# A Blockchain-Based Decentralized Public Key Infrastructure Using the Web of Trust
## 2 Related Works  
Several previous studies have examined various certification services and digital identity systems using distinct approaches. The application of blockchain technology as a means to enhance PKI systems has emerged as a prevalent research focus within this domain. [PERSON] et al. introduced CertLedger [13], a blockchain-based PKI solution that leverages the blockchain as a public ledger for storing CA operations, certification, and revocation information. It helps mitigate split-world attacks, as clients can verify TLS certificates by monitoring logs post-confirmation of the latest block. However, CertLedger still struggles to prevent CAs from issuing rogue certificates. Building on the concept of transparency, the Decentralized PKI Transparency (DPKIT) system [14] was proposed to ensure the verifiability of certificates throughout their issuance and revocation life cycle. By facilitating public auditability, DPKIT enhances the ability to verify the authenticity of certificates and identify any fraudulent activities. [PERSON] et al. [15] presented a semi-decentralized PKI system that addresses the scalability challenge of managing a vast number of certificates. Their approach utilizes a TP-Merkle tree data structure, which, in combination with smart contracts and cryptographic evidence, enables an automated indemnification system. It also redefines the proof-of-violation (POV) protocol to achieve mutual nonrepudiation between the CA and the user and helps the domain monitor CA activities. BPKI [25] prevents domain name preemption attacks by introducing auditors and a multi-layered architecture to supervise CA operations and enhance blockchain transaction rates via delegated PBFT. While effective in preventing fraudulent certificate issuance and improving throughput, its reliance on multiple auditors can introduce delays in the certification process. CBPKI [16] encompasses a cloud-based blockchain PKI that utilizes cloud computing and blockchain technology to enhance security, particularly in preventing DoS attacks by shifting CA operations to the cloud. It also improves performance by removing CRL. However, the certification phase remains under CA oversight, which perpetuates the threat of malicious certificate issuance when a CA is compromised. CertChain [17] is another decentralized and tamper-proof audit scheme built on Ethereum. It introduces a new data structure CertOper to store all certificate-related operation information. It also proposes a new entity bookkeeper, serving as a leader to manage certificate operations within the network. Users are required to validate certificates with the assistance of the bookkeeper, which introduces a security vulnerability: a compromised bookkeeper can exploit users to create a malicious certificate. In the quest for a fully decentralized authentication system, Certcoin [18] does not rely on trusted third parties for identity retention. It employs  
Figure 1: Overview of the proposed decentralized PKI based on blockchain and the WoT. the proof-of-work concept similar to Bitcoin, Namecoin, cryptographic accumulators, and distributed hash tables. In a similar vein, [PERSON] et al. introduced Cecoin [19], which addresses the single point of failure associated with certificates on the Bitcoin network by replacing CAs with miners. Nevertheless, this method introduces unnecessary complexity to the revocation process when it is needed. To detect misbehaving CAs or misused certificates, the log-based PKI approach was proposed. This approach uses a cryptographically secure, append-only log to maintain a record of legitimately issued certificates, thereby enhancing the revocation processes. Certificate Transparency (CT) [9] stands out as the most widely adopted log-based PKI system, utilizing append-only Merkle Hash Trees to manage and efficiently verify TLS certificates.