Bitcoin has "severe" economic limitations as a means of payment. That's according to a new working paper (PDF) from the Bank of International Settlements (BIS), the so-called central bank for central banks. Two limitations stem from the method, called proof-of-work, that Bitcoin and many other blockchain networks use to secure their distributed ledgers.
First, as we saw recently in an attack on Ethereum Classic, if someone is able to gain more than half of the mining capacity of a proof-of-work system, they can use it reverse transactions and effectively spend the same bitcoins twice. Called a double-spend attack, the attacker can pull this off by paying them in cryptocurrency before creating an alternative version of the blockchain in which the payment never happens. The deeper a transaction is in the blockchain, the more computing power is needed to create an alternative chain that doesn't contain that transaction, and the lower the probability that a double spend attack will occur. That's why merchants who accept Bitcoin as payment must wait for several additional sets of transactions, or blocks, to be added to the chain after the one containing the payment before they release the purchased goods.
But a transaction isn't truly final, argues Raphael Auer, a BIS economist, until it is so deep in the blockchain that it is in fact impossible for a double-spend attacker to profit. Achieving this, which he calls "economic payment finality," is extremely expensive to the network.
The second economic limitation pertains to the way the network pays miners to keep it secure. In Bitcoin, a miner who adds a new block to the chain earns a set number of bitcoins, called the "block reward." They can also earn transaction fees, which individual Bitcoin users propose when they submit new transactions. This income is incentive for miners to act in the interest of the whole network instead of selfishly attempting double-spend attacks. In Bitcoin, however, this will shrink over time, because the system is designed to phase out the block reward. Transaction fees alone won't be enough to keep the security of the system from deteriorating once this happens, says Auer, meaning that achieving true payment finality will take longer and longer. When the reward reaches zero, it might even take months for a payment to become irreversible, he writes, concluding: "The only fundamental remedy would be to depart from proof-of-work." (See also: "Bitcoin's inherent economics could keep it from every being very important")
Auer notes that making such a substantial change to a cryptocurrency network's software "would probably require some form of social coordination or institutionalization." Bitcoin has historically struggled with infighting and gridlock over technical decisions, however. Meanwhile, Ethereum is trying to switch from proof-of-work to an alternative method called proof-of-stake, and its community is realizing how difficult this is from a social perspective.
Will people ditch cash for cryptocurrency? Japan is about to find out. Most payments in the world's third largest economy are still made in cash, but with the 2020 Olympics approaching, the government is pressing for more cashless payment options. Several of Japan's biggest banks are now betting that blockchain technology will be the key to getting people to ditch their banknotes. Sure, Japan's retail investors already love crypto, and the government is very well versed in the technology thanks to the hard lessons of Mt. Gox, which collapsed in 2014 after losing half a billion dollars worth of its users' cryptocurrency. But it will only work if Japan's banks are able to do something that hasn't yet been done: make cryptocurrency payments easy and useful. For the whole story, check out my new feature.
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