Bitcoin was started on October 31, 2008. Open-sourced Jan 3, 2009. Creator pseudonym Satoshi Nakamoto. Technically not first cryptocurrency, DigiCash came in 1990. First decentralized virtual currency.

Medium of exchange: portable, durable, fungible Unit of account: divisible, fungible Store of value: durable, scarce, fungible Durable Portable Divisible Fungible Scarce

Used on most continents, still a legal currency in Papua New Guinea alongside their paper money.

Stone money was made in Micronesia and Guam, transported to the island of Yap as currency. Value from the story of how hard it was to transport. Ownership transferred by oral history, stones not moved.

Pretty popular. Still used today.

Used to be a currency form of gold and silver, after World War 1 pretty much everybody decided to switch to unbacked "floating money" so they could fuel government expenses with inflation.

If I send you a file, I still have the file. Digital items can be duplicated; how can I send you something the way I do in the physical world? The Yapanese people had the right idea: use a ledger.

We can use a ledger to keep track of how much money each person has. If I want to send money, we reduce my account and increase someone else's account. This is similar to how Paypal works at a simple level. Problems: Everyone has to trust whoever maintains the ledger, since they can monitor it and change it.

We can use public and private keys to control balances in an anonymous ledger.

Then instead of sending a payment from "Joshua" to "Jack", it's a payment from "private keys A and B" to "public key C".

There's a company that actually did this, called DigiCash. they maintained a ledger with cryptographically controlled balances. Consumers weren't concerned enough about security or privacy and they ran out of money.

payment information usernames DNS

embedding a hash in the blockchain demonstrates an item's existence at point in the past

DAO Ethereum/RootStock