MCS 150 Cryptanalysis Exam 1
Exam 1: Tuesday, January 8
This will be a closed-book and closed-notes exam.
You may, however, use one 3"-by-5" note card and a calculator.
Cryptanalysis aids, such as tables of characteristic frequencies,
will be provided.
You will have the entire two-hour 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...
- direct standard alphabet (additive cipher)
- decimation (multiplicative cipher)
- linear transformation (affine transformation)
- keyword-based monoalphabetic encipherment
- symbol-based monoalphabetic encipherment.
- Decipher a "crypt" that was enciphered by...
- direct standard alphabet (additive cipher)
- decimations (multiplicative cipher)
- linear transformation (affine transformation)
- keyword-based monoalphabetic encipherment
- symbol-based monoalphabetic encipherment.
- Solve (cryptanalyze) an enciphered message enciphered by...
- direct standard alphabet (additive cipher)
- decimations (multiplicative cipher)
- linear transformation (affine transformation)
- keyword-based monoalphabetic encipherment
- symbol-based monoalphabetic encipherment
...without knowing the key in advance.
The cryptograms in this exam will be "aristocrats,"
i.e., monoalphabetic encipherments with word divisions preserved.
On the next exam you may have to deal with "patristocrats,"
i.e., monoalphabetic encipherments without word divisions.
- Demonstrate your ability to carry out preliminary cryptanalysis tasks
like preparing a ...
- monoalphabetic frequency distribution
- trigraph frequency distribution
and using the results.
- Solve problems in modular arithmetic and modular algebra,
including
- finding the equivalent (residue) of a number modulo m
- finding the reciprocal (multiplicative inverse) of a
number modulo m
- solving C = a P + b (mod m) for P, or vice versa
- Answer questions about chapter 1 of The Code Book,
"The Cipher of Mary Queen of Scots."
- What is the story of cryptanalysis and Mary Queen of Scots?
- Terminology: steganography, cryptography; transposition,
substitution; code, encode, decode; cipher, encipher, decipher;
encrypt, decrypt; crypto-algorithm, key
- Kerckhoff's Principle
- What people invented cryptanalysis, according to Singh?
When?
Primary references for study are your class notes and Sinkov chapters
1 and 2.
A supplementary reference is Simon Singh's The Code Book,
chapter 1.
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