Members of Cornell‘s Global Positioning System (GPS) Laboratory have cracked the pseudo random number (PRN) codes of Europe’s first global navigation satellite. The researchers published the codes and the methods used to extract them, giving free access to navigation devices that need PRNs to listen to satellites.
The navigational satellite, GIOVE-A (Galileo In-Orbit Validation Element-A), is a prototype for 30 satellites that by 2010 will compose Galileo, a $4 billion joint venture of the European Union, European Space Agency and private investors. Galileo is Europe’s answer to the US’ GPS.
GPS satellites were put into orbit by the US Department of Defense and are funded by taxpayers, so the signal is free and consumers need only purchase a receiver. Galileo, however, must make money to reimburse its investors by an as yet undecided method, but probably by charging a fee for PRN codes. Because Galileo and GPS will share frequency bandwidths, Europe and the United States signed an agreement whereby some of Galileo’s PRN codes must be “open source.” Despite broadcasting since its first signals in January 2006, none of GIOVE-A’s codes have not been made public.
In mid-January, Mark Psiaki, professor of mechanical and aerospace engineering at Cornell and co-leader of Cornell’s GPS Laboratory, requested the codes from Martin Unwin at Surrey Satellite Technology, one of three groups in the world with the PRN codes.
“In a very polite way, he said, ‘Sorry, goodbye,'” said Psiaki. Next Psiaki contacted Oliver Montenbruck, a colleague in Germany, and discovered that he also wanted the codes. “Even Europeans were being frustrated,” said Psiaki. “Then it dawned on me. Maybe we can pull these things off the air, just with an antenna and lots of signal processing.”
Within one week Psiaki’s team developed a basic algorithm to extract the codes. Two weeks later they had their first signal from the satellite, but were thrown off track because the signal’s repeat period was twice that expected. By mid-March they derived their first estimates of the code, and published final versions on their Web site on 1 April. Two days later, NovAtel, a Canadian-based major manufacturer of GPS receivers, downloaded the codes from the Web site and began tracking GIOVE-A for the first time.
Galileo eventually published PRN codes in mid-April, but they were not the codes currently used by the GIOVE-A satellite. Furthermore, the same publication labelled the open source codes as intellectual property, claiming a license is required for any commercial receiver.
Afraid that cracking the code might have been copyright infringement, Psiaki’s group sought legal advice. “We were told that cracking the encryption of creative content, like music or a movie, is illegal, but the encryption used by a navigation signal is fair game,” said Psiaki. In effect, there is no European law to copyright basic data about the physical world.
“Imagine someone builds a lighthouse,” said Psiaki. “And I’ve gone by and see how often the light flashes and measured where the coordinates are. Can the owner charge me a licensing fee for looking at the light? No. How is looking at the Galileo satellite any different?”