The Estonian Mobile-ID Implementation on the SIM Card

Abstract

Mobile-ID is an eID solution that can be used for authentication and digital signing. It has been transaction for more than a decade, and it is popular in Estonia. As of May 2022, more than 251 000 Mobile-IDs are in use, and, on average, 10 million operations are completed each month [1]. The solution relies on a special Mobile-ID functionality built into a phone SIM card. There is publicly available documentation about Mobile-ID [2], but it mainly describes the communication between the e-services implementing Mobile-ID support and the Mobile-ID backend. Not much information is publicly available on how Mobile-ID functionality is implemented on the SIM card, how it interacts with the phone and how it communicates with the Mobile-ID backend. In this work, interactions between the SIM card and the phone are documented. Additionally, the communication between the SIM card and the Mobile-ID backend is described, as well as how Mobile-ID service SMS are used to perform Mobile-ID transaction.