1. Announcements: 1. Today: digital cash 2. Thursday will be workday for presentations. Anyone needing help can meet me in my office. Friday: presentations Friday: presentations Elliptic curves Quantum cryptography Questions? DTTF/NB479: DszquphsbqizDay 34

2. 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

3. Digital Cash Exercise T&W 11.1 summarizes a system statsfying goals 1-4 (can’t give coins away, a single denomination only) Focus is on preventing fraud due to double-spending Focus is on preventing fraud due to double-spending Adds lots of complexity Adds lots of complexity Interpret this as “adds lots of equations” Interpret this as “adds lots of equations”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. Submit at end of class Submit at end of class