Bitcoin is a cryptocurrency, a digital asset designed to work as a medium of exchange that uses cryptography to control its creation and management, rather than relying on central authorities. The presumed pseudonymous Satoshi Nakamoto integrated many existing ideas from the cypherpunk community when creating bitcoin. Over the course of bitcoin's history, it has undergone rapid growth to become a significant currency both on and offline – from the mid 2010s, some businesses began accepting bitcoin in addition to traditional currencies.
Researchers have pointed out at a "trend towards centralization". Although bitcoin can be sent directly to the bitcoin network, in practice intermediaries are widely used.:220–222 Bitcoin miners join large mining pools to minimize the variance of their income.:215, 219–222:3 Because transactions on the network are confirmed by miners, decentralization of the network requires that no single miner or mining pool obtains 51% of the hashing power, which would allow them to double-spend coins, prevent certain transactions from being verified and prevent other miners from earning income. As of 2013 just six mining pools controlled 75% of overall bitcoin hashing power. In 2014 mining pool Ghash.io obtained 51% hashing power which raised significant controversies about the safety of the network. The pool has voluntarily capped their hashing power at 39.99% and requested other pools to act responsibly for the benefit of the whole network.
The most recent exciting news in Bitcoin history began in November 2017 and led to the current all-time high for the cryptocurrency. In 2017, Bitcoin went from trading at just over $900 to about $20,000. This was a journey with many ups and downs along the way, a drop in trading volumes due to the People’s Bank of China tightening oversight of Bitcoin exchanges and the U.S. Securities and Exchange Commission rejecting a Bitcoin exchange-traded fund.
More recently, at a congressional hearing on Capitol Hill, global economist and New York University professor Nouriel Roubini said, "Crypto is the mother or father of all scams and bubbles." He called out "swindlers" who tapped into investors' fear of missing out and took them for a ride with "crappy assets that went into a bust and crash — in a matter of months — like you have not seen in any history of financial bubbles."
Bitcoin is pseudonymous, meaning that funds are not tied to real-world entities but rather bitcoin addresses. Owners of bitcoin addresses are not explicitly identified, but all transactions on the blockchain are public. In addition, transactions can be linked to individuals and companies through "idioms of use" (e.g., transactions that spend coins from multiple inputs indicate that the inputs may have a common owner) and corroborating public transaction data with known information on owners of certain addresses. Additionally, bitcoin exchanges, where bitcoins are traded for traditional currencies, may be required by law to collect personal information.