One of the many uses of the RTL-SDR is as a random number generator for generating entropy. Entropy is needed in computing for many application such as in encryption and security.
Noel Bourke has written an article on his blog about using the RTL-SDR as an entropy source on Linux. Noel uses RTL-Entropy and shows how to set up Linux to use the RTL-SDR as the entropy source for /dev/random.
RTL-Entropy is a Linux based entropy generator which uses the RTL-SDR as the entropy source. It works by using the RTL-SDR to sample atmospheric noise and then using that noise to create randomly generated numbers.
This is useful as computers are only capable of generating pseudo-random numbers, which may look random, but are not truly random. For cryptography and security, it is desirable to use true random numbers, as pseudo-random numbers can possibly be predicted. Combining this RTL-SDR based entropy source with other entropy sources may help improve security.