Cryptography is a complex area in the computer science field due to the complexity of the mathematics involved. The main goal of this paper is to discuss how we can take an advantage of the online interactive tools to facilitate this complex topic. These interactive tools can enhance the students learning better than the traditional way especially when we teach mathematic concepts. We are going to illustrate an online interactive tool that uses the Modular Arithmetic in a virtual environment. A case study was conducted on a group of students from the King Abdulaziz University. The result of evaluating the tool indicates that this tool has good usability in terms of learnability, usefulness, ease of use, and outcome.