Lightweight Design Choices for LED-like Block Ciphers

Serial matrices are a preferred choice for building diffusion layers of lightweight block ciphers as one just needs to implement the last row of such a matrix. In this work we analyze a new class of serial matrices which are the lightest possible 4 × 4 serial matrix that can be used to build diffusion layers. With this new matrix we show that block ciphers like LED can be implemented with a reduced area in hardware designs, though it has to be cycled for more iterations. Further, we suggest the usage of an alternative S-box to the standard S-box used in LED with similar cryptographic robustness, albeit having lesser area footprint. Finally, we combine these ideas in an end-end FPGA based prototype of LED. We show that with these optimizations, there is a reduction of 16% in area footprint of one round implementation of LED.