Data Storage/Key Locations

Each of the three principals knows the following (is stored in local memory):

Smart Card:

• K_sc : unique shared key between this one smartcard and the bank.
• K_m : shared key between all soda machines and smartcards (and the bank)
• ID_sc : unique identifier for this smart card, stored in cleartext.
• {ID_sc}K^a_sm : same unique identifier, encrypted with a key known to all soda machines and the bank.
• Balance : cleartext balance, also referred to as B1 elsewhere.
• {Balance}K^a_sm : balance encrypted with a key known to all soda machines and the bank.
• Transaction Log, each entry contains the following fields:
  • ID_sm : unique identifier of the soda machine.
  • {ID_sm}K_sm : unique identifier encrypted with a unique key known only to the machine and bank
  • Amount : self-explanatory. Cleartext amount of transaction.
  • {Amount}K_sm : amount encryted so that only the issuing soda machine and bank can read it.

Soda Machine:

• K_sm : unique shared key between this one soda machine and the bank.
• K_m : shared key between all soda machines and smartcards (and the bank)
• ID_sm : unique identifier for this soda machine, stored in cleartext.
• {ID_sm}K^a_sc : same unique identifier, encrypted with a key known to all smart cards and the bank.
• Transaction Log, each entry contains the following fields:
  • ID_sc : unique identifier of the smart card.
  • {ID_sc}K_sc : unique identifier encrypted with a unique key known only to the smart card and bank
  • Amount : self-explanatory. Cleartext amount of transaction.
  • {Amount}K_sc : amount encryted so that only the issuing smart card and bank can read it

Bank:

• All K_sc
• All K_sm
• K_m
• K^a_sc
• K^a_sm
• All ID_sc, and complete past transaction logs for each ID_sc
• All past smartcard balances, and current balance
• All ID_sm, and complete past transaction logs for each ID_sm