This book constitutes the refereed proceedings of the 26th Nordic Conference on Secure IT Systems, NordSec 2021, which was held online during November 2021.The 11 full papers presented in this volume were carefully reviewed and selected from 29 submissions. They were organized in topical sections named: Applied Cryptography, Security in Internet of Things, Machine Learning and Security, Network Security, and Trust.

This book constitutes the proceedings of the 21st Nordic Conference on Secure IT Systems, held in Oulu, Finland, in November 2016. The 16 full papers presented in this volume were carefully reviewed and selected from 43 submissions. The focus of the conference is on following topics: Security, System Security, Network Security, Software Security, and Information Security.