# Comparison of Distributed Tamper-Proof Storage Methods for Public Key Infrastructures
## 2 Related Work  
The previously mentioned drawbacks of modern PKIs have been addressed previously. In their research paper [1], [PERSON] et al. proposed a new methodology of creating a fully functional PKI that leverages the Ethereum Blockchain platform and its Smart Contract capabilities. Among other contributions, their proposed system offers a proper Preshared-Key (PSK) exchange and keystore concept that is decentralized and thus offers enhanced tamper-resistance. By using an Application Management Platform in conjunction with the public Ethereum Blockchain, the authors achieved an implementation that showed the real-world application potential of the proposed system. Their approach is, therefore, capable of replacing common CA implementations for their system. Trust and usability issues of common PKIs have also been identified by [PERSON] et al. [2] in their extensive exploration of potentials and challenges of Blockchain-based PKIs. The authors research four distinct usage scenarios that may benefit from the introduction of the DLT or the Blockchain in particular. Concepts such as the PKI, Pretty Good Privacy (PGP), and X.509 are shown to be capable of benefiting from the introduction of a Blockchain-backed approach for fixing common security problems and trust issues. The authors conclude that, at the state of writing, the Blockchain-based PKIs offers a large number of potentials, although there are major challenges to solve, especially concerning speed and scalability. Additional Blockchain-based concepts for a decentralized PKI have been proposed by [PERSON] et al. [3]. Their approach is focussing on being particularly applicable for the Internet of Things (IoT) and its special demands. The IoT is characterized, among other facets, by the dynamic joining and leaving of new or known network participants. Common PKI solutions, as the authors argue, are not always capable of coping with the corresponding scalability demands. Furthermore, the common monolithic PKI systems establish a single source of failure. In case of a PKI system outage, no trusted communication is possible anymore. To remedy these issues, the authors analyzed the abstract inner routines of common CA architectures and identified singular building blocks that can be decentralized. Using this method, they identified the verification component and swapped it out for a decentralized authorization component that offers a distributed information basis. To show the real-world applicability of the concept, an implementation using the HLF Blockchain Platform is provided. The results indicate that this solution is indeed applicable for IoT networks and is thus capable of replacing common monolithic PKI solutions. In practice, the IPFS is often used in combination with a Blockchain-based Smart Contract platform for handling logic. [PERSON] et al. [8] use the IPFS together with a private Ethereum-based application for secure data management that is especially suited for the IoT. Their approach is based upon a common IoT network structure, comprised of data consumers and producers. The exchanged data, which themselves shall be encrypted using specialized security measures, is stored decentralized on the IPFS. To allow for encryption and data verification, the Ethereum Smart Contracts allow for a custom programmability for the desired use case. In their specific setup, the authors used a Trusted Platform Module (TPM) for local key storage and verification operations. They were able to show that their system offers a throughput performance of eight transactions per second using a private Ethereum setup, thereby proving the real-world applicability. Though, the performance itself is mainly influenced by the data verification on behalf of the data consumers and producers. Another application example of the IPFS being employed in combination with the Ethereum Blockchain is provided by [PERSON] et al. [9].