###### Abstract  
Traditional identity management (IdM) solutions based on centralised protocols, such as Lightweight Directory Access Protocol (LDAP) and Security Assertion Markup Language (SAML), are where a central authority manages all the processes. This risks a single point of failure and other vulnerabilities. In response, decentralised techniques like blockchain and decentralised identities (DIDs) are being explored. This review paper performs a comparison of popular decentralised identity management (DIM) protocols, such as self-sovereign identity (SSI), against traditional centralised approaches such as LDAP and SAML. These decentralised identity management systems are being developed, keeping users' identity data as its highest priority. Additionally, this method eliminates the need for a central authority to manage and secure the system. To further explore the potential of decentralised identity management, this study delves into popular blockchain-based decentralised identity management systems such as uPort, Sovrin, EverID, Blockstack, ShoCard, and Hyperledger Indy. We analyse their underlying principles and compare them with the well-established centralised identity management solutions, focusing on key aspects such as scalability, security, and feasibility. However, despite their benefits and several worthy developments in this field, decentralised approaches are still not widely used. Through this study, we investigate both centralised and decentralised methods and review their strengths and weaknesses. By reviewing multiple research papers, this survey aims to provide an understanding and aid in selecting the most suitable identity management system for different use cases. c 2024 17 December  
personal information, digital IDs provide us the confidence to use the internet safely and conveniently [2]. Back in the early 1990s (see Figure 1), digital identity systems were very simple. They relied only on usernames and passwords. People had to sign up with various service providers, which required them to manage multiple identities. This quickly grew inefficient, and many people began using the same passwords on many sites, making security breaches more likely [4]. Personal data were vulnerable to hacking and unauthorised access due to the inadequate authentication techniques used. As the issues increased, more complicated methods of managing digital identities emerged. Digital identity security made major progress with the advent of single sign-on (SSO), biometrics-based authentication, and multi-factor authentication (MFA) [5]. These innovations addressed some of the issues in older authentication methods and made authentication both more secure and convenient. Despite these advances in digital identity management, traditional methods of storing and processing identities have generally remained centralised, where servers located and managed from a central location handle the storage and processing of user identities. We often use services like Google, Microsoft, Facebook, and Instagram, where identity verification is required, and these organizations, either directly or through providers like ID.me, Okta, or Auth0, manage and store identity data centrally. However, centralised systems come with inherent vulnerabilities. Since centralised systems have a single point of failure due to a single point of control, they are susceptible to various kinds of attacks, technical malfunctions, and data breaches [2]. Attackers may obtain sensitive identifiable information from a compromised central server, potentially leading to identity theft and illegal access to private and financial data. Furthermore, massive databases and significant computing power are commonly required for centralised identity systems to store and manage user data. This can lead to scalability issues. Also, as users' personal data are stored in centralised servers, it may raise concerns related to security and privacy of the data [6].