Prior to the release of bitcoin there were a number of digital cash technologies starting with the issuer based ecash protocols of David Chaum and Stefan Brands. Adam Back developed hashcash, a proof-of-work scheme for spam control. The first proposals for distributed digital scarcity based cryptocurrencies were Wei Dai's b-money and Nick Szabo's bit gold. Hal Finney developed reusable proof of work (RPOW) using hashcash as its proof of work algorithm.
To be accepted by the rest of the network, a new block must contain a so-called proof-of-work (PoW). The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash. The PoW requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.:ch. 8 This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is the ascending natural numbers: 0, 1, 2, 3, ...:ch. 8) before meeting the difficulty target.
Nigel Dodd argues in The Social Life of Bitcoin that the essence of the bitcoin ideology is to remove money from social, as well as governmental, control. Dodd quotes a YouTube video, with Roger Ver, Jeff Berwick, Charlie Shrem, Andreas Antonopoulos, Gavin Wood, Trace Meyer and other proponents of bitcoin reading The Declaration of Bitcoin's Independence. The declaration includes a message of crypto-anarchism with the words: "Bitcoin is inherently anti-establishment, anti-system, and anti-state. Bitcoin undermines governments and disrupts institutions because bitcoin is fundamentally humanitarian."
In early February 2014, one of the largest bitcoin exchanges, Mt. Gox, suspended withdrawals citing technical issues. By the end of the month, Mt. Gox had filed for bankruptcy protection in Japan amid reports that 744,000 bitcoins had been stolen. Months before the filing, the popularity of Mt. Gox had waned as users experienced difficulties withdrawing funds.
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