# Blockchain Implementation Method for Interoperability between CBDCs
## 1 Introduction  
Currently, we use computers and mobile phones to make online remittances and e-commerce transactions on networks such as the Internet, and we exchange data in online transactions. Exchange data has different security requirements depending on the situation. For example, messengers have low integrity requirements for data transmission. However, online transactions require high-integrity data to be used in authentication and transaction authentication. We rely on trusted third-party intermediaries for data integrity and pay high brokerage costs. In online transactions, brokerage costs limit daily transactions at low prices because they raise transaction costs, and non-reversible deals are theoretically impossible. Bitcoin proposed an electronic cash system directly trades without intermediaries between individuals based on cryptographic proofs instead of third-party trust [1; 2; 3]. Since Bitcoin was released to the world, many cryptocurrencies have been released. Many cryptocurrencies have been proposed to deal with the shortcomings of Bitcoin or to solve many global problems. Ethereum is a platform that supports smart contracts and decentralized applications (DApps) for monetary functions [4; 5; 6]. Smart contracts can express the contents of the contract in a language (Solidity) and automatically execute the contract when the predetermined conditions are satisfied. They can automate by combining insurance, real estate, and copyright. Ripple is a cryptocurrency to support real-time money transfers among banks around the world [7]. International remittances typically use SWIFT (Society for Worldwide Interbank Financial Telecommunications). SWIFT takes two to three hours to complete a trade, and different banks have different fees. Ripple aims to efficiently and immediately process remittances anywhere in the world to replace SWIFT. Additionally, Ripple wants to reduce the cost of remittance by using cryptocurrency. As such, different cryptocurrencies have been proposed to solve real-world problems. Countries should prepare for cashless societies to avoid problems. A cashless society is a society in which cash has decreased due to the activation of non-cash payment methods such as credit cards and mobile payment methods. Countries entering cashless societies (Sweden, New Zealand, UK) have common problems with weakening cash access, banking and consumption activity of vulnerable groups, and weakening public currency distribution systems. Central banks study the Central Bank Digital Currency (CBDC) in preparation for a cashless society [8; 9]. Facebook announced the cryptocurrency Diem (formerly known as Libra) in June 2019 [10]. Diem has announced plans to use a single, universal digital currency. Diem guarantees its cryptocurrency through the Diem Reserve, which consists of real-asset collateral. The Diem Reserve provides value assurance by organizing funds into a collection of gold, dollars, euros, bank deposits, and short-term government securities. Diem can be used globally by Facebook's 2.3 billion users (as of January 2019). However, governments--such as that of the United States and European countries--have expressed concern, and the US House of Representatives proposed a law to stop Diem. This objection to Diem hinged on the assertion that the pace of Diem infringes upon the sovereignty of a government's monetary system and can devastate the current global financial system. In December 2019, the central bank of Bahamas began the Sand Dollar project. Sand Dollar (a digital version of the Bahamian dollar) was officially launched in October 2020 through authorized financial installations (AFIs). The People's Bank of China announced its high-priority CBDC research and development in 2020. China wants a globally accepted digital currency using the yuan-based CBDC [11]. As the largest trading country, China occupies more than 10% of the world's trade [12] and allows payments in RMB for trade settlements.