Tamper-proof GPS receivers installed in smart weapons.

• Position: Global Positioning System

Precision-guided munitions coming off the assembly line this fall will have new satellite receivers that deny access to unauthorized users. There are concerns, however, that this technology is expensive and will drive up the cost of satellite-guided weapons.

Four years ago, the Joint Chiefs of Staff mandated that all military devices relying on the Global Positioning System satellite constellation be equipped with a security chip called SAASM (selective availability anti-spoofing). The directive is scheduled to take effect on October 1. It bans military buyers from purchasing GPS receivers that are not SAASM compliant, unless they request a special waiver.

The SAASM technology was meant to ensure that receivers would not be easily compromised should they fall into enemy hands. The SAASM module replaces the existing security chips that are installed in military GPS receivers to decrypt a classified access code. Cornerstone technologies that have helped move the SAASM program forward, experts said, are advances in cryptography and the development of tamper-proof peripheries for the receiver's sensitive electronics and software.

The GPS Joint Program Office, in Los Angeles, is responsible for the implementation of the SAASM program. The National Security Agency helped the JPO set up the security architectures. Manufacturers of GPS receivers have been working on their own SAASM-compliant designs, which had to be approved both by the JPO and the NSA.

The security procedures used with current GPS receivers are based on a crypto-key architecture (black keys are unclassified, red are classified), which requires a user to have a key-code, issued by the NSA. With SAASM receivers, there will be no need for red keys, because the classification protection is embedded in the SAASM tamper-resistant coding. JPO officials predict this will simplify logistics and lower the security risks. According to one source, "the distribution of red keys is a logistical nightmare."

The SAASM module only is mandatory for new receivers. Existing systems do not have to be upgraded, unless someone chooses to do so.

Users of SPASM-based receivers can directly acquire the military P(Y) code signal from the GPS satellites. The P(Y) code has more robust anti-jamming defenses than the civilian code, which anyone can access with a commercial receiver. The SAASM, per se, doesn't provide jamming immunity. It's only a security device that enables access to the P(Y) code.

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