As I understand it, encrypted GPS (L2) does depend on key material being periodically loaded from a fill device for proper operation. The keys are rotated peri

As I understand it, encrypted GPS (L2) does depend on key material being periodically loaded from a fill device for proper operation. The keys are rotated periodically, so if somebody stole a decoder, it would only work until the key in memory expires. (Military GPS receivers also have a "zeroize" button to destroy the keys in case of imminent capture.)