## 1 Introduction  
The development of information and communication technology provides services to various fields. In particular, the development of mobile technology has made ubiquitous services possible. However, as technology advances, security is being emphasized more and more. The existing method of entering an ID and password is highly likely to leak all information if the server is attacked. Therefore, various methods for secure authentication have been studied. In Korea, user authentication in financial institutions has been performed by using public certificates. Still, this has been inconvenient to many users due to required Active X installation and usage difficulties. Accordingly, since November 2020, the Republic of Korea has abolished the accredited certificate system and introduced a multi-level authentication method that utilizes various authentication stages. For example, these authentication stages may include two or more types of simple passwords, Kakao certificates, OTP numbers, and biometrics [1].  
Blockchain, which has recently been attracting attention from many researchers, guarantees integrity based on a decentralized and distributed trust structure and enables the implementation of an authentication system that cannot be forged or tampered with. By combining blockchain technology with Internet-based technologies that require perfect security, a system can be developed that applies both data integrity and strong security.  
Blockchain technology encrypts transactions to protect data, includes various information in blocks, connects them to chains, and continuously generates blocks at short intervals, making it difficult for hackers to prepare time and system resources for attacks [2; 3; 4].  
The use of biometric technology for user authentication is also increasing. In iPhone and Android smartphones, biometric technologies such as fingerprint recognition and face recognition are used along with simple passwords in order to strengthen the mobile device's security. Additionally, biometrics has begun to be used as a new authentication method for online transactions in the financial field. In particular, facial recognition security systems are easy to use and not easy to forge, so these can help prevent security accidents related to finance [1].  
Therefore, this study proposes a multi-level authentication system using blockchain-based technologies such as DID (decentralized identity) technology and biometric recognition technology.  
The following are requirements in the process of designing a secure and effective multi-factor authentication system.  
1. Account information required for user authentication must be free from forgery or alteration by hackers;
2. In terms of security, user authentication must be secure;
3. The user authentication process should be performed in a simple or easy way;
4. During the authentication process, if a legitimate user cannot be identified, even if the user is a legitimate user, that user should not be incorrectly authenticated (miscertified). After entering the ID and password when starting the service, if authentication is performed using facial recognition technology, this information is stored in the blockchain. Since the user's facial recognition information is accumulated in the blockchain, the integrity of the data can be guaranteed for purposes of identity authentication.  
The composition of this study examines the concept of DID with related research in Section 2 and examines various platforms that have been developed based on DID and DID Auth standards, as well as neural network algorithms that can be applied to them. In Section 3, the system structure proposed in this study is designed and explained, and Section 4 describes the development of authentication systems. Finally, Section 5 provides the conclusion of the study and describes future research tasks.