On the afternoon of June 14, 2020, the Honors College invited Mr. Wang Qichun, Professor of School of Computer Science and Technology at Nanjing Normal University and the head of the master's degree of first-level discipline in cyberspace security, to give a lecture on the topic of "Talking about Cryptography" to the college students.

At the beginning of the event, Prof. Wang Qichun introduced the concept of cryptography, starting from a series of shifting passwords during the time of Julius Caesar. He introduced the communication and basic terminology of the secrecy model, and the terms "plaintext", "ciphertext", "encryption" and "decryption" in turn.

The presentation was followed by an analysis of the research objects of cryptography and a discussion of the types of cryptographic algorithms: symmetric ciphers are divided into "stream ciphers" and "packet ciphers", asymmetric cipher is also known as "public key cipher", hash function is used to calculate message digest… These terms are short and profound, and provide a glimpse into the nature of the cryptography field. On the basis of this, Professor Wang presented each of the above and gave the relevant model diagrams and the mathematical principles implied in them. For example, LFSR cryptanalysis obtains target results by matrix operations, the nonlinear component involves the use of n-element Boolean functions, RSA algorithm combined with the knowledge of number theory carries on the encryption and decryption... Then, Professor Wang also talked about the emerging concept of "blockchain", analyzing its strengths and constructive levels, which are shown to be stable and reliable.

At the end of the lecture, Professor Wang gave an introduction to the disciplines involved in cryptography and the world's top cryptography schools, and showed the supervised students' achievements at international conferences. Returning to the original Caesar code, Professor Wang used the phrase "it's the best day ever to be with you" as a riddle and encouraged the students to study cryptography and discover fun and success in research.

After the lecture, the students thought deeply and discussed actively, which was very rewarding. The lecture stimulated students' interest in the field of computer science. Rigorous study, good use of the literature and willingness to think were the themes conveyed by the activity; pioneering and innovation, pursuit of excellence and breakthroughs were the great expectations given to the college students by the activity!