A Brief History of Cryptography

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We use it every day and we rely on it. But what are the roots of cryptography? How were, for example, the ancient Greeks able to protect information from their enemies? In this talk we will go through 5500 years of developing encryption technologies and look at how these work.

From the Un-Distinguished Lecture Series (http://ws.cs.ubc.ca/~udls/). The talk was given Mar. 23, 2007

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A Brief History of Cryptography

  1. 1. A Brief History of Cryptography ______________ Florian Deckert 23.03.2007
  2. 2. Encyclopedia Britannica: “Cryptography: Practice of the enciphering and deciphering of messages in secret code in order to render them unintelligible to all but the intended receiver.” 23.03.2007 Florian Deckert 2
  3. 3. Early Cryptography • 3500 BC: Sumerians – Cuneiform writings 23.03.2007 Florian Deckert 3
  4. 4. Early Cryptography • 1900 BC: Egypt – First known use of cryptography 23.03.2007 Florian Deckert 4
  5. 5. Early Cryptography • 500 – 600 BC: ATBASH Cipher – Used by Hebrew scribes – Substitution cipher (reversed alphabet) 23.03.2007 Florian Deckert 5
  6. 6. Early Cryptography • 486 BC: Greece – σκυτάλη – skytale 23.03.2007 Florian Deckert 6
  7. 7. Early Cryptography • 60 – 50 BC: Julius Caesar – substitution cipher – Shift letters by X positions: • E.g. X = 3: A D, B E, C F, ... – Weakness? • Frequency analysis (1000 AD) – 1466: Leon Albertini: cipher disk • Used until 16th century 23.03.2007 Florian Deckert 7
  8. 8. Medieval Cryptography • 1587: Vigenère Cipher – Polyalphabetic: one to many relationship – Example • Encrypt: lamp • Keyword: ubc • Ciphertext: fboj • Apart from that... 23.03.2007 Florian Deckert 8
  9. 9. Modern Cryptography • 1845: Morse Code – Represention by code signal – States (on and off) composed into 5 symbols 23.03.2007 Florian Deckert 9
  10. 10. Modern Cryptography • 1863: Kasiski breaks Vigenere: – Find length of keyword – Divide message into substitution cryptograms – Use frequency analysis to solve these 23.03.2007 Florian Deckert 10
  11. 11. Modern Cryptography • 1918: ADFGVX Cipher – Used in the German army in WWI A D F G X B T A L P A D H O Z K D Q F V S N F G J C U X G M R E W Y X 23.03.2007 Florian Deckert 11
  12. 12. Modern Cryptography • 1918: The Enigma – Arthur Scherbius – Business: confidential docs – No codebooks – Rotors multi substitution – Wireing changes as-you- type – German forces in WWII – Room 40 23.03.2007 Florian Deckert 12
  13. 13. Modern Cryptography • 1937 – 1945: Navajo Code Talkers 23.03.2007 Florian Deckert 13
  14. 14. Modern Cryptography • 1949: Shannon: – Communication Theory of Secret Systems – Proved: One time pad unbreakable 23.03.2007 Florian Deckert 14
  15. 15. Modern Cryptography • Until mid 70‘s 23.03.2007 Florian Deckert 15
  16. 16. Modern Cryptography • 1976: Diffie – Hellman Key Exchange – Whitfield Diffie and Martin Hellman – Discrete logarithm problem: • G: finite cyclic group with n elements • Modulo n multiplication • b: generator of G: every element g of G can be written as g = bk for some integer k • Goal: find k given g and b and n! • Very hard problem 23.03.2007 Florian Deckert 16
  17. 17. Modern Cryptography • So how does it work? • Exploits? – Man in the middle – Fix: additional authentication 23.03.2007 Florian Deckert 17
  18. 18. Modern Cryptography • Public Key Crypto – Key exchange problem – Asymmetric key algorithm – E.g: RSA, MIT, 1977 23.03.2007 Florian Deckert 18
  19. 19. Modern Cryptography • 1991: PGP Pretty Good Privacy – Protocol, uses RSA – Encryption & decryption – Digital signatures • How does that work? – Web of Trust • Third party signs (public) key to attest association between person and key – Other Possibility: Hierarchical, CA based • E.g.: X.509 Certificates in SSL 23.03.2007 Florian Deckert 19
  20. 20. Thank You! Let’s go to Koerner’s.

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