NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Is Celestial Navigation really a backup to GPS Navigation?
From: Brad Morris
Date: 2018 Sep 19, 14:59 -0400
From: Brad Morris
Date: 2018 Sep 19, 14:59 -0400
Hi Paul
I read accounts in the past wherein PLGRs were seized from militaria collections, by government officials. I simply presumed that this practice continued to date. Apparently it does continue for the DAGR, according to some, but not the PLGR.
I had occasion to compare the output of a keyed PLGR to a civilian Garmin GPSMAP76. The PLGR produced the same geographic location, albeit at a slightly longer time for first fix than the Garmin. The PLGR was at all times in the possession of the armed forces member, I got a play with it, not ownership. Seemed a little clunky, to be honest.
Thanks for explaining that "neutering" really means "no key" to access the L2 encrypted military channel. That makes perfect sense. That's also going to make the military channel super hard to spoof. No key means no spoof. Still can try to jam it, but not spoof it.
Brad
On Wed, Sep 19, 2018, 7:54 AM Paul Hirose <NoReply_Hirose@fer3.com> wrote:
On 2018-09-18 5:45, Brad Morris wrote: > I'll correct myself on the government seizure part. Apparently you can buy > older, somehow neutered units and the government doesn't come after you > (anymore). The great strength of a military GPS receiver is access to encrypted signals radiated by the satellites. These provide enhanced accuracy and resistance to jamming and spoofing. But you can't unlock this capability unless the receiver is loaded with the current cryptographic key. During my USAF days one of my duties was the preflight loading of keys for secure voice radios, IFF Mode 4, and GPS. These keys were all different, and I was always a little stressed making sure they were the correct ones for the time of the flight. Cipher changes (old replaced by new) were in terms of UTC, so the offset from local time had to be kept in mind. Also, there were different conventions for specifying the time. One cipher was designated by its expiration time, another by the time it became valid. That was second nature to the specialists who had been trained from scratch in this field, but I wasn't one of those and had to always think it through carefully. The crypto safe contained keys for several days in advance. It was easy to grab the wrong one. Ciphers were stored in KYK-13 key transfer devices. A "kick thirteen" was about the size and shape of a bar of soap and could hold six keys. To key the GPS, connect the KYK-13 to the GPS receptacle in the cockpit, set the 1 - 6 selector to the register that contains the correct key, turn it on, and watch for the flash of the red light. Turn off the KYK-13, disconnect, and you're done. It takes only a few seconds. I never had occasion to load a hand held receiver such as a PLGR, but I suspect the method is almost the same. http://www.cryptomuseum.com/crypto/usa/kyk13/index.htm
