Groupwork homework will be due today, no other homework except to keep on with your studying of Chapter 3 as described in recent daily posts.
Note: please bring a laptop/tablet to class if it is fairly easy for you, I may do an activity that uses them (not sure yet)
Reminder that groupwork homework is due today. No other homework for the day.
To do for today:
- At home, work through as much of the rest of today’s worksheet as you can. It is available here.
In class we’ll take it up and discover more about modular arithmetic.
No particular homework, see you in class. I’ll have your quizzes back and we’ll be doing more number theory.
Mission #2 is due today. We will be continuing basic number theory in class, which is Chapter 3 in Trappe and Washington. We’ll be doing 3.4, 3.5 and 3.6 on Friday and/or Monday.
Today is your first quiz!
It will be a written quiz taking the whole period. It will be closed-book. I will provide such things as the Vigenere square, multiplication table mod 26, english letter frequencies, and alphabet-to-number table, if needed.
- Use the Cryptosystem organizer to study the following cryptosystems (so this means being able to describe things like key space, how to encrypt/decrypt, being able to apply various cryptanalysis techniques). I may ask you to encrypt, decrypt, or cryptanalyse.
- Caesar cipher
- Scytale (no need for any cryptanalysis techniques beyond exhaustive search, but do know the system)
- Substitution cipher (alphabetic substitution)
- Vigenere cipher
- Affine cipher
- Hill cipher
- You should be adept at:
- modular arithmetic
- the notion of invertible element in modular arithmetic, finding inverses by inspection
- the notion of an invertible matrix in modular arithmetic
- notions of divisibility, primes, prime factorization, gcd, lcm
- performing the Euclidean algorithm and using it to find inverses in modular arithmetic (to be covered Friday Sept 2)
- Terminology you should be able to explain:
- coding theory
- plaintext and plaintext space
- ciphertext and ciphertext space
- key and keyspace
- types of cryptanalysis: ciphertext only, known plaintext, chosen plaintext, chosen ciphertext
- confusion (property of cryptosystem)
- diffusion (property of cryptosystem)
- On this quiz we won’t have any proofs, but in future ones, we will.
- You should know the broad outlines of the history, but I won’t test you on it.
Reminder that Mission #1 is due today. See you in class.
Note: Today we will cover the Euclidean algorithm and its use in finding inverses in modular arithmetic. This is to be found in Sections 3.1, 3.2, and 3.3 of your text. They are assigned for reading (with no particular due date, but note: you have a quiz on Wednesday after the holiday weekend).