An Overview of Common Post-Processing Methods in Random Number Generators with an Emphasis on Use in Renewable Systems

One of the main components in the security of cryptography systems is random numbers. Random numbers are often used in the generation of secure keys, digital signatures, and other cryptographic systems. Random numbers generated by an algorithm are called pseudo-random numbers. Although pseudo-random numbers have good statistical properties, they have the problem of periodicity. For this reason, to generate random numbers, the true random number generator method is used, which uses a physical entropy source to generate random numbers. In the real random number generator method, due to the instability of electric circuits, a post-processing step is needed so that the generated numbers have acceptable statistical characteristics. In this paper, an overview of the common post-processing methods of random number generators has been done, so that some of the introduced methods are also used in the generation of quantum random numbers. An important point is the role of renewable energies in the design and construction of devices with limited computing power. For this purpose, in the final part of this article, a fast and optimal post-processing method is introduced in terms of hardware implementation, which can be used in mobile phones, smart cards and devices that have limited computing power.