## Introduction
Blockchain technology, which powers cryptocurrencies such as Bitcoin and Ethereum, promises a high degree of security and decentralization. However, despite these advantages, blockchain is not immune to various types of attacks. One such attack is the “Alternative Historical Attack” or blockchain reorganization attack. In this article we will look at the mechanism of this attack, its consequences and precautions.
## Attack Mechanism
A blockchain reorganization attack occurs as follows:
1. **Sending transaction**: The attacker sends a transaction to the recipient, which is included in the current block chain.
2. **Mining an alternative fork**: At the same time, the attacker begins to mine an alternative fork of the blockchain, which contains another transaction that returns the same coins back to the attacker.
3. **Transaction confirmation**: The recipient sees that the transaction has received n confirmations and considers it valid, sending the product or providing the service.
4. **Chain Reorganization**: If an attacker has enough computing power, he can create a longer chain of blocks than the current one. In this case, the network will accept the new chain as the main chain and the original transaction will be reversed.
## Computing power requirements
To successfully carry out a blockchain reorganization attack, an attacker requires enormous computing power. This is due to the need to create a longer chain of blocks than the one that already exists on the network. The more confirmations a transaction has, the more difficult and expensive it becomes to carry out such an attack.
## Consequences of the attack
The main consequence of a blockchain reorganization attack is that the recipient may lose money or assets. After receiving n confirmations, the recipient considers the transaction valid and sends the product or service. However, if the attacker issues a longer chain, the original transaction is reversed and the coins are returned to the attacker.
## Precautionary measures
To minimize the risks associated with a blockchain reorganization attack, it is recommended:
1. **Increasing the number of confirmations**: The more confirmations a transaction has, the more difficult it is for an attacker to carry out an attack. It is recommended to complete payments only after receiving sufficient confirmations.
2. **Network Monitoring**: Constantly monitoring your network for suspicious activity can help identify attack attempts.
3. **Use Additional Security Measures**: Implementing additional security measures such as multi-signatures and time delays can improve resistance to attacks.
## Conclusion
A blockchain reorganization attack poses a serious threat to the security of transactions in blockchain networks. Despite the high computing power requirements, such attacks are possible and can lead to significant losses. Following recommendations for increasing the number of confirmations and implementing additional security measures will help minimize risks and protect user assets.
For a more detailed study of attack vectors on the blockchain, you can read the materials at the link: [attack vectors on the blockchain](https://www.apriorit.com/dev-blog/578-blockchain-attack-vectors).
