CS 255: Introduction to Cryptography

Winter 2026

Optional readings can be found in the textbooks denoted by KL and AC in the syllabus below. The optional AC book, by Boneh and Shoup, is more advanced (and free) and is intended for students wishing to go deeper. The online version of the course is another resource for the material covered in class.

Course syllabus

Lecture 1:
Mon 1/5/26
Overview of cryptography. What is a cipher?
Readings: AC ch.2;   KL ch 2.
Basic symmetric-key encryption
Lecture 2:
Wed 1/7/26
One time pad and stream ciphers
Perfect secrecy and the one time pad;
semantic security and stream ciphers.
Readings: AC ch.3;   KL 3.2.1-3.4.2.
Lecture 3:
Mon 1/12/26
Block ciphers
Iterated Even-Mansour ciphers and the AES block cipher.
Readings: AC ch. 4.1, 4.2;   KL ch 6.1-6.2.
Lecture 4:
Wed 1/14/26
How to use a block cipher   [pdf, pptx]
Pseudo Random Permutations (PRP); Pseudo Random Functions (PRF);
semantic security, and basic modes of operation
Readings: AC. ch. 4.4, 5;   KL ch 3.5
Holiday:
Mon 1/19/26
MLK: no classes
Lecture 5:
Wed 1/21/26
CPA Security plus attacks on block ciphers   [pdf, pptx]
Nonce-based encryption, CBC and randomized counter mode,
differential & linear cryptanalysis, side channels, and quantum attacks.
Readings: AC ch. 4.3;   KL ch 3.4.2,3.6
Message integrity
Lecture 6:
Mon 1/26/26
Message integrity: definition and applications
CBC-MAC and PMAC.
Readings: AC ch. 6;   KL ch 4.1-4.3
Lecture 7:
Wed 1/28/26
Collision resistant hashing
Merkle-Damgard and Davies-Meyer; MACs from collision resistance;
case studies: SHA and HMAC.
Readings: AC ch. 8.1-8.9;   KL ch 5.1-5.3
Lecture 8:
Mon 2/2/26
Authenticated encryption: security against active attacks
Properties and secure constructions
Readings: AC ch. 9;   KL ch 4.5
Public key cryptography
Lecture 9:
Wed 2/4/26
Arithmetic modulo primes and finite cyclic groups
Readings: KL ch 8.
Summary of relevant facts: pdf.
Lecture 10:
Mon 2/9/26
Cryptography using finite cyclic groups
anonymous key exchange (Diffie-Hellman); the CDH and discrete-log assumptions
Readings: AC ch. 10;   KL ch 9, 11.4.1
Lecture 11:
Wed 2/11/26
ElGamal public key encryption
semantically secure ElGamal encryption; CCA security
Readings: AC ch. 11;   KL ch 9, 11.4.1
Holiday:
Mon 2/16/26
President's day: no classes.
Lecture 12:
Wed 2/18/26
Public key encryption using a trapdoor function   [pdf, pptx]
The RSA trapdoor permutation and its applications
Readings: AC ch. 10.2, 10.3;   KL ch 11.5
Summary of relevant facts: pdf.
Digital signatures
Lecture 13:
Mon 2/23/26
Digital signatures: definitions and applications
How to sign using RSA.
Readings: AC ch. 13;   KL ch 12.1-12.4
Lecture 14:
Wed 2/25/26
More signature schemes and applications   [pdf]
hash based signatures;
certificates, certificate transparency, certificate revocation.
Readings: AC ch. 13.8, ch. 14;   KL ch 12.5-12.8
Protocols
Lecture 15:
Mon 3/2/26
Identification protocols   [pdf, pptx]
password protocols, salts; one time passwords (S/Key and SecurID);
challenge response authentication.
Readings: AC ch. 18;
Lecture 16:
Wed 3/4/26
Authenticated key exchange and SSL/TLS session setup   [pdf, pptx]
Readings: AC ch. 21;
Lecture 17:
Mon 3/9/26
Post-quantum Cryptography
Readings: The quantum menace and Post-quantum signatures
Lecture 18:
Wed 3/11/26
Intro to zero-knowledge proofs and their applications
Readings: AC ch. 20;