Block Ciphering System, Using Permutations to Hide the Core Ciphering Function of Each Encryption Round

摘要

In a system ( 600 ), a server ( 610 ) provides a digital signal processing function f to an executing device ( 620 ) in an obfuscated form. The function f includes a function cascade of signal processing functions f₁, 1<=i<=N to formula (I). The server includes a processor ( 612 ) for selecting a set of 2N invertible permutations p_i, 1<=i<=2N; calculating a set of N functions g, where g, is functionally equivalent to formula (II) for 1<=i<=; and calculating a set of N-1 functions h, where h, is functionally equivalent to formula (III) for 2<=i<=N. The server includes means ( 614 ) for equipping the executing device with an execution device function cascade that includes formula (IV), where y₁, . . . , y_N are function parameters to formula (V), and means ( 616 ) for providing the functions g₁, . . . g_N to the executing device. The executing device includes means ( 626 ) for obtaining the functions g₁, . . . , g_N and a processor ( 622 ) for loading the execution device function cascade and applying the loaded execution device function cascade to the functions g₁, . . . , g_N(e.g., ED,(g₁, . . . , g_N)).