Threshold Efficient Cryptosystem : LAP Lambert Academic Publishing : 9786200221285 : 6200221286 : 13 Jun 2019 : This book is written for the benefit of the students who are pursuing their Ph.D (CSE), MTech., MCA, Msc (Comp), BTech of various universities across India and Master Degrees in foreign Universities. Especially the content of this book acts as a basis for the research scholars and post doctoral in the area of information security. This book aimed a cryptosystem, rather than use of a single or conjunct with limited nonce core-key directly in cryptographically process data, one can use core-key as master key to derive unlimited sub-keys, and use of these sub-keys in cryptosystem. In this work we are using pseudo-random bit generator for re-keying. Simulation is performed using Java 1.6 and IDE Netbeans 6.3, tested the same with sample data and obtained results are presented. This mechanism adopted as a communication service in a chat application and simulated the Man-in-the-Mid