Outline for March 8, 2006

Reading: text, §12.2–12.5

1. Greetings and felicitations!
   1. Puzzle of the day
2. Attacks
   1. Exhaustive search: password is 1-8 chars, say 96 possibles; it's about 7×10¹⁶
   2. Inspired guessing: think of what people would like (see above)
   3. Random guessing: can’t defend against it; bad login messages aid it
   4. Scavenging: passwords often typed where they might be recorded as login name, in other contexts, etc.
   5. Ask the user: very common with some public access services
3. Password aging
   1. Pick age so when password is guessed, it’s no longer valid
   2. Implementation: track previous passwords vs. upper, lower time bounds
4. Ultimate in aging: 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
5. 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 on wire or network
6. Biometrics
   1. Depend on physical characteristics
   2. Examples: pattern of typing (remarkably effective), retinal scans, etc.
7. Location
   1. Bind user to some location detection device (human, GPS)
   2. Authenticate by location of the device