Spring 2020: Cryptography (Math 481/581)


Instructor Dr. Armin Straub
MSPB 313
(251) 460-7262 (please use e-mail whenever possible)
Office hours MWF, 9-11am, or by appointment
Lecture MWF, 1:25-2:15pm, in MSPB 235
Midterm exams The tentative dates for our two midterm exams are:
Wednesday, February 26
Wednesday, April 8
Final exam Wednesday, May 6 — 1:00-3:00pm
Online grades USAonline
Syllabus syllabus.pdf

Lecture sketches and homework

To help you study for this class, I am posting lecture sketches. These are not a substitute for your personal lecture notes or coming to class (for instance, lots of details and motivation are not included in the sketches). I hope that they are useful to you for revisiting the material and for preparing for exams.

After most classes, homework is assigned and posted below.

  • You should aim to complete the problems right after class, and before the next class meets.
    A 15% penalty applies if homework is submitted after the posted due date.
  • Homework is submitted online, and you have an unlimited number of attempts. Only the best score is used for your grade.
    Most problems have a random component (which allows you to continue practicing throughout the semester without putting your scores at risk).
  • Collect a bonus point for each mathematical typo you find in the lecture notes (that is not yet fixed online), or by reporting mistakes in the homework system. Each bonus point is worth 1% towards a midterm exam.
    The homework system is written by myself in the hope that you find it beneficial. Please help make it as useful as possible by letting me know about any issues!
Date Sketch Homework
01/13 lecture01.pdf Homework Set 1: Problems 1-6 (due 1/24)
01/15 lecture02.pdf Homework Set 1: Problems 7-9 (due 1/24)
The first homework set is now complete, so the due date is final.
01/17 lecture03.pdf Homework Set 2: Problems 1-4 (due 2/3)
01/22 lecture04.pdf Homework Set 2: Problem 5 (due 2/3)
01/24 lecture05.pdf Homework Set 2: Problems 6-11 (due 2/3)
This homework set is now complete, so the due date is final.
01/27 lecture06.pdf Homework Set 3: Problems 1-2 (due 2/10)
01/29 lecture07.pdf Homework Set 3: Problem 3 (due 2/10)
01/31 lecture08.pdf Homework Set 3: Problem 4 (due 2/10)
02/03 lecture09.pdf Homework Set 3: Problem 5 (due 2/10)
This homework set is now complete, so the due date is final.
02/05 lecture10.pdf Homework Set 4: Problems 1-2 (due 2/17)
02/07 lecture11.pdf Homework Set 4: Problems 3-4 (due 2/17)
02/10 lecture12.pdf Homework Set 4: Problems 5-9 (due 2/17)
This homework set is now complete, so the due date is final.
02/12 lecture13.pdf new homework next time
02/14 lecture14.pdf Homework Set 5: Problem 1 (due 2/24)
02/17 lecture15.pdf Homework Set 5: Problem 2 (due 2/24)
start preparing for the midterm exam on 2/26:
midterm01-practice-lecture.pdf (compiled from lectures)
Online practice problems (compiled from homework)
midterm01-practice.pdf (solutions below)


For more involved calculations, we will explore the open-source free computer algebra system Sage.

If you just want to run a handful quick computations (without saving your work), you can use the text box below.

An easy way to use Sage more seriously is by creating an account at This free cloud service does not require you to install anything, and you can access your files and computations from any computer as long as you have internet. To do computations, once you are logged in and inside a project, you will need to create a "Sage notebook" as a new file.

Exams and practice material

There will be two in-class midterm exams and a comprehensive final exam. Notes, books, calculators or computers are not allowed during any of the exams. The exam schedule is posted in the syllabus and at the top of this page.

The following material will help you prepare for the exams.