While showing great promise, Bitcoin requires users to wait tens of minutes for transactions to commit – even then offering only probabilistic guarantees. This paper introduces ByzCoin, a novel Byzantine consensus protocol that leverages scalable collective signing to commit Bitcoin transactions irreversibly within seconds. ByzCoin achieves Byzantine consensus while preserving Bitcoin’s open me...

Bitcoin is a popular digital currency for online payments, realized as a decentralized peer-to-peer electronic cash system. Bitcoin keeps a ledger of all transactions; the majority of the participants decides on the correct ledger. Since there is no trusted third party to guard against double spending, and inspired by its popularity, we would like to investigate the correctness of the Bitcoin p...

This paper presents an extension to Bitcoin’s script language enabling covenants, a primitive that allows transactions to restrict how the value they transfer is used in the future. Covenants expand the set of financial instruments expressible in Bitcoin, and enable new powerful and novel use cases. We illustrate two novel security constructs built using covenants. The first, vaults, focuses on...

We present and validate a novel mathematical model of the blockchain mining process and use it to conduct an economic evaluation of the double-spend attack, which is fundamental to all blockchain systems. Our analysis focuses on the value of transactions that can be secured under a conventional double-spend attack, both with and without a concurrent eclipse attack. We account for an attacker ca...

Humanity has almost won its battle with many infectious diseases, thus increasing longevity, but is now confronted with challenges arising from population aging (1). A blessing turned into a curse as modern societies began struggling with prosperity diseases proliferation (2). Such obstacles are notable in the largest Western Balkan country (1). One-fifth of the Serbian population is aged 65, w...

BACKGROUND Research has documented dramatic variation in health care spending across the United States that has little relationship to health outcomes. Although high-spending areas have more physicians per capita, it is not known whether this disparity fully explains the differences in spending or whether individual physicians in high-spending regions have a greater tendency to intervene for th...

Health spending is expected to resume its rise as a share of gross domestic product (GDP) in the projection period, following 6 years of near stability, increasing from 13.5 percent in 1997 to an estimated 16.2 percent by 2008. This implies an approximate doubling of health spending, from $1.1 trillion in 1997 to $2.2 trillion by 2008. We anticipate a reversal in recent patterns of growth in pu...

We examine the effect of fiscal policy on sovereign risk spreads and investigate whether the interaction of fiscal variables with political institutions affect financial markets. Using panel data from emerging market countries, we find that revenue-based adjustment lowers spreads more than spending-based adjustment. Financial markets also react to the composition of spending. Cuts in current sp...

The impact of fiscal stimulus depends not only on short-term tax and spending policies, but also on expectations about offsetting measures in the future. This paper analyzes the effects of an increase in government spending under a plausible debt-stabilizing policy that systematically reduces spending below trend over time, in response to rising public liabilities. Accounting for such spending ...

In 2007, U.S. health care spending growth slowed to its lowest rate since 1998, increasing 6.1 percent to $2.2 trillion, or $7,421 per person. The health care portion of gross domestic product reached 16.2 percent, up from 16.0 percent in 2006. Slower growth in 2007 was largely attributed to retail prescription drug spending and government administration. With the exception of prescription drug...