciphertext (encoded) string would be UJHNVKFPWIG. For example, THE would be encrypted UJF, VKF, and WIG.
Another example of a polyalphabetic cipher is the Vigenere cipher it uses a two dimensional array, each new row is formed by moving each character in the previous row, left one position, with wraparound A given letter is replaced based on its relative position in the message and its relative position in the alphabetic j = P[i] –’A’; C[i] = v[i% 26] [j]

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Transpositional Cipher Arrange your data in a 2-d array of m columns and d rows. Agree on a transpositional cipher of width m which specifies that column m x in plaintext is to be transposed with column m y in ciphertext message
Transpositional Encryption

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Bit leve encryption (ciphering) Use a bit level encryption of length M EXOR M bits of plaintext message with this encryption key and transmit result.
Data Encryption Standards DES Previous methods are neither complex, nor are they very good. long keys are better, but implementation is more difficult Approaches exist that keep the keys short relative to the size of the message and use complex procedures to encrypt the data. DES

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Chapter 7 New - Data Security Terminology encryption key...

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