An electronic apparatus includes a permutation circuit and an arbitration circuit. The permutation circuit is configured to apply to an input vector a permutation selected from a plurality of predefined permutations in response to a control word. The arbitration circuit is configured to receive a vector of requests for a resource, to instruct the permutation circuit to apply a randomly-selected permutation to the vector of requests, by configuring the permutation circuit with a corresponding randomly-selected control word so as to produce a permuted vector, to select an element of the permuted vector, to apply to the permuted vector an inverse of the randomly-selected permutation so as to produce an inversely-permuted vector, to identify an element of the inversely-permuted vector to which the selected element of the permuted vector is mapped, and to assign the resource to a client corresponding to the identified element of the inversely-permuted vector.