A feedback and shift unit is arranged to reduce to a minimum the number of processing steps required in a processor, such as a DSP, to achieve a particular operating function, such as a linear feedback shift or a stepping function used by encryption algorithms. The feedback and shift unit (50) comprises a linear feedback shift register (52) for storing a value of the feedback and shift unit. A tap register (56) stores a tap position indicator indicative of tap positions for the feedback and shift unit (50). An input provides data to the feedback and shift unit. A feedback matrix, coupled to receive the data from the input, provides data bits, generated in response to the data and the tap position indicator, that are shifted into the linear feedback shift register (52) to form the value stored therein.