Abstract
The 51% attack is a technique which intends to fork a blockchain in order to conduct double-spending. Adversaries controlling more than half of the total hashing power of a network can perform this attack. In a similar way, n confirmation and selfish mining are two attack techniques that comprise a similar strategy to the 51% attack. Due to the immense attacking cost to perform the 51% attack, it was considered very unlikely for a long period. However, in recent times, the attack has befallen at a frequent pace, costing millions of dollars to various cryptocurrencies. The 51% attack strategy varies based upon the adopted consensus mechanism by a particular cryptocurrency, and it enables attackers to double-spend the same crypto-coin, restrict transactions, cancel blocks, and even have full control over the price of a cryptocurrency. A crypto-coin with a low hashing power is always jeopardized by the 51% attack due to the easily attainable hashing. In this paper, we analyze the real impact of the 51% attack, revealing serious weaknesses in consensus protocols that made this attack possible. We discuss the five most advanced protection techniques to prevent this attack and their main limitations. We conclude that in most cases, security techniques fail to provide real protection against the 51% attack because the weaknesses are inherited from the consensus protocols.
Highlights
Blockchain is an emerging technology that allows performing digital transactions within a short period [1]
We discuss seven major security threats that jeopardize the blockchain network; We reveal the limitations of the consensus mechanisms by classifying them in several attacks; We define the majority hash rate problem and point out the consequences of the attack techniques; We analyze five security protection mechanisms specific to the 51% attack and demonstrate their limitations against the 51% attack exploitation
Our analysis indicates that the consensus mechanisms comprise severe limitations, resulting in a low quality of experience (QoE) of the network participants [25]
Summary
Blockchain is an emerging technology that allows performing digital transactions within a short period [1]. In addition to crypto-transactions, it is leveraged for various other purposes, such as insuring intellectual property, generating financial contracts, tracing food production, and tracking supply chains [2] The rise of this technology has been obstructed from time to time by various pernicious attacks. After Bitcoin appeared, new cryptocurrencies evolved to take advantage of the blockchain network The more this technology was adapted, the more it drew the attention of potential attackers. We discuss seven major security threats that jeopardize the blockchain network; We reveal the limitations of the consensus mechanisms by classifying them in several attacks; We define the majority hash rate problem and point out the consequences of the attack techniques; We analyze five security protection mechanisms specific to the 51% attack and demonstrate their limitations against the 51% attack exploitation.
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