The two biggest challenge using GPS precise time in critical applications is that so many things can corrupt the signal after it leaves the satellite and before it gets to the user.
At the National PNT Advisory Board meeting on the 28th of June, iPosi and UrsaNav gave a thought provoking presentation on how combining GPS and eLoran with an additional message in the signal could solve that. They claim that it would provide “traceable, tamper-proof” time. They are so confident that they have apparently trademarked the phrase “Trusted Time.”
This could be a major cyber-security advance as it could virtually eliminate denial of service and deception for both time and location.