Lecture 11: April 22, 2026

Reading: text, §10.3–10.4
Assignments: Homework 2, due April 24, 2026

1. Greetings and felicitations!

2. RSA
   1. Provides both authenticity and confidentiality
   2. Based on difficulty of computing totient, φ(n), when n is difficult to factor

3. El Gamal
   1. Provides confidentiality; there is a corresponding algorithm for authenticity
   2. Based on discrete log problem

4. Elliptic curve cryptography
   1. Works for any cryptosystem depending on discrete log problem
   2. Example: Elliptic curve El Gamal
   3. Selection of curves

5. Cryptographic Checksums
   1. Function y = h(x): easy to compute y given x; computationally infeasible to compute x given y
   2. Variant: given x and y, computationally infeasible to find a second x′ such that y = h(x′)
   3. Keyed vs. keyless

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 153A, Computer & Information Security & Privacy I Version of April 22, 2026 at 1:54M

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