Lec 1: Class Introduction and Background

Instructor: Jiayu Xu

• Fifth-year assistant professor in EECS, main research interest: public-key cryptography
• xujiay@oregonstate.edu
• Office hours: Wed 3-3:45pm (before class), KEC (Kelley Engineering Center) 2021
• Starting next week

What is this class about??

• Design and cryptanalysis (attack) of block ciphers
• One of the most commonly used cryptographic algorithms in practice
• One of the most active topics in cryptographic research between ~1960 and ~2000

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• This class studies block ciphers from a mostly theoretical perspective
• No implementation; everything pen-and-paper

Comparison with CS 427/529 (“Cryptography”)

Prerequisites

• No course on cryptography required
• YOU MUST BE COMFORTABLE WITH MATH/THEORETICAL CS
• I assume that you know basic stuff about algorithms

Logistics

• 17-20 lectures, attendance expected
• No class on 11/11 (Wed)
• If you cannot/don’t want to attend, tell me in advance
• 3 homework assignments (30%) + 1 presentation (70%)
• Homework: 1-3 problems per assignment
• Read (some paragraphs of) some papers and summarize them
• Work out some specific examples (e.g., how the block cipher works on this particular message)
• You can discuss orally but must write up solutions on your own
• IF YOU USE GENERATIVE AI, INCLUDE THE PROMPTS IN YOUR SOLUTION

Presentation

• Tentative plan:
• Weeks 0-7: My lectures
• Weeks 8-10: Everyone gives a 40-80min presentation
• 1-3 papers not covered in my lectures
• I will provide some sample topics in week 3 or 4
• If no time for this: either (1) 30-40min presentation (so that 2 presentations can be crammed into 1 class), or (2) I talk less and leave more room for your presentations

Reference book

• No textbook
• We will closely follow The Block Cipher Companion by Knudsen and Robshaw (https://link.springer.com/book/10.1007/978-3-642-17342-4)

Setting the Stage

Cryptography

• Cryptography is about communication in the presence of an adversary.
• — Ron Rivest, 1990

Classification of cryptographic algorithms

• 1. By goal
• Confidentiality: adversary cannot gain information about content of communication
• Integrity: adversary cannot manipulate content of communication
• 2. By setting
• Keyless
• Secret key/symmetric: two communicating parties share same secret key
• Public key/asymmetric: two communicating parties use different keys, one public and one secret

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• Block cipher: basic building block for symmetric encryption (secret key setting; aims for confidentiality)
• Can also be used to build hash function/MAC

A brief history

• 1949 — Communication Theory of Secrecy Systems by Shannon
• Foundations for modern cryptography
• Basic ideas behind block cipher design
• Late 1960s to 1977 — design and standardization of Data Encryption Standard (DES)
• 1980 — standardization of DES modes of operation
• 1970s to 1990s — cryptanalysis of DES
• 1990 — differential cryptanalysis
• 1993 — linear cryptanalysis
• 1997 to 2001 — design and standardization of Advanced Encryption Standard (AES)

• 2026 — cryptanalysis powered by AI??

Block cipher research today

• Primary venue for academic publications: Fast Software Encryption (FSE) conference (https://www.iacr.org/meetings/fse)
• Sponsored by the International Association for Cryptologic Research (IACR)
• March every year
• Proceedings: IACR Transactions on Symmetric Cryptology (ToSC) (https://tosc.iacr.org/index.php/ToSC/en)
• Also at general cryptography conferences like CRYPTO, EUROCRYPT, ASIACRYPT