As the technology era starts to grow larger and internet becoming a lifestyle, more people starts to use it without realizing that the data sent through the internet might be taken by unauthorized person. The intruder might look what’s inside the data or modify it. This person is called man in the middle (MITM). This scenario could take place even when it’s encrypted, for example using RSA algorithm as one of the most secure encryption these days. Moreover, many people don’t know how to overcome MITM by the use of the interlock protocol, which has been introduced twenty six years ago. In this final project, a simulation program has been successfully made to help people, understand about RSA, MITM attack and interlock protocol. It starts by making keys for RSA algorithm, later the program will show how MITM works and the use of interlock protocol, where the message is divided into two parts and sent simultaneously. Each part of the message can be decrypted but it will be unreadable. The simulation program runs perfectly, as long as the input from the user does not exceed the rule of using the program. The RSA algorithm used in this program is a bit different with the real RSA, where the user had to determine the values of p, q, and e for making the keys. This program can be improved by adding other encryption algorithms or creating better animation for the simulation.