Math 5248: Cryptology and Number Theory
Spring 2020: Professor Andrew Odlyzko
Classes: MW 1:00  2:15, Vincent 113
Office Vincent Hall 511
 phone 6126255413
 email: odlyzko@umn.edu (preferred and most reliable method)
Office hours (starting Mon Jan 27): Mon 5:30  7:00, Tue 2:00  5:30, and by appointment. However, always check this web page
before coming over, as on some days the hours may be restricted.
Textbook: "Cryptology and Number Theory" by Paul Garrett, available
at Alpha Print in Dinkytown (next to McDonald's), 1407 4th St SE, 6123798535.
Copies from previous years, produced by Alpha Print, are the same, and will work fine. However,
the first edition, printed by a regular publisher, has substantial differences, and
will not suffice.
Additional material:
You might find useful two textbooks that are available freely (and legally) online,
Victor Shoup's "A Computational Introduction to Number Theory and Algebra",
Shoup book, and William Stein's
"Elementary Number Theory: Primes, Congruences, and Secrets",
Stein book.
For background and applications, there are many sources available freely
on the Internet. In addition, there are many books available only in print.
For popular historical accounts of cryptology, highly recommended sources
are Simon Singh, "The Code Book"
and (for much more detail) David Kahn, "The Codebreakers".
For applications of cryptology to computer and network security, Paul van Oorschot's
"Computer Security and the Internet: Tools and Jewels",
van Oorschot book
is available on the Internet, and highly recommended.
Computer algebra systems (very helpful, although not absolutely essential and not required): Maple, Mathematica,
available in Math computer labs, and also (for CSE undergrads) for free downloads at
CSE Labs. Some systems available for free on the Web, such
as Wolfram Alpha, will suffice. A calculator is advisable, even if you use a computer
algebra system, to reduce the tedium of computations (and are allowed on midterms, whereas
those computer algebra systems are not).
Tests: No final, three 75minute inclass midterms on Wed Feb 19, Wed Apr 1, and Mon May 4 (last class day).
Weekly homework assignments (usually, excluding midterm days), due (usually) on Wednesdays, first one (a small
one) due Jan. 29.
Will be posted by the preceding Friday, and will (usually) cover material through the preceding Wednesday.
Always due at the beginning of a class, late homeworks will not be accepted.
If you can't make it to class, you can leave your homework in
my mailbox in Vincent 107, or email it to me (in either typeset or scanned form, PDF preferred).
You may work with others on homework
problems. However, you have to write up your solutions yourself, in your own words, to show you
understand the arguments.
Special challenge problems: There will be occasional challenge problems for extra credit.
No collaborations are permitted on those.

Each of these problems will be worth some number of points towards the
homework score (with fractional credit for partial solutions).
Suppose that the maximal score on all the regular homeworks is x, and you get y points
on those regular homeworks and z on the extra credit ones. Then your final homework score will be
the minimum of x and y+z.
Solutions to homework problems will be available through this site, usually posted the
evening of the day they are due. However, they will not be
live links, but URLs that you will have to paste into your browser to download (to keep
crawlers from downloading and archiving them). These are for your use only, do not put
them up on any web sites, Facebook pages, etc.
Tests will be open book; you may bring books, notes, and calculators, but no smart
phones, iPads, or other communication devices can be used, and you have to do all the work
yourself.
Grades: homework will count for 30%, the three tests for 20%, 25%, and 25%, respectively.
Expected effort: This is a 4credit course, so you are expected to devote 12 hours per week,
on average (including lectures).
Solution files for homeworks and midterms are provided for your personal use only. Do not
distribute them via email or posting anyplace.
Scholastic Conduct: Cheating or other misconduct will not be tolerated. The standard University
policies will be followed.
General remarks:
This course develops the basic ideas of cryptology and related areas
of number theory. Both symmetric and public key cryptosystems will
be introduced, as will random number generators and cryptographic
protocols. The basics of the Bitcoin cryptocurrency and of blockchain
technology will be covered
as an example of the application of the techniques developed in the
course.
Homework assignments and other notes:

Material covered on Wed Jan 22: section 1.2 and parts of sections 1.4  1.6 of Chapter 1.

Due Wed Jan 29:

Textbook exercises 1.2.13, 1.2.17, 1.6.01 (10 pts each) and 1.2.23 (20 pts).

Important note: In 1.2.17, assume that m is positive. (The claimed result is false if m is negative.
It would be a good (ungraded) exercise to find a counterexample to the claim of this problem when m is negative.)

Solutions: file http://www.dtc.umn.edu/~odlyzko/Math5248/sol4820200129.pdf

Material covered the week of Jan 27: rest of Chapter 1, and start on sections 26.1 and 26.2.

Due Wed Feb 5:

Textbook exercises 1.5.06, 1.5.09, 1.6.14, 1.6.17, 26.2.08, 26.2.12, 26.2.26, 26.2.27, 26.2.29, and 26.2.30 (10 pts each).

Solutions: file http://www.dtc.umn.edu/~odlyzko/Math5248/sol4820200205.pdf

Material covered the week of Feb 3: more from Section 26.2, covered lightly
Chapter 8, and most of Chapter 2.

Due Wed Feb 12:

Textbook exercises 1.6.09, 1.6.20, 1.7.14, 1.7.19, 1.7.21, 2.1.12, 2.2.04, 2.2.05, 26.2.28, and 26.2.32 (10 pts each).

Solutions: file http://www.dtc.umn.edu/~odlyzko/Math5248/sol4820200212.pdf

Material covered the week of Feb 10: finished Chapter 2, covered Chapter 4, started
on Chapter 6 (sections 6.1 and 6.4), went lightly over Chapter 5.

Wed Feb 19:

In class midterm. Material to be covered: chapters 1, 2, 4, and sections
6.1, 6.4, 26.2, and 26.3.

Open book; you may bring books, notes, and calculators, but no smart phones, iPads, or other communication devices can be used, and you have to do all the work yourself. Blue books will be available, but you do not have to use them.

No homework due this week. For practice on material that was not covered on homeworks,
work out textbook exercises 4.1.05, 4.1.08, 4.2.06,
4.5.01, 4.5.02 (although those two are poorly written, in 4.5.01
all the phrases about probabilities should be deleted, and they should instead be moved to 4.5.02),
6.1.02, and 6.4.01.

Solutions: file http://www.dtc.umn.edu/~odlyzko/Math5248/sol4820200216.pdf

Midterm: file http://www.dtc.umn.edu/~odlyzko/Math5248/exam4820200219.pdf

Midterm solutions: file http://www.dtc.umn.edu/~odlyzko/Math5248/sol4820200219.pdf

Material to be covered on Mon Feb 17: rest of Chapter 6 (sections 6.2 and 6.3), start on chapters 9 and 10
(in a mixedup order).

Due Wed Feb 26:

Textbook exercises 6.2.07, 6.2.08, 6.3.06, 6.3.08, 26.2.25, and 26.2.31 (10 pts each).
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