This book constitutes the refereed post-conference proceedings of the 19th International Conference on Information Security, ISSA 2020, which was supposed to be held in Pretoria, South Africa, in August 2020, but it was held virtually due to the COVID-19 pandemic. The 10 revised full papers presented were carefully reviewed and selected from 33 submissions. The papers deal with topics such as authentication; access control; digital (cyber) forensics; cyber security; mobile and wireless security; privacy-preserving protocols; authorization; trust frameworks; security requirements; formal security models; malware and its mitigation; intrusion detection systems; social engineering; operating systems security; browser security; denial-of-service attacks; vulnerability management; file system security; firewalls; Web protocol security; digital rights management; and distributed systems security.