Improved Rectangle and Linear Attacks on Lightweight Block Cipher WARP

WARP is a lightweight 128-bit block cipher with generalized Feistel structure, which can be regarded as a low-area replacement of AES-128. In this paper, we present improved rectangle and linear attacks against WARP. To optimize the cost of the key-recovery process, we propose a flexible key-guessing method for rectangle attack on WARP. Utilizing this method, we present three rectangle attacks against 27-round WARP, which improve the previous rectangle attack by one round. Considering the linear hull effect, we automatically find a 20-round linear distinguisher, and present a linear attack against 25-round WARP with the FWT-based key-recovery algorithm, which improves the previous linear attack by two rounds.