I-D ACTION:draft-jennings-sip-hashcash-05.txt

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	Title		: Computational Puzzles for SPAM Reduction in SIP
	Author(s)	: C. Jennings
	Filename	: draft-jennings-sip-hashcash-05.txt
	Pages		: 29
	Date		: 2007-6-4

One of the techniques used in SPAM prevention and various solutions
   for denial of service attacks is to force the SIP client requesting a
   service to perform a calculation that limits the rate and increases
   the cost of the request.  This draft defines a way to allow a UAS to
   ask the UAC to compute a computationally expensive hash based
   function and present the result to the UAS.  Although the computation
   is expensive for the UAC to compute, it is cheap for the UAS to
   verify.  The solution also allows for proxies to compute and check
   the puzzle on behalf of the UAC or UAS.

   This draft currently outlines enough information to evaluate and
   consider this approach or even run experiments.  It would need
   finalization around the forking topics discussed in the open issues
   before it would be implementable in production system.

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