Nifty little tool showing the estimated cost of controlling the majority of the Bitcoin network:
https://www.resallex.com/bitcoin/brix Would love to see something similar for the Tor network - my guess is that the cost there is probably at least an order-of-magnitude lower, but that's just my intuition. R >From the site.. > Introduction > > *Equilibrium 51% Attack Cost:* This is a metric attempting to calculate > the total present value cost required to attack the Bitcoin network through > majority hashing power (51% attack). The metric is meant to be viewed as a > snapshot in time as if an attacker decided to invest in attacking the > network under the current conditions. > *BRIX Score:* "Bitcoin Robustness Index" - The relative rank of Bitcoin's > 51% attack cost compared to annual military expenditures among all nations. > Method This metric is, in essence, equal to 51% of the present value > ("PV") of all future revenues derived from bitcoin mining using current Mt. > Gox prices. Revenues include both block rewards and transaction fees. The > purpose behind using PV as a measuring tool is to approximate the > incentives to miners to build upon the Bitcoin network. The measure can be > viewed as an aggregate of all the cost-benefit analyses done by individual > miners. We believe this is superior to other methods of calculating the > attack cost, including variables such as current hash rates and current > capital costs, because the model is independent of technology advancements. > Under the equilibrium model, miners will continue to invest in equipment > until they reach the point where marginal cost equals marginal revenue (the > point of profit maximization). Under perfect competition (of which bitcoin > mining is effectively), this point will also be where aggregate cost equals > aggregate revenue. If we assume the variables that can affect mining > revenue are held constant ($/btc & transaction fees), then it is easy to > calculate aggregate revenue and therefore also aggregate cost. Since we > know aggregate revenue equals aggregate cost, by calculating 51% of > aggregate revenue we effectively calculate 51% of the aggregate cost to > miners. > > > We calculated this metric by discounting each block reward (210,000 > blocks) as if it were an annuity and then discounting it further to its > present value. Then, we added estimated transaction fees based off > historical records. > Assumptions > > This metric is meant to represent a model at equilibrium. Therefore it > represents a snapshot of 51% of the incentive to miners at the current > price and current transaction fee levels. The idea is that miners are > willing to invest in the network as long as it is profitable to continue > doing so. We assume the following: > > - * Rational Actors: * We assume all mining participants are rational > actors and strictly pursue profit maximization. We ignore all other > motivations, including political, emotional, and reputational. All other > heuristics and biases are ignored. > - * Static Variables: * We assume that the variables in the model are > static, and therefore represent a 'snapshot in time'. There are no growth > forecasts for either price or transaction fees. > - * Perfect Competition: * We assume that all miners and potential > attackers have access to the same technology, resources, and information. > There is no technological advantage for any party that would exclusively > decrease mining costs or otherwise acquire mining equipment faster. > - * Discount Rate: 8% * Our model discounts future cash flows by 8%. > >
