Book Ciphers

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• Misc
  • Final
    • Tuesday, December 20, Noon to 2:30
    • This room
    • Questions re cryptography we covered, fine-grained writing skills, etc. (like midterm)
    • Rules and format similar to midterm, especially open references
    • Designed for 1 1/2 to 2 hours, you have 2 1/2
    • Donuts and cider
  • SOFIs: 3 responses (15%) as of this morning
• Questions?
  • Portfolio reflections will probably be around 2 pages
• Book Ciphers
  • i.e., the kind of cipher in “The Beale Papers”
  • How do they work?
    • Number the words in some book
    • Ciphertext is series of numbers identifying words in book
    • Plaintext is 1st letter of word at that number in book
  • Check Beale document 2 against Declaration of Independence
    • Numbers: 115 73 24 807 37 52 49 17 31 62 647 22 7 15 140
    • Corresponding letters: I H A V E D E P O S I T E D I
  • Try your own
    • In teams of 4 - 5, agree on a text to use as a key
    • Then split into 2 sub-teams and try to send each other messages
    • Front Team:
      • 14, 53, 9, 155, 169, 144, 9, 154, 25, 12, 16
      • 34 4 12 368 93 197 344 386 161 133 16 52 2 77 311 198 210 103 322 153 22 438 229 478 372 614 7 2045
    • Back Team:
      • 2 6 47 33 87 175 2 11 47 3 43
      • I HATE FINALS
      • 115 640 801 588 85 760 401 607 24 158 174
      • I H A T E F I N A L S
    • Comments/observations
      • Sender and receiver have to use identical keys, e.g., team that used lyrics to a song that turned out to have several different versions
      • There are fine points to counting words, e.g., whether a hyphenated word counts as one or two
      • Key exchange is still a problem
• Next
  • Modern cryptography (especially public key and RSA)

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