CSCI E-177: Introduction to Cryptography
Lecturer: Prof. Salil Vadhan
and Dr. Alon Rosen
Teaching Assistant: Christopher Thorpe
Course website: http://www.people.seas.harvard.edu/~salil/cs120
Staff e-mail: firstname.lastname@example.org
Past FAS CUE evalutions: Fall 01, Spring 03
Cryptography is the science of designing algorithms and protocols that guarantee privacy, authenticity, and integrity of data when parties are communicating or computing in an insecure environment. The recent explosion of electronic communication and commerce has expanded the significance of cryptography far beyond its historical military role into all of our daily lives. For example, cryptography provides the technology that allows you to use your credit card to make on-line purchases without allowing other people on the internet to learn your credit card number.
The past 25 years have also seen cryptography transformed from an ad hoc collection of mysterious tricks into a rigorous science based on firm complexity-theoretic foundations. It is this modern, complexity-theoretic approach to cryptography that will be the focus of this course. Specifically, we will see how cryptographic problems can be given precise mathematical definitions. Then we will construct algorithms which provably satisfy these definitions, under precisely stated and widely believed assumptions. For example, we will see how to prove statements of the flavor "Encryption algorithm X hides all information about the message being transmitted, under the assumption that factoring integers is computationally infeasible." (Of course, this kind of statement will be given a precise meaning.)
What can you hope to learn from this course?
What this course will NOT teach you:
The formal prerequisite for the course is one prior course in theoretical computer science, such as CSCI E-207 or E-124. (Students with strong math backgrounds may be able to manage with extra background reading and/or taking E-124 concurrently; come to my office hours to discuss.) The main skills that will be assumed from these courses are:
It is also important that you are familiar with basic probability . Additional background that will be helpful:
While it is not necessary to have had exposure to all
of these topics prior to CSCI E-177, familiarity with none will probably make it
quite difficult to keep up.
Your class participation grade is based on
participation in sections, but can also be boosted by participation in section,
emailing the course staff,
and/or coming to office hours or section with "good" questions or
comments. A "good" question is one which is not just aimed to help you
answer questions on the problem set or exam. It is one that shows genuine
interest in the material and that you have been thinking about the course
material on your own. Do not be afraid of asking "stupid" questions!
Class participation also includes viewing the online lectures,
participating in sections either in person or online, and
participating in discussions on the course website. We will account for
the different nature of class participation for distance students when
computing their class participation grades.
The course will have weekly problem sets, due as posted on each assignment and the course website. They will be due either in the course box marked CS120 in the basement of Maxwell Dworkin or electronically by submission to the Assignments dropbox on the course website. If you prefer to handwrite your assignments, you may scan them and submit them electronically instead of submitting them in the course box. Please remember to write your name on the assignment and indicate it is for CSCI E-177.
Assignments are due on the date specified on the assignment. It is important that students keep up with the lecture material by completing the assignments on time; in addition, we cannot return graded assignments or solutions until all students have handed in their assignments. Late work will only be accepted in case of exceptional unforeseen circumstances by prior application to the teaching assistant: if something comes up that may prevent you from turning your work in on time, ask for more time immediately, not when you run out of time the day before the assignment is due. Project deadlines at work and obligations for other courses are not exceptional, and you should budget your time accordingly.
Collaboration on homework is permitted with small groups of other students, provided that you limit your collaboration to verbal discussion of solutions in general terms and not specific language of the solutions to be handed in. Because email tends to result in specific, crafted language, students are expressly forbidden from exchanging email about solutions to problem sets. You may collaborate via in-person meetings, telephone, instant messenger, or web conference; please clearly indicate the names of any collaborators on your assignment.
There will be weekly sections, which will be used to clarify difficult points from lecture, review background material, go over previous homework solutions, and sometimes provide interesting supplementary material. We will attempt to schedule sections at a time when distance students can participate over online chat. Section times will be arranged in the first week or two of class.
There is no required text for the course other than the lecture notes, but you may find the following to be useful references (but beware that some of the notation, conventions, and definitions may differ slightly from lecture):
Other texts on cryptography take a much less careful approach to definitions and proofs of security than we do. Still, they can serve as good references for more examples of concrete cryptosystems used in practice and some high-level ideas. After this course, you should understand how to critically evaluate the merits or deficiencies of the cryptosystems described in the books below (and indeed we urge you to have a critical eye when reading them):
For background reading on probability, algorithms, complexity theory, and number theory, I recommend: