Announcements:Announcements:1.1. Today: digital cashToday: digital cash

2.2. Tomorrow: quiz on ch. 6-9Tomorrow: quiz on ch. 6-91.1. 8 questions8 questions

3.3. Thursday: presentationsThursday: presentationsElliptic curvesElliptic curves

MD5 vulnerabilitiesMD5 vulnerabilities

4.4. Friday: workday for presentations. Friday: workday for presentations. 1.1. Anyone needing help can meet me in my office.Anyone needing help can meet me in my office.

Questions? Questions?

DTTF/NB479: DszquphsbqizDTTF/NB479: Dszquphsbqiz Day 33Day 33

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

http://geekz.co.uk/schneierfacts/ http://geekz.co.uk/schneierfacts/

Digital Cash: goalsDigital Cash: goals

Electronic: want speed and securityElectronic: want speed and security

Can’t be counterfeitedCan’t be counterfeited

Anonymous: spender’s ID not disclosed to Anonymous: spender’s ID not disclosed to merchantmerchant

Payment done offlinePayment done offline

TransferableTransferable

Divisible (can make change)Divisible (can make change)

Okimoto and Ohta: Universal electronic cash, In Proc. Advances in Computing – CRYPTO, 1991

Digital Cash ExerciseDigital Cash Exercise

T&W 11.1 summarizes a system satisfying goals 1-4 T&W 11.1 summarizes a system satisfying goals 1-4 (can’t give coins away, a single denomination only)(can’t give coins away, a single denomination only)

Focus is on preventing fraud due to double-spendingFocus is on preventing fraud due to double-spending Adds lots of complexityAdds lots of complexity Interpret this as “adds lots of equations”Interpret this as “adds lots of equations”

Handout Handout Read/skim the 3-page summary of chapter.Read/skim the 3-page summary of chapter. Do the questions alone or with a partner.Do the questions alone or with a partner.