block chain

linked list with hash pointers = “block chain”

Cryptocurrencies
CreateCoin[ uniqueCoinID ]
signed by pk (scret signing key)
-> Goofy coin

A coin’s owner can spend it – using cryptographic operations

signed by pk
Pay to pkalice:()

signed by pk
CreateCoin[ uniqueCoinID ]

Scrooge coin
A designated entity publishes an append-only ledger containing the history of all the transactions that have happened.
All transactions be written to the ledger before they are accepted.