A new lightweight block cipher with involutory optimal linear diffusion

Abstract Lightweight block ciphers, with their advantages of low computational complexity and minimal storage overhead, have become a key technology to address the dual challenges of data security and resource limitations in IoT edge devices. However, due to the advancement of computing power and cryptanalysis techniques, they face severe security threats. In this case, we introduce Dawn, a lightweight block cipher with both design and implementation security. Design-wise, Dawn is the first to employ an involutory linear layer with optimal diffusion properties, enabling higher security with fewer rounds compared to existing designs. Specifically, it utilizes the lightest involutory MDS matrix on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="double-struck">F</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> to achieve local optimal diffusion. To prevent diffusion from being constrained to fixed substructures, we model the ShuffleCells operation rules and then select those that are more immune to differential and linear cryptanalysis. For the nonlinear component of Dawn, we propose an involutory structure and select one with strong cryptographic properties and that is easy to implement. Additionally, we design a two-branch key schedule for Dawn. Implementation-wise, we provide a first-order masking scheme for Dawn’s S-box to break the statistical correlation between sensitive variables and physical leakages.