In Horizon Zero Dawn , Polyphasic entangled waveforms were an advanced encryption technology used to secure the operating system of the Chariot line of combat robots, designed and manufactured by Faro Automated Solutions.
Polyphasic entangled waveforms provided a level of OS security that was beyond military grade. Encryption protocols using polyphasic entangled waveforms were, for all intents and purposes, virtually immune from hacking, as even the most advanced supercomputer would require 50 years to brute-force a single codeset. The Chariot line's use of polyphasic entangled waveforms, as well as the complete lack of an override or backdoor into its OS, was part of Faro's insistence on the OS' adherence to what was called the Black Quartz encryption standard. Presumably this standard was the absolute strongest for encryption in terms of difficulty in hacking.
The use of polyphasic entangled waveforms to secure the Chariot robots' OS, coupled with the lack of remote access, proved to be a catastrophic decision. In the fourth quarter of 2064, one swarm of Chariot robots, owned by a corporation called the Hartz-Timor Energy Combine, experienced a glitch that caused them to stop responding to commands and become an independent entity. The swarm's robots began to replicate exponentially, utilizing their patented Biomatter Conversion technology to transform organic material, living or not, into fuel for their ever-growing numbers. As the swarm rapidly became an existential threat to all life on the planet, Faro instructed his engineers to find a backdoor in the swarm's OS, only to be reminded of his insistence on the use of polyphasic entangled waveforms, as well as his insistence that there be no semblance of a backdoor to be coded into the OS. Due to the use of polyphasic entangled waveforms as the backbone of their encryption protocols, the time required to hack the robots and obtain their deactivation codes was several orders of magnitude greater than the estimated 15 months before the swarm exterminated all life on Earth.
In the final months of life on Earth, a number of cryptographic experts were drafted into the above top-secret U.S. Robot Command operation to create a global automated terraforming system that would restore life to Earth after its eradication, known as Project Zero Dawn. Some of these experts were tasked with creating the subordinate function of GAIA, the system's central AI, known as MINERVA. MINERVA would brute-force the Faro Plague's deactivation codes and build the worldwide network of transmission towers to transmit them and shut down the robots, long after the extinction of the human species, thus paving the way for the restoration of life in the future. As estimates predicted, within approximately one and a quarter years the Faro Plague overran the planet, completely consumed the biosphere, and exterminated all life, including humans. Several decades later, MINERVA succeeded in brute-forcing and transmitting the deactivation codes, shutting down the swarm, which was the first step in restoring life to the planet.