# Trusted Third Party Application in Durable Medium e-Service
## 1 Introduction
In response to the above-mentioned problems, several solutions for data protection have been developed. At this point, however, we would like to draw attention to the legal solutions existing in Poland. They are created to protect the rights of the client and impose the need to store documents regarding the client (e.g., contracts, regulations of services provided, etc.) on the so-called durable medium. This solution indicates that electronic documents should be stored in infrastructure independent of any of the parties, and the process of sharing these documents with all parties and their storage should be monitored. Therefore, there is a need to use a so-called trusted third party (TTP) that can provide infrastructure for storing and processing electronic documents, as well as act as an arbiter of processing operations of these documents. In summary, there is a need for secure and trusted services for the storage and processing of electronic documents. It is very important to store data securely, in order to protect personal data and other confidential information from unauthorized access. Additionally, trusted storage of electronic documents ensures their integrity and immutability, which is important in business transactions. Safe storage of electronic documents also helps to protect them against loss, for example as a result of a computer failure or damage to the data medium. In addition, some legal regulations (e.g., in Poland) force companies (especially banks) to store and process documents using a TTP. Therefore, secure and trusted electronic document storage services are very important in today's world. This is reflected in the market demand for e-services for the safe and trusted transmission, processing, storage, and sharing of electronic documents, especially those that meet the requirements of a durable medium. The use of cryptographic methods and a trusted third party allows for the development of a secure and trusted e-service of a durable medium proposed in the paper. The main contributions proposed in the paper can be summarized as follows:* A novel, secure, and trusted e-service as a durable medium is proposed;
* The presented approach is secure because it utilizes cryptography combined with blockchain technology, and is trusted thanks to the use of trusted third party infrastructure and an immutable database;
* The proposed e-service is designed to meet the requirements of Polish law, related to the durable medium;
* The key feature of the presented approach is a unique combination of decentralized blockchain with the TTP, which increases the security and reliability of electronic document storing and management;
* The presented solution is oriented toward big financial institutions or telecommunications companies that provide services to thousands of users (however, it can be applied in other industrial areas where there is a need for processing electronic documents with large numbers of customers);
* The case-study example was designed and experimentally verified by the implementation of the blockchain using the Hyperledger Besu platform;
* The proposed e-service was developed based on real market needs and was implemented in the company's real environment;
* The presented solution is focused on practical implementation and therefore is supported and developed in cooperation with the \"Perceptus Sp. z o. o.\" [3]-IT company from Poland. The research methodology presented in the paper is based on theoretical foundations and scientific analyses, as well as on practical experience regarding e-service implementation. The main context of the research was derived from market and industry needs. In 2018, the Polish Office of Competition and Consumer Protection (OCCP, UOKIK in Polish) inspected banks in terms of the method of transmitting information on changes to contracts on a durable medium [4].