Security Evaluation of LIGHTMAC: Second Preimage Attack using Existential Forgery

Message Authentication Code (MAC) is a cryptographic hash function that uses the cryptographic key(s) to generate a MAC value or a tag. MAC security property that must be satisfied is the second preimage resistance; given an input, it is difficult to find different inputs with the same tag. A lightweight MAC called LIGHTMAC was introduced in 2016 by Luykx et al. The scheme uses lightweight block cipher as its encryption function. This paper discusses the application of a second preimage attack on the LIGHTMAC scheme using existential forgery methods. The purpose of this attack is to determine the resistance of LIGHTMAC's second preimage property. From observation and experiments with instantiation using SIMECK32/64, it is found that the attack is more efficient than brute force attacks with birthday attack complexity. Furthermore, a modification is recommended to avoid the second preimage attack on LIGHTMAC.