MCS 150 Cryptanalysis Exam 3
Exam 3: Monday, January 22
This will be a closed-book and closed-notes exam.
You may, however, use one new
3"-by-5" note card with anything you want written on it
and 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/decipher Playfair messages based on a 5-by-5 square
constructed from a keyword.
- Encipher/decipher messages using Hill's digraphic system.
- Solve crypts in Hill's digraphic system.
- Do modular arithmetic/algebra.
- Carry out matrix operations,
particularly multiplying and finding inverses,
especially modulo 26.
- Use the Euclidean algorithm to find the greatest common divisor,
or gcd, of two positive integers--n and d, say--and to find integers
s and t such that sn + td = gcd(n,d).
- Solve linear congruences like a x = b (mod m).
- Do the modular arithmetic involved in the RSA system.
- Tell about the difference between symmetric and asymmetric ciphers.
- Encipher/decipher simple RSA ciphers.
- Answer questions about Enigma/"Decoding Nazi Secrets."
Primary references for study are your class notes and Sinkov chapter 4.
Secondary references are Singh [chapters 3 (part), 4, and 6]
and the video "Decoding Nazi Secrets."
Last updated 1/18/07
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