Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!att!cbnews!military
From: davidb@inmet.inmet.com
Newsgroups: sci.military
Subject: Re: "Identify-Friend-or-Foe" questions
Message-ID: <12883@cbnews.ATT.COM>
Date: 8 Jan 90 05:11:16 GMT
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From: davidb@inmet.inmet.com


Taping an IFF sequence between ground and air is not sufficient.  The
theoretical algorithm (I talk from a cryptological point of view; the
extent of the implementation of this scheme is beyond my knowledge.
It may be classified) is as follows.  A random sequence of bits is
beamed from ground.  Air encrypts this and beams it back; the ground
encrypts and compares.  Identification as friend occurs if the
sequences are identical.  It is this sequence that is the root of the
"known plaintext" attack against encryption systems.

For recording to work, the broadcast would have to have been seen
previously, and the response recorded, by the ``unfriendly'' bird.