Since NKN is designed with attack prevention in mind, it is necessary to review related attack types. Attack analysis and mitigation will be one of the important aspects of NKN development and future work.
Double spending attack. Double spending attack refers to the case where the same token is spent more than once. In classic blockchain systems, nodes prevent double-spending attack by consensus to confirm the transaction sequence.
Sybil Attacks. Sybil attack refers to the case where malicious node pretends to be multiple users. Malicious miners can pretend to deliver more copies and get paid. Physical forwarding is done by creating multiple Sybil identities, but only transmitting data once.
Denial-of-Service (DoS) Attacks. An off-line resource centric attack is known as a denial of service attack (DoS). For example, an attacker may want to target a specific account and prevent the account holder from posting transactions.
Quality-of-Service (QoS) Attacks. Some attackers want to slow down the system performance, potentially reducing the amount of network connectivity and data transfer speed.
Eclipse Attack. An attacker controls the P2P communication network and manipulates a node’s neighbors so that it only communicates with malicious nodes. The vulnerability of the network to eclipse attack depends on the peer sampling algorithm, and can be reduced by carefully choosing neighbors.
Selfish Mining Attacks. In a selfish mining strategy, the selfish miners maintain two blockchains, one public and one private. Initially, the private blockchain is the same as the public blockchain. The attacker always mine on the private chain, unless the length of the private chain is being caught up by the public chain, in which case the attacker publishes the private chain to get rewards. The attack essentially lower the threshold of 51% attack as it may be more efficient for other miners to mine the private chain than the public chain. Yet, as an economic attack, selfish mining attack needs to be announced in advance to attract miners.
Fraud Attacks. Malicious miners can claim large amounts of data to be transmitted but efficiently generate data on-demand using applets. If the applet is smaller than the actual amount of relay data, it increases the likelihood of malicious miners getting block bonus.