CS 127/CSCI E-127: Introduction to Cryptography
Lecturer: Prof. Salil Vadhan
Shopping week office hours (MD 337): Mon 9/2 2-5, Tue 9/3 11:30-12:30, Thu 9/5 11:30-12:30, 1:30-2:30, Fri 9/6 11-12, 3:30-4:30, Mon 9/9 3:30-5:30, Tue 9/10 11:30-12:30
[Sign up for a 15 min slot on door, or by emailing Carol Harlow (firstname.lastname@example.org)]
Admin Assistant: Carol Harlow (MD 343)
Teaching Fellow: Mark Bun (MD 138), and possibly others TBD
Course website: http://people.seas.harvard.edu/~salil/cs127/
Staff e-mail: email@example.com
Past Q evaluations (under previous numbering CS 127/CSCI E-177): Fall 01, Spring 03, Fall 06 (FAS), Fall 06 (DCE)
Time & Place for CS 127 lectures: TuTh 10-11:30, Maxwell Dworkin G-125
Lecture videos will be recorded for CSCI E-127 students (and will be made available to CS 127 students)
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 CS 121 or 124. The main skills that will be assumed from these courses are:
It is also important that you are familiar with basic discrete probability. A few of the homework problems will involve writing small computer programs (in a language of your choice), so basic programming skills will also be needed.
Additional background that will be helpful:
While it is not necessary to have had exposure to all of these topics prior to CS 127, familiarity with none will probably make it quite difficult to keep up.
The course will have weekly problem sets, typically due 5pm on Fridays via electronic submission. You are allowed 6 late days for the semester, of which at most 2 can be used on any individual problem set. (1 late day = 24 hours exactly). In case of an emergency which requires an exception to these rules, please have your resident dean (or research advisor, in the case of graduate students) contact me. We strongly recommend typing your solutions, ideally using LaTeX.
Students are encouraged to discuss the course material and the homework problems with each other in small groups (2-3 people). Discussion of homework problems may include brainstorming and verbally walking through possible solutions, but should not include one person telling the others how to solve the problem. In addition, each person must write up their solutions independently, and these write-ups should not be checked against each other or passed around.
While working on your problem sets, you may not refer to existing solutions, whether from other students, past offerings of this course, materials available on the internet, or elsewhere. All problem sets should include a collaboration statement listing all collaborators and sources of ideas other than the course materials.
We will use two online tools to facilitate discussion and participation in the class.
The first is NB, a collaborative PDF annotation tool where we will post copies of the reading in advance of lecture. Starting with the Thursday 9/5 lecture, you will be expected to do the reading prior to lecture, and provide comments on it using NB by 9pm the night before. Your comments can point out parts of the reading that you found confusing or interesting, questions that came to your mind as you read the text, answers to other students' questions or comments, etc. The comments will enable us to focus class time on the most difficult and/or interesting aspects of the material.
We will also use Piazza to facilitate additional discussion among students and the staff, beyond those that relate to specific readings.
You will receive invitation emails to both NB and Piazza during the first week of classes (based on the email address you provide in the survey); let us know ASAP if you do not have access.
The required text for the course is: Jonathan Katz and Yehuda Lindell. An Introduction to Modern Cryptography. The authors have are also providing us with a draft of the 2nd edition of the text, which we will use for posting on NB.
Another text that may be useful is Oded Goldreich's Foundations of Cryptography. This two-volume set is a very comprehensive and definitive treatment of the theoretical foundations of cryptography. Volumes I and II cover most of what we'll be doing in this course far greater depth, though the treatment is more abstract than ours. If you plan to continue on in cryptography (particularly as a researcher), I highly recommend purchasing these books.
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, we recommend:
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.