CSE 426: Cryptography (Autumn 2025)

Time and location: MWF 11:30-12:20p, CSE2 G01

Sections:

Section A: Th 1:30-2:20p, JHN 026
Section B: Th 2:30-3:20p, MGH 251

Dicussion platform: We will be using edstem. You should have received an invite, otherwise contact us for assistance.

How to contact us: Use cse426-staff@cs to reach out to the whole staff. Use this for extension requests exceeding your allowed late days, and also for urgent matters that can be shared with the whole staff. For non-urgent issues, we prefer if you ask a private question on edstem. For private matters, please contact the instructor (ST) directly.

General description

Cryptography provides tools for ensuring the confidentiality and integrity of sensitive digital data. This course covers the design and application of cryptographic objects such as encryption, message authentication, and digital signatures, as well as advanced cryptographic objects and protocols, such as zero-knowledge proofs, secure multi-party computation, and fully homomorphic encryption. For each cryptographic object, we formalize its security goal, show schemes that achieve the desired security, and study security attacks or security proofs that establish the insecurity or security of the scheme at hand. Through this course, we aim to give an overview of the discipline of cryptography, the proper usage and application of important cryptographic tools, and methodologies that modern cryptography offers for developing cryptographic solutions to natural security problems.

Pre-req: CSE 312. The class will be self-contained. But students are expected to understand mathematical definitions and proofs, and write simple ones. Exposure to basic probability / algebra / number theory. (Contact the instructor if in doubt.)

Important note: CSE 426 vs. CSE 484. Students sometimes enroll in CSE 426 (Cryptography) as a stand-in for CSE 484 (Computer Security), or while waiting for space in CSE 484. This is not always a very good idea, unless you are certain that CSE 426 is a good match. CSE 484 includes some cryptography but focuses broadly on security and requires less math, whereas CSE 426 dives much deeper into cryptography and demands a higher level of mathematical maturity. If your primary goal is to study computer security, and especially if you struggled in CSE 311/312, CSE 426 is not a good substitute.

Policies

Accommodations: We will follow UW policies for disability accommodations and religious accommodations.

Academic conduct: Please also refer to UW policies on student conduct and academic integrity

DRS accommodations: If you want DRS accommodations, you should email DRS as soon as possible. DRS will contact us directly to get these accomodations set up for you. Feel free to reach out to us to ensure we have received it, but only after DRS has been contacted.

Homework policy:

There will be seven homework assignments, to be solved individually. Solutions are to be submitted over Gradescope.
Homeworks are posted on Wednesday night, by midnight, and due one week later, with the exception of Homework 7, which is due two weeks later.
We strongly encourage you to type solutions up using LaTeX. Alternatively, you can use any other tool that properly displays equations (e.g., Word's equation editor).
You must show your work; at a minimum 1-2 sentences per question, but ideally as much as you would need to explain to a fellow classmate who had not solved the problem before. Be concise. A correct answer with no work is worth nothing, less than a wrong answer with sufficient explanations explaining your reasoning.
It is okay to discuss with other students in coming up with the homework solutions, but you must list all your collaborators at the top of each homework. Moreover, you have to write up your own solution and be able to explain your answer if asked to do so. If there are any doubts, we plan to do some spot checks in which we ask students to explain one of their solutions (or solve a slight variant of the problem they solved on the homework) in person.
You have a total of seven late days during the quarter, but you can only use up to three late days on any one assignment. This will allow us to post solutions in a timely manner prior to the submission deadline for the next assignment. Please plan ahead, as we will not be willing to add any additional late days except in absolute, verifiable emergencies. Sticking to the schedule is also important for you to remain on track as the class progresses, and thus use late days sparingly.
Regrade requests are to be submitted within one week of the graded homework assignment being released.

Exams policy: All exams (midterm and final) will take place in the classroom. The final exam will be cumulative. The exams will be closed book, but you will be allowed to use a cheatsheet (more information will be provided at due time).

Final grade: The final grade will be computed as follows: Homework (45%); Midterm (20%); Final (35%)

Policy on Generative AI: You may not use Generative AI tools to solve course tasks. If you use such tools for other purposes—for example, improving the clarity of your writing or polishing the presentation of your solution—you must clearly disclose this. Your disclosure should specify which model you used and include the prompts you used. Be warned: the quality of cryptography solutions produced by current models is poor, and attempts to use them are usually easy to detect. This policy is in place because the goal of CSE 426 is for you to develop a deep understanding of cryptography through your own reasoning and problem-solving. Outsourcing that process undermines your learning and defeats the purpose of the course. We plan to show you some examples of incorrect Gen AI output.