Introduction to Information Security Chapter II : Classical Ciphers.

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Presentation transcript:

Introduction to Information Security Chapter II : Classical Ciphers

2 1.History of cryptographic research 2.Substitution ciphers Caesar ciphers Affine ciphers Monoalphabetic substitution cipher Homophonic substitution cipher Polyalphabetic substitution cipher Vigenere cipher Hill cipher One-time pad 3.Transposition ciphers Transposition cipher scytale cipher 4.Product ciphers Contents

3 Lec. 4 : History of Cryptologic Research When and how long it was begun? Why?

4 1900BC : Non-standard hieroglyphics 1500BC : Mesopotamian pottery glazes 50BC : Caesar cipher 1518 : Trithemius’ cipher book 1558 : Keys invented 1583 : Vigenere’s book 1790 : Jefferson wheel 1854 : Playfair cipher 1857 : Beaufort’s cipher 1917 : Friedman’s Riverbank Labs 1917 : Vernam one-time pads History of Cryptologic Research

: Hegelin machines 1921 : Hebern machines 1929 : Hill cipher 1973 : Feistel networks 1976 : Public key cryptography 1979 : Secret sharing 1985 : Zero knowledge 1990 : Differential cryptanalysis 1994 : Linear cryptanalysis 1997 : Triple-DES 1998 ~ 2001 : AES History of Cryptologic Research Modern Cryptography

6 History of Cryptologic Research Period Manual Crypto Machine Crypto Modern Crypto Computer Crypto Features Examples ancient ~ ~ 1950 Substitution Transposition Using complex machine Using computer Shannon ’ s theory Scytale, Caesar, Vigenere, Beaufort (USA) Enigma (Germany in 2 nd WW) M-209 (USA in 2 nd WW) DES, SEED, AES RSA, ECC, KCDSA 1950 ~ current

7  Before modern crypto : limited usage –National security, diplomatic, war –Used by limited people –Researched by limited people  Current crypto : widely open, standardized, commerce –Internet, e-commerce –Anybody is using –Research and development by anyone Using Cryptologic Technology

8 Scytale as bc cy dt ea fl ge asas bcbc cycy dtdt eaea flfl gege

9 Enigma(German) vs. Purple

10 Lorenz SZ42 Cipher Machine

11 Classical Encryption Techniques  Basic building blocks of all encryption techniques  Substitution: replacement  Transposition: relocation  Substitution ciphers  Caesar cipher  Monoalphabetic ciphers  Playfair cipher  Hill cipher  Polyalphabetic ciphers: Vigenere cipher  Vernam cipher/One-time pad: perfect cipher  Transposition techniques  Rotor machines: Enigma, Purple

12 2. Substitution Cipher Caesar ciphers Affine ciphers Hill cipher Monoalphabetic substitution cipher Homophonic substitution cipher Polyalphabetic substitution cipher Vigenere cipher One-time pad

13 Caesar Ciphers C = E K (M) = M + K mod 26 K = 3 M = D K (C) = C - K mod 26 K = 3 Mathematically assign numbers to each alphabet Caesar cipher : Julius Caesar, the Roman emperor Also known as shift cipher

14 Caesar Ciphers Define transformation as: Encryption example Weakness Key space is too short – only 26 possible keys Brute force search Example: Break ciphertext “L ORYH LFX"

15 Affine Ciphers Generalization of Caesar cipher Encryption Decryption Example: decrypt the following ciphertext WZDUY ZZYQB OTHTX ZDNZD KWQHI BYQBP WZDUY ZXZDSS How? Using English character frequency analysis…

16 Letter Frequency(%) Letter Frequency(%) Letter Frequency(%) e 12.7 d 4.3 p 1.9 t 9.1 l 4.0 b 1.5 a 8.2 c 2.8 v 1.0 o 7.5 u 2.8 k 0.8 i 7.0 m 2.4 j 0.2 n 6.7 w 2.3 x 0.1 s 6.3 f 2.2 q 0.1 h 6.1 g 2.0 z 0.1 r 6.0 y 2.0 (1) Pr(e)=0.12, (2) Pr(t,a,o,i,n,s,h,r) = 0.06 ~0.09 (3) Pr(d,l)=0.04 (4) Pr(c,u,m,w,f,g,y,p,b)= 0.015~0.023 (5) Pr(v,k,j,x,q,z) <=0.01 English Character Frequencies