MCS 223 Cryptography Exam 1
Exam 1: Friday, January 9
This will be a closed-book 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 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)
Example: the "Atbash" cipher
- Decipher a "crypt" that was enciphered by...
- direct standard alphabet (additive cipher)
- decimations (multiplicative cipher)
- linear transformation (affine transformation)
Example: the "Atbash" cipher
- Solve (cryptanalyze) an enciphered message enciphered by...
- direct standard alphabet (additive cipher)
- decimations (multiplicative cipher)
- linear transformation (affine transformation)
...without knowing the key in advance.
- Demonstrate your ability to carry out preliminary cryptanalysis tasks
like preparing a ...
- monoalphabetic 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).
- Encipher or decipher messages in one of these systems discussed
in Barr's section 1.1, "A Crypto-Chronology":
- Atbash
- Spartan scytale
- Vigenere's autokey
- Pigpen cipher
- Answer basic questions about the video
Codebreakers.
Primary references are your class notes; Sinkov chapter 1;
Barr section 1.1 problems 1-6, 9-11, 14;
and the video Codebreakers.
Secondary references are Barr sections 1.1 and 2.1-2.2.
Return home.