The Bank for International Settlement (BIS) published a paper focusing on how Bitcoin and related cryptocurrencies verify that payments are final, that is, irreversible once written into the blockchain. It points to the high costs of achieving such finality via “proof-of-work”. It then weighs the outlook for cryptocurrencies based on this kind of algorithm, and looks at possible future avenues for progress.
The paper shows that two economic limitations affect the outlook of cryptocurrencies modelled on proof-of-work. The first lies in the extreme costs of ensuring payment finality in a reasonable space of time. The second is that these systems will not be able to generate transaction fees that are adequate to guarantee payment security in future. The paper shows that the future of Bitcoin and related cryptocurrencies is crucially affected by the interplay of these two limitations.
After surveying the market for transactions and the way fees are determined, the paper finds that the liquidity of cryptocurrencies is set to shrink. In this light, the paper then asks how technical progress might raise the efficiency of Bitcoin-type payments. So-called second-layer solutions such as the Lightning Network could help. Or methods other than proof-of-work could be used to achieve payment finality. But these might require coordination mechanisms, implying support from a central institution. Thus, the current technology seems unlikely to replace the current monetary and financial infrastructure. Instead, the question is rather how the technology might complement existing arrangements.
The paper discusses the economics of how Bitcoin achieves data immutability, and thus payment finality, via costly computations, ie “proof-of-work”. Further, it explores what the future might hold for cryptocurrencies modelled on this type of consensus algorithm. The conclusions are, first, that Bitcoin counterfeiting via “double-spending” attacks is inherently profitable, making payment finality based on proof-of-work extremely expensive. Second, the transaction market cannot generate an adequate level of “mining” income via fees as users free-ride on the fees of other transactions in a block and in the subsequent blockchain. Instead, newly minted bitcoins, known as block rewards, have made up the bulk of mining income to date. Looking ahead, these two limitations imply that liquidity is set to fall dramatically as these block rewards are phased out. Simple calculations suggest that once block rewards are zero, it could take months before a Bitcoin payment is final, unless new technologies are deployed to speed up payment finality. Second-layer solutions such as the Lightning Network might help, but the only fundamental remedy would be to depart from proof-of-work, which would probably require some form of social coordination or institutionalisation.