1. DTTF/NB479: Dszquphsbqiz Day 33
Announcements:
Today: digital cash
Tomorrow: quiz on ch. 6-9
8 questions
Thursday: presentations
Elliptic curves
MD5 vulnerabilities
Friday: workday for presentations.
Anyone needing help can meet me in my office.
Questions?

2. One last (set of) Schneier joke(s)

3. Digital Cash: goals Electronic: want speed and security
Can’t be counterfeited
Anonymous: spender’s ID not disclosed to merchant
Payment done offline
Transferable
Divisible (can make change)
Okimoto and Ohta: Universal electronic cash, In Proc. Advances in Computing – CRYPTO, 1991

4. Digital Cash Exercise
T&W 11.1 summarizes a system satisfying goals 1-4 (can’t give coins away, a single denomination only)
Focus is on preventing fraud due to double-spending
Adds lots of complexity
Interpret this as “adds lots of equations”
Handout
Read/skim the 3-page summary of chapter.
Do the questions alone or with a partner.