Enhancing SPN ciphers: Dynamic substitution-key addition layers via binary block circulant matrices

The SPN (Substitution-Permutation Network) block cipher is one of the fundamental and important structures in the field of symmetric encryption, widely used in modern encryption algorithms such as AES. Due to its ability to efficiently diffuse and obscure data, SPN plays a key role in building secure and reliable encryption systems. However, with the development of the SPN block cipher, many studies have been conducted to identify cryptanalytic attack methods to break this cipher. To enhance the security of the SPN block cipher, recent research has focused on dynamic transformations of its components and often relies on the secret component, the key. In this study, we propose a new method that combines the dynamicization of two key components: the substitution layer and the key addition layer of the SPN block cipher. This method is based on using a binary block circular shift matrix, formed by combining a binary circular shift matrix with a binary Hadamard matrix. Our algorithm only requires the use of 26 additional key bits but can generate up to 228 key-dependent S-boxes with strong cryptographic properties and 233 key-dependent XOR tables. When applying these key-dependent S-boxes and XOR tables to dynamically modify the AES block cipher, it can increase the security level of the dynamic AES block cipher by 233 compared to AES