# Decentralized and Secure Blockchain Solution for Tamper-Proof Logging Events
## 2 Related Work  
There are various studies in the state of the art that focus on the use of blockchain technology for the registration of information. In the context of this work, we highlight those solutions focused on the persistence of activity records. Log files generated by systems cover a wide range of possibilities, including user access, security incidents, and events generated by both applications and networks, among others [10]. The auditing processes also pursue the persistence of log files, which may seek to know the degree of compliance an entity has with a specific regulation [1]. Outstanding research proposes an auditable system using Exonum [11], a private blockchain with several salient features. These include using the Byzantine Fault Tolerance  
Figure 1: Use case on secure access in router management. (BFT) consensus algorithm, the ability to execute smart contracts, and the use of public blockchains to additionally establish periodic trustworthiness via Bitcoin. This system integrates with a Security Information and Event Management (SIEM) solution to acquire events via the Syslog standard. Its hybrid architecture guarantees the immutability and integrity of logs by storing them both on-chain, using hashes, and off-chain in a local cluster. At the same time, it allows efficient access and proper management of security events. Nevertheless, the level of transparency and reliability of the system is compromised by storing a part of the data outside the public blockchain. In addition, the use of smart contracts complicates its implementation. A different study [12] uses Hyperledger, a private blockchain implemented to store log files encrypted by users presumably before they are sent. Storing log files directly on the blockchain raises concerns about ensuring data integrity as it becomes impossible to verify that the data have not been tampered before being included in the blockchain. Additionally, similar to the previous scenario, implementing a private blockchain reduces the transparency and reliability of the system. In [13], a system is proposed to help auditors verify compliance with regulations using Bitcoin, a public blockchain that uses the proof of work (PoW) consensus mechanism. Data are stored both on-chain and off-chain, but the system is not designed to store events generated by network equipment. In addition, neither the price of fees nor the number of transactions per second of the Bitcoin network are scalable for use in this context. Several authors propose BlockAudit [14], a secure and transparent system for auditing logs in charge of storing the actions executed in the system. It records on-chain data through the private Hyperledger blockchain, so it lacks transparency and reliability compared to public blockchains. An outstanding work [15] has proposed an autonomous log storage management system for IoT devices that uses both public and private blockchains using Ethereum and Hyperledger, respectively. The system stores the content of off-chain logs and their signatures on the private blockchain, whose transactions are managed through smart contracts. A summary of these transactions is signed and stored in the public blockchain, providing greater transparency and reliability. However, there is still a risk of tampering with the blocks on the private blockchain before they are sent to the public blockchain. Additionally, the system is subject to the transaction price volatility imposed by Ethereum. Moreover, [16] introduced the blockchain-based secure log management system for cloud computing (BCALS) using Multichain, a private blockchain that stores log messages on-chain. The data contained in the event logs are sent to Elasticsearch for further exploitation, an open-source project used to search, analyze, and visualize large amounts of information in real-time. As in previous cases, the use of a private blockchain implies a compromise in the level of transparency and reliability of the system.