In this paper we propose Differential Fault Attack (DFA) on two Fully Homomorphic Encryption (FHE) friendly stream ciphers Rasta and$\text{FiLIP}_{\text{DSM}}$. Design criteria of Rasta rely on affine layers and nonlinear layers, whereas$\text{FiLIP}_{\text{DSM}}$relies on permutations and a nonlinear filter function. Here we show that the secret key of these two ciphers can be recovered by injecting only 1 bit fault in the initial state. Our DFA on full round (# rounds$=6$) Rasta with 219 block size requires only one block (i.e., 219 bits) of normal and faulty keystream bits. In the case of our DFA on FiLIP-430 (one instance of$\text{FiLIP}_{\text{DSM}}$), we need 30000 normal and faulty keystream bits.

In this paper, we make a comprehensive study of two classes of Boolean functions whose interest originally comes from hybrid symmetric-FHE encryption (with stream ciphers like FiLIP), but which also present much interest for general stream ciphers. The functions in these two classes are cheap and easy to implement, and they allow the resistance to all classical attacks and to their guess and determine variants as well. We determine exactly all the main cryptographic parameters (algebraic degree, resiliency order, nonlinearity, algebraic immunity) for all functions in these two classes, and we give close bounds for the others (fast algebraic immunity, the dimension of the space of annihilators of minimal degree). This is the first time that this is done for all functions in large classes of cryptographic interest.