Abstract:

Cryptography is the process of encrypting, i.e., hiding or coding, information so that only the intended recipients can decrypt, i.e., read, them. To this aim, particular methods, i.e., algorithms are devised and used for transforming readable data (plaintext) into an unreadable format (ciphertext) so that unauthorized access and tampering are prevented. Cryptographic algorithms play essential and pivotal role in our current highly interconnected, network centric world since they form a key element of secure digital communication and modern online economies.

Cryptographic algorithms rely on mathematical concepts and use secret keys for data encryption and decryption. AES (Advanced Encryption Standard) is a highly secure, symmetric encryption algorithm used globally to protect sensitive digital data by transforming it into unreadable code, using the same key for encryption and decryption. It is a NIST standard, supporting 128, 192, or 256-bit keys, and is a cornerstone for security from online banking to file storage. It is commonly used in Wi-Fi security protocols, to encrypt data transmitted over wireless networks. AES encrypts data in fixed-size blocks (128 bits) through multiple rounds of transformations. Each round involves several steps like substituting data, shifting rows, mixing columns and adding a part of the key. AES-256, which has a key length of 256 bits, is considered practically unbreakable by brute force with current computing power, making it one of the most secure encryption systems in use today.

AES is included in the curriculum of Cryptography courses in higher education. However, AES is considered difficult to teach primarily because it moves toward a complex mathematical structure involving finite field arithmetic (including XOR and polynomial multiplication), matrix multiplication and non-linear byte transformations requiring students to understand both high-level cryptographic goals and low-level byte-level arithmetic simultaneously. Consequently, teaching AES often focuses on presenting general concepts rather than deep-diving into the math and on individual round functions rather than the entire 10-round process.

Motivated by these observations and with an intention to make the AES algorithm easier for students to understand and use, we designed and implemented an online application which enables students to familiarize with the underlying math and the entire 10-round process of AES. Our application includes learning and training sections as well as section for forward and inverse S-box (Substitution box), a fixed lookup table used in AES during the encryption and decryption processes.It also provides a calculator particularly designed for performing XOR operations and conversions involving hexadecimal and binary numbers, which are extensively used in AES. Within the educational section, step-by-step execution of the complete AES process can be performed for all AES key-sizes for both encryption and decryption including visualization and detailed information for all applied transformations. The training section enables users to practice each step of the AES algorithm in an interactive manner with guidance provided along the way. To the best of our knowledge, no similar application has been presented so far.

Our application, currently available in greek and english, has been developed using the React open-source JavaScript library as the main development ecosystem and Github Pages for online hosting.

Keywords:

Cryptography courses, AES encryption/decryption algorithm, learning and training web app, visualization of the 10-round transformation process, interactive forward and inverse S-box, XOR calculator, React, Github.