Linking protection for HF radio automatic link establishment

A proposed standard has been developed by the US Federal Government to provide a degree of security to high-frequency (HF) radios implementing the automatic link establishment (ALE) protocol. As with all automated communication systems, some form of authentication is needed to validate the identity of the caller. The protection mechanism for the ALE protocol, termed linking protection (LP), provides security against ALE vulnerabilities such as unauthorized net entry and denial of access to legitimate users, and also protects the address and orderwire message information. Encryption of the ALE transmissions is based on time-varying information so that previous messages that are played back at a later time appear unintelligible to the receiver. The security offered by LP is directly related to the type of cryptographic algorithm and the length of the protection interval. The transparency of LP to the ALE protocol provides various system benefits such as establishing a link in the same amount of time as a nonprotected station and allowing a scanning receiver to acquire synchronization at any point in a transmission.<
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