1. A method for designing a circuit suitable for generating random bits, wherein the circuit comprises a number m of mapping devices, wherein each of the mapping devices is supplied a number n of input bits, where n is a value greater than 1, and wherein each of the mapping devices uses a respective function to carry out a bijective mapping of the n input bits to n output bits, the method comprising: (a) selecting a j-th mapping device from a first of the mapping devices to the m-th mapping device and prescribing a j-th specific function from a set of bijective mappings as the j-th function, wherein a j-th concatenation of the j functions carries out a j-th fixed-point-free mapping when the j-th specific function is prescribed as the j-th function; applying, by the j-th concatenation, the j functions in an ascending order starting with the first function; selecting at least one i-th mapping device from the first mapping device to the m-th mapping device, where i is not equal to j, and prescribing an i-th specific function from a set of bijective mappings as the i-th function, wherein an i-th concatenation of the i functions carries out an i-th fixed-point-free mapping when the i-th specific function is prescribed as the i-th function; and applying, by the i-th concatenation, the i functions in an ascending order starting with the first function.