Producing good random numbers is a real pain in the ass. For one thing, they're never really all that random and will eventually always, after many iterations, reveal some stamp of their source via recurring patterns, probabilistic distributions, and other artifacts. Effects have causes and that's just life.
The best we can really do is make pseudo-random numbers. There are algorithms that do this pretty well, of course, but they come with a trade-off between better randomness and increasing computational effort. Chaos isn't free.
But maybe we don't always have to make our own chaos. You know what's pretty damn random? The cosmic microwave background (CMB), the dim red curtain of thermal radiation leftover from the Big Bang that permeates the universe. And according to a pair of physicists from Baylor University, Jeffrey Lee and Gerald Cleaver, this randomness might conceivably be tasked for Earth-bound random bit generation tasks, offering better encryption keys in the process.
Cleaver and Lee's CMB-based bit generator scheme is described in a letter posted to the open-access arXiv pre-print server. "The CMB power spectrum is an unpredictable, arbitrarily large, and totally random number that can be used by Alice (a sender) to generate an acceptable public- and private-key pair appropriate for use by an asymmetric key algorithm," the physicists explain.
The aforementioned power spectrum is a "unique spectra fingerprint" of the CMB that can be attained from data collected by the ESA's CMB-mapping Planck mission. It so happens that the formula used to estimate different cosmological parameters from the power spectrum—what fills in the blanks from observed data—is "uncertainty propagating" in a way that's theoretically useful for generating encryption keys.
At this point you might be wondering why an adversary (usually called Eve in the Alice and Bob encryption illustration) couldn't just do the same thing to get the same result, which could then be used to decrypt some secret message. Well, for one thing, Eve would need complete access to the stellar coordinates from which CMB power spectrum was observed, the frequency of observation, the time and duration of the observation, and more.
"However, even allowing for the possibility that Eve was privy to such specific information, the exact duplication of the Alice's random number generated from the CMB power spectrum is not possible due to random variations in photon energy at any sky frequency, spurious signals within the detectors, interference from other sources of stellar radio noise, etc," Cleaver and Lee explain. "Therefore, the digitized CMB power spectrum obtained by Alice is unique and cannot be acquired through 'identical' power spectrum observations of the CMB by Eve."
So, keys could be generated indefinitely from the same space. The main limitation is that we're talking about one-time pad keys—a message is prepared according to some protocol that the receiver has access to (and can reverse), which means that all of the space data needs to be transmitted to Bob from Alice in addition to the message. This is not perfect security by any stretch.
But, as the authors note, there's really no shortage of practically random stuff in astrophysics: planetary (non-terrestrial) radio noise, supernova remnants, radio galaxies, etc. All that's usually needed is a good radio telescope.