# Secure Delivery Scheme of Common Data Model for Decentralized Cloud Platforms
## Materials and Methods
### Materials
#### 2.1.3 Blockchain  
Blockchain technology is a technology that transparently records transaction history on a ledger that anyone can read and copies and stores it on multiple computers. Therefore, since this technique is based on individual transactions, there is no need for a central administrator. In addition, because multiple computers verify the records, it is difficult to forge or alter them by third parties. The most representative applications based on blockchain technology are smart contracts, virtual currencies such as bitcoin, etc. Among them, decentralization, a characteristic of bitcoin, facilitates the sharing of control between users and ID providers, allowing users to manage their identities [13].  
The NEXTLEAP system was developed for the purpose of alternative decentralization and enhanced privacy protection. Built as a federated ID system, this system uses algebraic MAC-based blind signatures to enhance privacy protection. It was also verified by the stability of messages through distributed IDs for messages allowed between different servers [14]. The blockchain protocol\"Ouroboros Praos\" was developed to demonstrate the stability of security by delaying transmission in a semi-synchronous setting for complete conversion [15].  
The chainAchor system is introduced to utilize identities that can be provided for privacy protection purposes. This system can read/verify transactions on the authorized blockchain, create a read-only list of public keys of anonymous members, and perform simple lookups on entities on the blockchain [16]. It also provides a protocol for an identity management system built into Bitcoin. This facilitates the sharing of control between users and ID providers, and verifies the relationship between the rights and responsibilities of users and ID issuers [13].  
In addition, various studies are being conducted to improve security issues and operate more efficient systems through blockchain. A new practical paradigm named Thunderella was proposed through the replication of the system state by combining the asynchronous path and the synchronous alternative path [17]. It also provides the first official analysis of Bitcoin's target (re)calculation capabilities in crypto settings. It extends the q-bounded motive model of the Bitcoin backbone protocol, which presented the properties of Bitcoin's basic blockchain data structure, and shows how to build a strong public transaction ledger on top of it [18]. In order to reinforce the security issues of the developed system, abstract blockchain protocols can be defined and appropriate security properties of these protocols can be identified. To this end, it meets [PERSON]'s blockchain protocol and proves that these properties are sufficient for general applications [19]. For proof of security, Bitcoin has presented a ledger of (G) UC models such as Canetti, and a process has been proposed with the aim of achieving function [20]. A blockchain-based secure data sharing mechanism for VN (Vehicular Networks) is proposed. In order to efficiently manage service provisioning, we have introduced an edge service provider with regular nodes [21]. The dual decentralized network blockchain utilizes a licensed blockchain for increased processing speed and security, and allows the system to be used openly and without permission to application developers while dividing the system into multiple layers [22].  
The public blockchain is based on a distributed ledger and is classified as a public ledger limited to P2P-based financial transactions in terms of opening and managing the transaction ledger [23]. A private blockchain to solve these limitations can be used to share CDM data by authorized users such as the medical sector. In addition, this technology method can provide functions as it becomes easier and safer to participate in data services by using digital identifiers [24].