## 1 Introduction  
In our digital world, where most things tend to be online and scams, frauds, and identity theft are rising, digital identity plays a crucial role in forming a digitized ecosystem. Digital identity has undoubtedly grown in importance internationally [1]. Digital identity information was commonly stored in traditional databases using encryption mechanisms to provide confidentiality and integrity, as well as replication processes to provide availability. Digital identity is the cornerstone of a digital economy [2]. So, the next evolution of digital identity involves storing digital identity information in a trusted Ledger Distributed Technology like blockchain. Blockchain is a technology that provides greater trust in the digital world [3]. As noted by [PERSON] et al. [4], blockchain technology can enhance security, privacy, and user control over personal data. Blockchain technology offers some key advantages: (i) reduces the risk of failures; (ii) ensures transparency; (iii) offers immutability; (iv) reduces risks of fraud and tam pering; and (v) provides traceability. Blockchain can provide a decentralized solution for managing sensitive personal information through programmable smart contracts. This technology permits, through smart contracts, the conversion of data into tokens. Tokens are intangible objects with public and private attributes. This is an important mechanism to provide confidentiality. Various countries around the world are exploring blockchain technology for digital identity, for example, China [5,6], Germany [7,8], and the United States [9]. Furthermore, several works have focused on conveying the digital identity using blockchain [2,10, 11, 12, 13, 14]. However, we have identified the following limiting aspects: (a) Most of them are self-sovereign identity mechanisms, and the figure of a legal authority certifier like a government has seldom been explored. (b) Absence of mechanisms to link different entities: in a digital identity ecosystem, people's digital identity must be interrelated with other entities (physical or virtual objects). For example, a person should usually be linked to different entities, such as a birth certificate, a passport, and a visa, as well as to physical things, like cars and houses. (c) Lack of transactional costs evaluation: it includes how much it would cost for governments and end-users to have a digital identity ecosystem. This paper focuses on how to establish the relationship process between types of users and different entities. We propose the creation of a digital identity ecosystem, which is built by different tokens that can be regulated or not by a government. The government is a crucial actor that can create entities. For each entity created, the government generates a digital identity token, of which the entity is the owner. Each entity can link other tokens, which were previously certified or not by the government, into their digital identity token, thereby generating a digital tree of tokens. The contributions of this research are abstracted as follows:  
1. We propose a digital identity ecosystem that accommodates both government-certified and uncertified tokens. The government can create different entities, each one with its own digital identity token. Each entity decides the tokens to link and form its identity through tokens. 2. The creation of digital identity tokens avoids the duplicity characteristic. It means that the government can only create a digital identity token for each entity. 3. We provide certainty about the transaction costs that the government, end-user, and an external entity (a University) would incur by having this ecosystem. 4. We describe the feasibility of having a digital ecosystem from three perspectives: economic, technical, and social. The paper is organized as follows: Section 2 cites and explains important works focused on the study of digital identity with solutions applying blockchain. Section 3 proposes our tokenized digital identity system, which is described more technically in Sections 4 and 5.