A random sequence in an innocuous GPS message field is likely encrypted traffic from the U.S. military's system for remotely updating crypto
Murdoch, a professor of security engineering and head of the Information Security Research Group at University College London, presented evidence that a 176-bit GPS sequence labelled “Subframe 4, Page 17” is encrypted material from the Pentagon’s Over-the-Air Distribution (OTAD) network, which delivers cryptographic keys to military personnel around the world. “I think the evidence that it's for key transmission—for use in distributing the keys for accessing the military GPS signals—is pretty strong now,” Murdoch said in a call with 404 Media. He noted that the military has “specialized receivers that have the ability to have keys loaded into them” and “presumably have the ability to decrypt these special messages.” In his new article, Murdoch described how this “forgotten 176-bit slot in the world’s most successful navigation signal turned out to be its quietest and most consequential broadcast.” Murdoch first spotted the sequence more than a decade ago while he was a graduate student tasked with writing a decoder for raw GPS data while working on a project funded by the European Space Agency.
5 June 2026
