An Analysis of Attacks on Blockchain Consensus
This addresses the problem of transaction security for blockchain users and merchants, providing incremental insights into attack thresholds.
The paper tackled the security of blockchain transactions against double-spend attacks by developing a mathematical model to analyze how factors like confirmation depth and attacker mining power affect the value that can be secured, finding that a single confirmation protects against attackers with up to 1% extra mining power, while 72 confirmations eliminate profit for attackers with less than 40% extra power.
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. Our model quantifies the importance of several factors that determine the attack's success, including confirmation depth, attacker mining power, and any confirmation deadline set by the merchant. In general, the security of a transaction against a double-spend attack increases roughly logarithmically with the depth of the block, made easier by the increasing sum of coin turned-over (between individuals) in the blocks, but more difficult by the increasing proof of work required. In recent blockchain data, we observed a median block turnover value of 6 BTC. Based on this value, a merchant requiring a single confirmation is protected against only attackers that can increase the current mining power by 1% or less. However, similar analysis shows that a merchant that requires a much longer 72 confirmations (~12 hours) will eliminate all potential profit for any double-spend attacker adding mining power less than 40% of the current mining power.