The number of transactions performed electronically is rising fast. Every day people use the Internet for a variety of services, including accessing personal information, electronic purchases, e-banking, as well as interactions with government bodies. As securing these transactions requires strong authentication, electronic authentication tokens, or digital credentials, are employed. Up to now, however, the digital credentials employed for authenticating or identifying users do not respect users' privacy. They invariably reveal the identity of the holder even though the service may require much less information, for instance only confirmation that the user is a teenager or he/she is eligible for certain social benefits. In contrast to that, the new concept of Attribute-based Credentials (ABCs) allows a holder to reveal only the information required by the application, without giving away full identity information, preserving in this way the privacy of service users. Such digital credentials, consequently, can be the cornerstone of a trustworthy and at the same time privacy-protecting digital society. In particular for Greece, ABCs can be the main ingredient of the forthcoming digital identification card as well as the electronic health card that will, soon, be introduced towards the reform of the public sector and the strengthening of e-Governance in the country. ABC4Trust is a European project (https://abc4trust.eu/) whose goal is to address the federation and interoperability of existing technologies that support trustworthy and privacy-preserving ABC-based user authentication.