An interactive webinar on cyber security entitled “Application of Number Theory in Cyber Security: Few Illustrations through SageMath” was organised by the Department of Mathematics, The Bhawanipur Education Society College on 20.06.2020 from 11.30 am. Dr. Avishek Adhikari, a professor of Mathematics at the Presidency University was the invited speaker at the webinar. In the beginning of the webinar, Dr. Samir Kanti Datta, Vice-Principal (Science) of The Bhawanipur Education Society College delivered the welcome address. Then Dr. Adhikari was introduced to the audience where he was mentioned to be a distinguished cryptologist who has obtained several awards and honours for his works in the field of cryptography including President of India Medal, ISCA Young Scientist Award, and NANUM fund by International Mathematical Union (IMU). Following the introduction, Dr. Adhikari started delivering his lecture on the application of number theory in cyber security. He began by discussing several online threats and their impacts on the life of an ordinary internet user. Then he mentioned that cryptography can be a potential saviour in this scenario and introduced the audience with several aspects of the field including the public key cryptosystem. He illustrated through SageMath the application of modular arithmetic and other fields of number theory in the area of public key cryptosystem which helps in securing the cyber world. His talk ended by mentioning as few important references for the interested readers. Following the talk of Dr. Adhikari an interaction session was held where the participants posed their questions. Among the participants there were several students and teachers of colleges and universities spread over the state. The webinar ended with the vote of thanks from the organiser.