1 / 14

History

Online Cryptography Course Dan Boneh. Introduction. History. History. David Kahn, “The code breakers” (1996). Symmetric Ciphers. Few Historic Examples (all badly broken). 1. Substitution cipher. k := . Caesar Cipher (no key).

takoda
Download Presentation

History

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Online Cryptography Course Dan Boneh Introduction History

  2. History David Kahn, “The code breakers” (1996)

  3. Symmetric Ciphers

  4. Few Historic Examples (all badly broken) 1. Substitution cipher k :=

  5. Caesar Cipher (no key)

  6. Whatis the size of key space in the substitution cipher assuming 26 letters? 26 factorial)

  7. How to break a substitution cipher? What is the most common letter in English text? “X” “L” “E” “H”

  8. How to break a substitution cipher? • Use frequency of English letters • Use frequency of pairs of letters (digrams)

  9. An Example UKBYBIPOUZBCUFEEBORUKBYBHOBBRFESPVKBWFOFERVNBCVBZPRUBOFERVNBCVBPCYYFVUFOFEIKNWFRFIKJNUPWRFIPOUNVNIPUBRNCUKBEFWWFDNCHXCYBOHOPYXPUBNCUBOYNRVNIWNCPOJIOFHOPZRVFZIXUBORJRUBZRBCHNCBBONCHRJZSFWNVRJRUBZRPCYZPUKBZPUNVPWPCYVFZIXUPUNFCPWRVNBCVBRPYYNUNFCPWWJUKBYBIPOUZBCUIPOUNVNIPUBRNCHOPYXPUBNCUBOYNRVNIWNCPOJIOFHOPZRNCRVNBCUNENVVFZIXUNCHPCYVFZIXUPUNFCPWZPUKBZPUNVR E IN THE AT T A trigrams digrams

  10. 2. Vigener cipher (16’th century, Rome) k = C R Y P T O C R Y P T O C R Y P T (+ mod 26) m = W H A T A N I C E D A Y T O D A Y c = Z Z Z J U C L U D T U N W G C Q S suppose most common = “H” first letter of key = “H” – “E” = “C”

  11. 3. Rotor Machines (1870-1943) Early example: the Hebern machine (single rotor) A B C . . X Y Z K S T . . R N E E K S T . . R N N E K S T . . R key

  12. Rotor Machines (cont.) Most famous: the Enigma (3-5 rotors) # keys = 264 = 218 (actually 236 due to plugboard)

  13. 4. Data Encryption Standard (1974) DES: # keys = 256 , block size = 64 bits Today: AES (2001), Salsa20 (2008)(and many others)

  14. End of Segment

More Related