Spring 2021: 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

Held virtually using Zoom; please make an appointment by email at least 2 hours in advance.

Class schedule MWF, 1:25-2:15pm, in MSPB 235

Due to COVID restrictions, you may only attend those meetings assigned to the cohort you signed up for.

Midterm exams The tentative dates for our two midterm exams are:
Monday, March 1
Wednesday, April 7
Final exam Wednesday, May 5 — 1:00pm-3:00pm
Online grades Homework Scores
Exams: USAonline (Canvas)
Syllabus syllabus.pdf

Assignments and course material

In order to be able to view the lecture recordings, you need to be logged into USAonline (Canvas). If you are still running into access issues, then please view the recordings through Panopto Video in our course page on Canvas.

Dates Assignments and course material
#1 01/20
Homework Set 1 (due 2/1)
Lecture notes:
Class schedule:
01/20: online using pre-recorded lectures
01/22: in-person meeting
01/25: online using pre-recorded lectures
#2 01/27
Homework Set 2 (due 2/8)
Lecture notes:
Class schedule:
01/27: in-person meeting
01/29: in-person meeting
02/01: online using pre-recorded lectures
#3 02/03
Homework Set 3 (due 2/15)
Lecture notes:
Class schedule:
02/03: in-person meeting
02/05: in-person meeting
02/08: online using pre-recorded lectures
#4 02/10
Homework Set 4 (due 2/22)
Lecture notes:
Class schedule:
02/10: in-person meeting
02/12: in-person meeting
02/15: online using pre-recorded lectures
#5 02/17
Homework Set 5 (due 3/1)
Lecture notes:
Class schedule:
02/17: in-person meeting
02/19: in-person meeting
02/22: online using pre-recorded lectures
02/24: in-person meeting
02/26: online via Zoom
zoom-02-26.mp4 (corresponding PDF)
lectures-01-16.pdf (all lecture notes up to now in one big file)
Midterm Exam #1
Midterm Exam #1 format:
#6 03/03
Homework Set 6 (due 3/15)
Lecture notes:
Lecture recordings:
Class schedule:
03/03: in-person meeting
03/05: in-person meeting
03/08: online using pre-recorded lectures
#7 03/10
Lecture notes:
Class schedule:
03/10: student holiday
03/12: in-person meeting
03/15: online using pre-recorded lectures
03/17: in-person meeting
#8 03/19
Lecture notes:
Lecture recordings:
Class schedule:
03/19: in-person meeting
03/22: online using pre-recorded lectures
03/24: in-person meeting
#9 03/26
Lecture notes:
Lecture recordings:
Class schedule:
03/26: in-person meeting
03/29: online using pre-recorded lectures
03/31: in-person meeting
04/02: in-person meeting
04/05: online via Zoom
zoom-04-05.mp4 (corresponding PDF)
lectures-17-29.pdf (all lecture notes since the previous exam in one big file)
Midterm Exam #2
#10 04/09
Lecture notes:
Lecture recordings:
Class schedule:
04/09: in-person meeting
04/12: online using pre-recorded lectures
04/14: in-person meeting
#11 04/16
Lecture notes:
Lecture recordings:
Class schedule:
04/16: in-person meeting
04/19: online using pre-recorded lectures
04/21: in-person meeting
04/23: in-person meeting
04/26: online using pre-recorded lectures
04/28: in-person meeting
04/30: online via Zoom
zoom-04-30.mp4 (corresponding PDF)
lectures-30-37.pdf (all lecture notes since the previous exam in one big file)
Final Exam

About the homework

  • Homework problems are posted for each unit. 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).

  • Aim to complete the problems well before the posted due date.

    A 15% penalty applies if homework is submitted late.

  • 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!


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.

A convenient way to use Sage more seriously is 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.


If you take this class for graduate credit, you need to complete a project. The idea is to gain additional insight into a topic that you are particularly interested in. Some suggestions for projects are listed further below.

  • The outcome of the project should be a short paper (about 4 pages)
    • in which you introduce the topic, and then
    • describe how you explored the topic.
    Here, exploring can mean (but is not limited to)
    • computations or visualizations you did in, say, Sage,
    • working out representative examples, or
    • combining different sources to get an overall picture.

Each project should have either a computational part (this is a great chance to play with Sage!) or have a more mathematical component. Here are some ideas:

  • Compute and investigate the number of Fermat liars and/or strong liars. For instance, a theoretical result states that at most a quarter of the residues can be strong liars. What proportions do you observe numerically?
  • Using frequency analysis (letters, digrams, trigrams and such), can you (more or less automatically) distinguish, say, different languages or maybe even individual authors. This would be a computational project. The exact focus is up to you.
  • What are the periods of LFSRs and LCGs? When are they maximal? Discuss mathematical results in the spirit of what is hinted at in the lecture notes.
  • When we say that a pseudorandom generator should have good statistical properties, what exactly do we mean? What tests do people apply in practice to evaluate pseudorandom generators?
  • Go into more detail on the prime number theorem. How is it related to the Riemann zeta function and the Riemann hypothesis (this is advanced math)? What goes into its proof? Explore it numerically.
  • Discuss finite fields and their classification. This would be a more mathematical project and should include proving basic results on finite fields.
  • Describe the main ideas involved in finding the first collision found for SHA-1
  • Introduce RSA-OAEP, which is RSA in randomized form with padding.
  • Discuss Frobenius pseudoprimes, which feature in a 1998 primality test by Jon Grantham. You could either include mathematical details, such as proofs, or implement the primality test and experimentally analyze the failure rate.
You are also very welcome to come up with your own ideas for a project. Please talk to me early with your idea, so I can give you a green light.