MCS 150 Cryptanalysis Exam 2
Monday, January 15
This will be a closed-book exam.
You may, however, use one new 3"-by-5" note card,
last exam's note card, and a calculator.
Cryptanalysis aids, such as tables of characteristic frequencies
and Vigenere tableaux,
will be provided.
You will have the entire class period to work the exam,
but you should not need all that time.
You should be prepared to solve problems of the following kinds.
- Encipher a message by...
- keyword-mixed monoalphabet
- Vigenere polyalphabet (with normal plain and cipher sequences)
given a keyword.
- autokey with priming key letter
- Decipher a "crypt" that was enciphered by...
- keyword-mixed monoalphabet
- Vigenere polyalphabet (with normal plain and cipher sequences)
with alphabets selected by a keyword
- autokey with priming key letter
- Solve (cryptanalyze) an enciphered message enciphered by...
- keyword-mixed monoalphabet
You should be able to this in both these cases:
- crypts with word divisions preserved ("Aristocrats")
- crypts without word divisions ("Patristocrats")
- Vigenere polyalphabet (with normal plain and cipher sequences)
with alphabets selected by a keyword
...without knowing the key in advance.
- Demonstrate your ability to carry out preliminary cryptanalysis tasks
such as ...
- preparing a monoalphabetic frequency distribution
- calculating an index of coincidence
- preparing a trigraphic frequency distribution
- developing "Kasiski" (repeated sequence) evidence
- distinguishing monoalphabets from polyalphabets
- determining the length of the keyword for polyalphabetic
encipherment
- using "slides"/matching frequency distributions
- using a probable word attack
... and using the results.
- Answer questions about chapter 2 of The Code Book,
"Le Chiffre Indechiffrable," including
- What is a homophonic substitution cipher?
- What was the Great Cipher?
- What was "le chiffre indechiffrable"?
- What contributions did Charles Babbage and Friedrich Kasiski
make to cryptanalytic techniques?
- What are the Beale ciphers?
Primary references: your class notes, Sinkov chapter 2
(especially section 2.3),
Sinkov chapter 3 (sections 3.1-3.7, especially 3.1-3.4),
and Singh chapter 2.
Return home.