A system including a pseudo-random number generator having a register to store an extended state having a reduced state and a dynamic constant, an initialization module to initialize a part of the extended state based on a Key and/or an Initial Value, a state update module to update the reduced state, an output word module to generate output words, the state update module and the output word module being adapted to operate through cyclical rounds, each round including updating the reduced state and then generating one of the output words, and an update dynamic constant module to update the dynamic constant, wherein in a majority of the rounds, updating of the reduced state and/or generation of the output word is based on the dynamic constant, and the dynamic constant is only updated in a minority of the rounds. Related apparatus and method are also described.