Section 1 Security (1)5443575432657.pptx

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1. Section 1 Cryptography Symmetric Encryption Ceaser Cipher

2. Types Of Security Computer Security : A Generic name for the collection of tools designed to protect data and to thwart hackers Network Security : measures to protect data during their transmission Internet Security : measures to protect data during their transmission over a collection of interconnected networks

3. Cryptology Cryptography The art or science encompassing the principles and methods of transforming message an intelligible into one that is unintelligible, and then retransforming that message back to its original form Plaintext The original intelligible message Cipher text The transformed message Cipher An algorithm for transforming an intelligible message into one that is unintelligible by transposition and/or substitution methods Key Some critical information used by the cipher, known only to the sender & receiver

4. Cryptology Encipher (encode) Process of converting plaintext to ciphertext using a cipher and a key Decipher (decode) The process of converting ciphertext back into plaintext using a cipher and a key Cryptanalysis ( codebreaking ) The study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key. Cryptology The field encompassing both cryptography and cryptanalysis

5. Encryption Message is called Plaintext (P) Key is used to encrypt message (k) Secured Message is called Cipher Text (C) So it gives E(K,P) = C C = E k (P) Encryption Algorithm(ciphering , encrypting, encoding) Secured Message is called Cipher Text (C) Key (same key above) is used to decrypt message (k) And results the Original Message (P) (Plaintext) So it gives D(C,K) = P P = D k (C) Decryption Algorithm(decrypting, decoding)

6. Symmetric Security Model (Symmetric)

7. Cryptanalysis Brute-force attack Always theoretically possible to simply try every key Most basic attack, directly proportional to key size Assume either know or can recognize when plaintext is found

8. Encryption Techniques

9. Caesar cipher 2000 years ago, by Julius Caesar A simple substitution cipher, known as Caesar cipher Replace each letter with the letter standing 3 places further down the alphabet Plain: meet me after the toga party Cipher: PHHW PH DIWHU WKH WRJD SDUWB No key, just one mapping (translation) 0123456... Plain: abcdefghijklmnopqrstuvwxyz Cipher: DEFGHIJKLMNOPQRSTUVWXYZABC 3456789... c i =E(3,p i )=(p i +3) mod 26; p i =D(3,c i )=(c i -3) mod 26

10. General Ceaser Cipher Can use any shift from 1 to 25, i.e., replace each letter by a letter a fixed distance away c i =E( k,p i )=( p i +k ) mod 26; p i =D( k,c i )=( c i -k) mod 26 Cipher text only attack Characteristics for success The encryption and decryption algorithms are known There are only 25 keys to try The language of the plaintext is known and easily recognizable