This two-volume set LNCS 12918 - 12919 constitutes the refereed proceedings of the 23nd International Conference on Information and Communications Security, ICICS 2021, held in Chongqing, China, in September 2021. The 49 revised full papers presented in the book were carefully selected from 182 submissions. The papers in Part II are organized in the following thematic blocks:​ machine learning security; multimedia security; security analysis; post-quantum cryptography; applied cryptography.