MCS 150 Cryptanalysis Exam 1
Exam 1: Monday, January 13
This will be a closed-book and closed-notes exam.
You may, however, use a calculator.
Cryptanalysis aids, such as tables of characteristic frequencies,
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...
- 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.
You should be able to this in both these cases:
- crypts with word divisions preserved
- crypts 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
- determining the number of solutions in {1, ..., m} of
a linear congruence, a x = b (mod m)
- solving a x = b (mod m).
Primary references for study are your class notes and Sinkov chapters
1 and 2.
A supplementary reference is Lewand sections 1.2-1.6.
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