Resumo:
The amount of computational power devoted to anonymous, decentralized blockchains
such as Bitcoin’s must simultaneously satisfy two conditions in equilibrium: (1) a zero-profit
condition among miners, who engage in a rent-seeking competition for the prize associated
with adding the next block to the chain; and (2) an incentive compatibility condition on the
system’s vulnerability to a “majority attack”, namely that the computational costs of such an
attack must exceed the benefits. Together, these two equations imply that (3) the recurring,
“flow”, payments to miners for running the blockchain must be large relative to the one-off,
“stock”, benefits of attacking it. This is very expensive! The constraint is softer (i.e., stock
versus stock) if both (i) the mining technology used to run the blockchain is both scarce and
non-repurposable, and (ii) any majority attack is a “sabotage” in that it causes a collapse in
the economic value of the blockchain; however, reliance on non-repurposable technology for
security and vulnerability to sabotage each raise their own concerns, and point to specific
collapse scenarios. In particular, the model suggests that Bitcoin would be majority attacked
if it became sufficiently economically important — e.g., if it became a “store of value” akin to
gold — which suggests that there are intrinsic economic limits to how economically important
it can become in the first place.
The Economic Limits of Bitcoin and the BlockchainEric BudishNBER Working Paper No. 24717June 2018