Teaching interactive cryptography: the case for CrypTool Saša Adamović 1 , Irina Branović 2 , Dejan Živković 3 , Violeta Tomašević 4 , Milan Milosavljević 5 Abstract – The theory and applications of cryptography are complicated and hard to follow for undergraduate students with less mathematical background. For this reason, instead of plain theoretical teaching, we applied different, interactive approach. Open-source CrypTool software allowed us to practically demonstrate all current private and public-key algorithms and protocols. This paper describes our teaching model and experience. Positive feedback received from students confirms the advantages of adopted approach with respect to traditional teaching. Keywords – education, cryptography, interactive teaching, CrypTool I. INTRODUCTION Cryptography course as part of computer science curriculum has become a necessity, considering that it nowadays serves as the basis for data communication security, information and network security. For today’s computer professionals, secure data storage and communication have become vital competencies, unlike before when cryptography was considered to be a secret science. However, since it is directly based on diverse mathematical disciplines (number theory, abstract algebra, probability), students with less mathematical background are often intimidated and could benefit from teaching through practical examples. Analyzing the results achieved and students’ feedback, we noticed that the plain textbook-theoretical approach to teaching cryptography that we used to apply simply was not satisfactory, and subsequently decided to shift to interactive approach by introducing the open-source cryptography software CrypTool [4]. The course makeover required substantial instructor and teaching assistant efforts, especially when choosing the right examples to illustrate the most commonly used cryptography algorithms and protocols. In this paper we describe the teaching experiences and analyze students’ results which confirm that teaching cryptography interactive, through practical demonstrations, is indeed advantageous. II. RELATED WORK It is well known that cryptography is a hard-to-master discipline, which requires strong mathematical background because the security of a cryptosystem is often based on the inability to efficiently solve a problem in algebra, number theory, or combinatorics. Many instructors have made attempts to adapt their teaching methods to be flexible and to get students interested in the topic; one such approach is described in [1]. In [2], authors analyze 20 selected academic courses in cryptology with respect to their aims, scopes, contents, organization, and literature recommended to students, finally proposing the curricula tailored for different categories of students. In closely related [3], authors propose a "theory-algorithm-practice-application" teaching mode, which has proved to be efficient in achieving better teaching results, and helping students solve practical problems encountered in the engineering practice by using cryptography. III. INTERACTIVE CRYPTOGRAPHY Our cryptography course curriculum mainly follows [5] and focuses on cryptographic principles, procedures, mechanisms, and techniques required for secure communications. Fig. 1 shows the building blocks of the course. Fig. 1. Building blocks of the course 1 Saša Adamović is with the Singidunum University, Danijelova 32, 11000 Beograd, Serbia, E-mail: sadamovic@singidunum.ac.rs. 2 Irina Branović is with the Singidunum University, Danijelova 32, 11000 Beograd, Serbia, E-mail: ibranovic@singidunum.ac.rs. 3 Dejan Živković is with the Singidunum University, Danijelova 32, 11000 Beograd, Serbia, E-mail: dzivkovic@singidunum.ac.rs. 4 Violeta Tomašević is with the Singidunum University, Danijelova 32, 11000 Beograd, Serbia, E-mail: vitomasevic@singidunum.ac.rs. 5 Milan Milosavljević is with the Singidunum University, Danijelova 32, 11000 Beograd, Serbia, E-mail: mmilosavljevic@singidunum.ac.rs.