Outline for October 29, 2025

Reading: text, §13.5–13.9, 18.1
Assignments: Homework 3, due November 5; Project selection, due November 7

1. Greetings and Felicitations!

2. Defenses
   1. For trial and error at login: dropping or back-off

3. Challenge-response systems
   1. Computer issues challenge, user presents response to verify secret information known/item possessed
   2. Example operations: f(x) = x+1, random, string (for users without computers), time of day, computer sends E(x), you answer E(D(E(x))+1)
   3. Note: password never sent over network

4. One-Time Password
   1. Password is valid for only one use
   2. May work from list, or new password may be generated from old by a function or a hardware token

5. Biometrics
   1. Depend on physical characteristics
   2. Examples: pattern of typing (remarkably effective), retinal scans, etc.

6. Location
   1. Bind user to some location detection device (human, GPS)
   2. Authenticate by location of the device

7. Multi-factor authentication

8. Confinement problem
   1. Total isolation
   2. Isolation

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

ECS 235A, Computer and Information Security Version of October 27, 2025 at 10:54AM

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