In May 2018, Bitcoin Gold (BTG) suffered its first large-scale 51% attack. The attacker carried out a double-spending attack by controlling 60% of the network's computing power, resulting in the theft of tokens worth $18 million. This attack directly threatens the foundation of decentralized trust by monopolizing computing power and tampering with blockchain transaction records. In compliance platforms such as HashKey Exchange , a multi-level defense system is being built through proof-of-stake (PoS) consensus and on-chain monitoring technology.
First, the attack principle and implementation conditions
The core of the 51% attack lies in controlling the dominant computing power of the blockchain network.
- Double spending (double spending) : The attacker sends tokens to the exchange on the public chain, while generating a longer fork chain on the private chain. When the exchange confirms the transaction, the attacker publishes the private chain, forcing the entire network to accept the version that does not include the exchange transaction, achieving asset reuse.
- Transaction Review : By refusing to package specific transactions, attackers can block payment confirmations from competitors or manipulate market liquidity. For example, a DeFi project triggered a trust crisis when attackers continuously reviewed withdrawal transactions, causing users to be unable to redeem their assets.
To carry out an attack, three conditions must be met:
- Centralized computing power : Bitcoin network requires more than 6 million TH/s computing power (about 230 million dollars of equipment investment), while small currencies such as BTG only need 50M computing power to launch an attack.
- Economic Strength : A failed attack could result in the loss of invested computing resources and frozen assets. For example, an attacker lost $430,000 worth of BTG due to a failed attack.
- Mining pool technology : By controlling the mining pool or leasing computing power (such as NiceHash platform), attackers can quickly aggregate computing resources. In 2024, an anonymous team leased 80% of the computing power and completed an attack on ETC within 1 hour.
II. Defense mechanisms and technological innovation
HashKey Exchange uses Proof of Stake (PoS) mechanism to replace traditional Proof of Work (PoW).
- Attack cost reconstruction : Attackers need to hold more than 51% of tokens as collateral, and the value of PoS chain tokens is usually much higher than the computing power cost of PoW chain. For example, after Ethereum switched to PoS, the attack cost increased by more than 10 times.
- Decentralization of verification nodes : By randomly selecting verification nodes to generate blocks, the risk of concentrated computing power is avoided. In the PoS network of HashKey Exchange, the top ten verification nodes only account for 28% of the entire network's collateralized tokens, effectively preventing single-point attacks.
HashKey Exchange collaborates with OKLink to deploy the Onchain AML platform, which achieves risk prevention and control through multi-dimensional data fusion.
- Computing Power Fluctuation Monitoring : Real-time tracking of mining pool computing power proportion, triggering an alarm when a mining pool's computing power suddenly increases by more than 30%. In 2024, the system identified a mining pool injecting abnormal computing power through a zombie network and timely blocked the attack chain.
- Transaction behavior analysis : Combine on-chain transfer data (such as large fund flows) with social media sentiment to build a dynamic risk model. When a token's on-chain transaction volume surges but public opinion is abnormally high, the system automatically marks it as high risk.
- Cross-chain collaborative defense : Share threat intelligence with platforms such as Chainalysis and track cross-chain fund paths. For example, when a hacker transfers stolen tokens to the Solana chain through a cross-chain bridge, the system freezes assets in a timely manner through address tag matching.
Practice path of compliance platform
- Smart Contract Audit : HashKey Exchange's formal validation tool detects contract vulnerabilities, such as latent risk points such as unrestricted approve function calls, and fixes security vulnerabilities before deployment.
- Application of sharding technology : By dividing the blockchain into multiple sub-chains to process transactions, the computing power demand of a single chain is reduced. For example, a sharding chain project disperses the computing power of the entire network to 200 shardings, which increases the cost of attacking a single sharding by 200 times.
- Cold wallet storage : HashKey Exchange stores 98% of user assets in an offline cold wallet, preventing private key leakage through multi-signature and hardware security module (HSM).
- Dynamic take profit and stop loss : Users can set automatic execution of trades when the price fluctuation of Bitcoin exceeds the threshold, avoiding missing the best operation opportunity due to emotional interference. A user used this function to automatically position squaring when the price of Bitcoin plummeted by 30%, reducing losses by 70%.
The essence of blockchain 51% attack is a game between computing power monopoly and decentralized trust. HashKey Exchange reduces attack risk by 85% through PoS consensus, on-chain monitoring and smart contract technology, while maintaining the innovation vitality of blockchain. In the era of Web3.0, understanding attack principles and defense strategies is the key to building a secure and trustworthy digital financial ecosystem.