Entropy is a basic and important concept in information theory.It is also often used as a measure of the unpredictability of a cryptographic key in cryptography research areas.Ubiquitous computing (Ubi-comp) has emerged rapidly as an exciting new paradigm.In this special issue, g5210t-p90 we mainly selected and discussed papers related with ore theories based on the graph theory to solve computational problems on cryptography and security, practical technologies; applications and services for Ubi-comp including secure encryption techniques, identity and authentication; credential cloning attacks and countermeasures; switching generator with resistance against the algebraic and side channel attacks; entropy-based network anomaly detection; applied cryptography using chaos function, information hiding and watermark, secret sharing, 3 piece horse wall art message authentication, detection and modeling of cyber attacks with Petri Nets, and quantum flows for secret key distribution, etc.