A processor includes an input-circuit and a Simon block cipher. The Simon block cipher includes a data transformation circuit, a constant generator, and a key expansion circuit. The data transformation circuit includes logic to shift content of data storage registers. The key expansion circuit includes logic to determine a round key based upon an input symmetric key and data input, a previous round key, and a value from the constant generator. The constant generator includes logic to output a successive one of a list of constants each clock cycle, and to store the outputted constants in storage units. The number of storage units is less than the size of the list of constants.