Committing Security Analysis of SMAC

SMAC is a newly proposed MAC family built based on the finite state machine (FSM) of the SNOW-V series, targeting the high speed requirements in 5G and beyond. In this paper, we study the committing security of the SMAC family. We first theoretically reduce the committing security of SMAC to the properties of the underlying components, including the Davies-Meyer construction and the compress function. We then propose practical key-committing attacks against SMAC-1, SMAC-3/4, and SMAC- 1 × n , as well as a theoretical attack against SMAC-1/2 with complexity far below the birthday bound. To enhance the committing security of SMAC, we further suggest two variants of SMAC that can resist our attacks. Our results shed some light on how to design highly efficient MACs with robust committing security.