AbstractCurrently live messenger is oftenly used as a media for communication among staff in the office or among students doing projects and working in groups or teams. The problem is that live messenger runs under a network with limited security and therefore facing threats such as interception, authenticity, interruption and fabrication. The purpose of this research is to design security protocol on live messenger that ensures authenticity and data or message confidentiality whenever data/messages are sent from one user to another user. The protocol is designed to ensure that no one except the authorized user are allowed to communicate to each other. The proposed protocol is an end-to-end protocol, where each user can only comunicate once...