Selective Vailability Anti-Spoofing Module
A Selective Availability Anti-spoofing Module (SAASM) is used by military Global Positioning System receivers to allow decryption of precision GPS coordinates, while the accuracy of civilian GPS receivers may be reduced by the United States military through Selective Availability. However, the United States Presidential Directive instructing the discontinuation of Selective Availability, along with the directive that no future GPS programs will include selective availability, makes any changes to SA unlikely. SAASM allows satellite authentication, over-the-air rekeying, and contingency recovery. Those features are not available with the similar, but older, PPS-SM system. PPS-SM systems require periodic updates with a classified "Red Key" that may only be transmitted by secure means (such as physically taking the receiver to a secure facility for rekeying or having a trusted courier deliver a paper tape with a new key to the receiver, after which that paper tape must be destroyed).