Block ciphering system, using permutations to hidde the core ciphering function of each encryption round

In a system, a server provides a digital signal processing function ƒ to an executing device in an obfuscated form. The function ƒ includes a function cascade of signal processing functions ƒi, 1 i N (e.g., FC1(x)≡ƒN . . . ƒ1(x)). The server includes a processor for selecting a set of 2N invertible permutations pi, 1 i 2N; calculating a set of N functions gi, where gi is functionally equivalent to p2i−1 ƒi p2i−1, for 1 i N; and calculating a set of N−1 functions hi, where hi is functionally equivalent to p2i−1−1 p2i−2, for 2 i N. The server equips the executing device with an execution device function cascade that includes yN hN yN−1 hN−1 . . . y1, where y1, . . . , yN are function parameters (e.g., ED1(y1, . . . , yN)≡yN hN yN−1 hN−1 . . . y1), and provides the functions g1, . . . gN to the executing device. The executing device obtains the functions g1, . . . , gN and a processor for loading the execution device function cascade and applying the loaded execution device function cascade to the functions g1, . . . , gN (e.g., ED1(g1, . . . , gN)).