Further Insights on the Cryptanalysis of Lightweight Block Cipher ECLBC

ECLBC is a family of lightweight block ciphers designed especially for the Internet of Medical Things. The family contains two instances according to their block sizes, which are denoted by ECLBC-32 and ECLBC-64, respectively. ECLBC is based on SPN structure with an involutive nonlinear layer as well as an involutive linear layer. In this paper, we focus on the security of ECLBC against some attacks. Our strategy includes a direct approach and an indirect approach to make cryptanalysis of ECLBC. For differential, linear and integral attacks, we apply the attacks against SIMON to ECLBC by revealing the affine equivalent property between the two ciphers. The feasibility of such an indirect way relies on an important observation on the chosen linear layer of ECLBC, which results in a similar encryption procedure to SIMON. Thus, they have the same security against some cryptanalytic methods. We give a proof of the property in a mathematical manner and some better attacks than previous works by the designers are given. What’s more, to investigate the security of the new key schedules of ECLBC, we directly search for rotational-XOR distinguishers with different key schedules via an SAT-based method. Finally, we conclude a different result from previous works. This paper implies that ECLBC and SIMON are in a tight connection in the design and security based on the affine equivalent property. We mention that the linear layer should be noticed and carefully designed to avoid a block cipher being equivalent to existed ciphers.