Study guide for Linguistics 484: Winter 2008

This sheet is a quick summary of what I think would be fair

to test in Wednesday's midterm. If you are on top of most of

this material you'll be fine.

Format will be:

1 compulsory "matching" question. You will need to match

concepts against their definitions. (10 minutes/ 25 points)

Choose any 3 from 7 longer questions. (10 minutes each/ 25 points 

each). There will be two questions based on the "Mathematical

thinking" section below, one from each of the others.

Terminology (for compulsory question)

plaintext - ciphertext - cryptanalysis - monoalphabetic - polyalphabetic - polygraphic.

Syllables (open, closed, onset, nucleus,coda). 

Cartouches. 

Alphabetic.

Logographic. 

Syllabary. 

Abjad.

Index of co-incidence.

Frequency analysis.

Keyword.

Plugboard.

One time pad.

Vigenere

Playfair.

Code. 

Cipher.

Steganography.

Code systems (1 question)

shift cipher, general monoalphabetic, Vigenere, Playfair

(should be able to encode/decode during exam, if you are

 given the key)

Ancient Languages and Writing systems (1 question)

Linear B. Kober grid. Hieroglyphics. 

Rebus principle. 

Hiragana-Katakana-Kanji

Semantic and phonetic aspects of Chinese characters.

Use of keywords (1 question)

Keyword alphabets

Polyalphabetic ciphers with keywords. 

Relevance of repeated words in monoalphabetic ciphers.

Weaknesses of keyword based alphabets (XYZ usually unchanged).

How keywords are used in Playfair.

Mathematical thinking about codes (2 questions)

• How many different shift ciphers? (26)
• How many different monoalphabetic ciphers? (many, show calculation of 26*25*24*... = many)
• How many different monoalphabetic ciphers with keyword alphabet? (many, but fewer than last line)
• Preservation of digraph frequencies in Playfair.
• Patterns in repeats for diagnosing Playfair.
• Index of co-incidence calculation.
• Kasiski repeats, factorization.
• Why it is possible that 99% of ships setting sail across the Atlantic got through, but casualties  among merchant seamen were around 30% by the end of the war.

Enigma (1 question)

 Rotors - Reflector - Plugboard. 

 Two weaknesses of Enigma

   1) Wehrmacht use of message indicator, with random letters   chosen by operator

   2) Guarantee that no letter translates to itself

 Be ready to explain something about why these weaknesses were

 weaknesses.

Military Intelligence (1 question)

Explain why the allies needed to keep secret the fact that Enigma was being broken. Control of distribution via "need to know".  Use of spotter planes to detect subs you already knew

the location of. 

Balance of tactics and intelligence: Crete, Midway, Battle of Atlantic