SAASM
From Wikipedia, the free encyclopedia
An SAASM, for Selective Availability / Anti-Spoofing Module, 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 US military through Selective Availability.[1]
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). SAASM systems can be updated with an encrypted "Black Key" that may be transmitted over unclassified channels. All military receivers that will be newly-deployed after the end of September 2006 must use SAASM.[2]
SAASM-enabled receivers can also acquire the encrypted Y-code directly from satellite, without relying on local radio signals. This provides a substantially-increased resistance to GPS jamming, perhaps 10 to 20 db better than the PPS-SM system.
SAASM hardware modules are covered with a sophisticated anti-tampering coating, to deter analysis of their internal operation.
The next generation military signal for GPS, called M-code, will be launched on satellites beginning in 2005. A complete constellation of 18 satellites with M-code capability is planned for 2016.
[edit] References
GPSworld.com article "Saving SAASM" by Robert Huffman (Webpage, January 2006)
