TooLIP: How to Find New Instances of FiLIP Cipher with Smaller Key Size and New Filters

In this article, we propose a new tool to evaluate the security of instances of FiLIP cipher. TooLIP is user friendly, it automatically evaluates the cost of several attacks on user-defined Boolean functions. It allows to test new families of filters that are more homomorphic friendly for recent techniques of evaluations, and is designed to easily add new attacks, or change parameters in the considered attacks. To demonstrate our tool we apply it in three contexts. First we show how the keysize can be reduced for former instances with XOR-Threshold functions when the amount of encrypted plaintext obtained by the adversary is limited. Then, we use TooLIP to determine secure instances with filters in less variables for two new families of Boolean functions, leading to a more efficient evaluation and/or a reduced bandwidth. Finally, we apply it to find other instances with filters where we know only (bounds on) the algebraic immunity and resiliency.