Manifest: Monday 4 September 2000

Assignments Due
Monday, 11 September	Problem Set 1
Monday, 18 September	Projects Preliminary Proposal

Readings
Read before 6 September: Stallings, Chapter 3.

Optional reading for more information: (see web version for links)

• Claude Shannon, Communication Theory of Secrecy Systems, 1949. (Original paper as images.)
• Alex Biryukov's lecture notes on cryptanalysis of Enigma
• Alan Turing's Treatise on Enigma (1940, declassified in 1996)
• Breaking the Code (1997 movie with Derek Jacobi)

Vigenere Square

                  1         2         3         4         5
Count:   12345678901234567890123456789012345678901234567890123456         
Plain:   ThebiggerboysmadeciphersbutifIgotholdofafewwordsIusually 
Key:     KEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKE
Cipher:  DLCLMEQIPLSWCQYNIASTFOVQLYRSJGQSRRSJNSDKJCGAMBHQSYQEEJVC
            6         7         8         9        10        11
         7890123456789012345678901234567890123456789012345678901234
Plain:   foundoutthekeyTheconsequenceofthisingenuitywasoccasionally
Key:     YKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEY
Cipher:  DYYLNSSDXFOOCIXFOGMXWCAYCXGCYJRRMQSREORSSXWGEQYGAKWGYRYVPW
             12        13        14        15        16
         5678901234567890123456789012345678901234567890123456789
Plain:   painfultheownersofthedetectedcipherssometimesthrashedme
Key:     KEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYK
Cipher:  ZEGXJSVXFOSUXIPCSDDLCNIROGROHASTFOVQCSKOXGWIQDLPKWFOHKO
        17        18        19        20
         012345678901234567890123456789012345
Plain:   thoughthefaultlayintheirownstupidity
Key:     YKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKEYKE
Cipher:  XFYYERXFOJYEPRVEWSRRRIGBSUXWRETGNMRI

Charles Babbage (quoted in Simon Singh,
The Code Book : The Evolution of Secrecy from Mary, Queen of Scots to Quantum Cryptography, 1999)

Questions

• How to attack the Vigenere cipher.
• How do you convince someone a cipher is secure?
• What is a "perfect cipher"?
• How to prove a cipher is perfect.
• How to prove a cipher is imperfect.
• What are entropy, rate, redundancy, and unicity?
• How important is redundancy in cryptology?

Propose to an Englishman any principle, or any instrument, however admirable, and you will observe that the whole effort of the English mind is directed to find a difficulty, a defect, or an impossiblity in it. If you speak to him of a machine for peeling a potato, he will pronounce it impossible: if you peel a potato with it before his eyes, he will declare it useless, because it will not slice a pineapple.

Charles Babbage, breaker of Vigenere cipher, after losing funding for his Difference Engine project, 1823.

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University of Virginia Department of Computer Science CS 551: Security and Privacy on the Internet

David Evans evans@virginia.edu