Discrete Mathematics
Hans Georg Schaathun

12th November 2015

Week 3: Cryptography and Modular Arithmetics

Period
2–8 September 2015
Reading
Stein et al cover this material in Chapter 2.
Programme
This document details the programme for the week, including exercises and pointers to other material. It is available in two versions:
  1. as a PDF document.
  2. as a web site. This depends on MathML and may require firefox/iceweasel to display correctly.

The web version includes inline video. The pdf version shows a still image from the video, providing a hyperlink directly to the video on the web site.

Warning!
Stein et al are misleading on page 93 when they say that

In general, any scheme that uses a codebook — a secretly agreed-upon (possibly complicated) code — suffers from these drawbacks.

Firstly, the drawbacks described need not be detrimental. Symmetric ciphers (which seems to be effectively what they mean by a codebook) are still in use with several sound and trust-worthy industry standards available. Secondly, public-key cryptosystems, which is the alternative to symmetric/codebook-based ciphers, share the very same drawbacks.

Extra videos
The videos in this document have been made rather concise, because I believe that the material is better learnt by discussing problems in class, and supplementing with extra exercises in your own time. If you disagree, and think that longer and more elaborate lectures would help you, please consult the «Extra material» tab on the web pages.

1 Wedneday 2 September
2 Thursday 3 September
3 Compulsory Assignment (Tuesday 8 September)

Hans Georg Schaathun / hasc@hials.no