The described cipher system includes a bits of some randomness (BOSR) reservoir; a first multiplexer circuit that receives a BOSR key, a functional key, and a first control signal for selection between the BOSR key and the functional key; a second multiplexer circuit that receives a BOSR state, a functional state, and a second control signal for selection between the BOSR state and the functional state; a block cipher logic circuit that receives the outputs from the first and second multiplexer circuits and a functional input. The block cipher outputs bits into either the BOSR reservoir or as a functional output according to a third control signal. The cipher system includes a control logic block that outputs the first control signal, second control signal, and third control signal and controls whether a clock cycle of the block cipher logic circuit is used for a BOSR operation or a functional operation.