Subject: New [issue15] enhanced dos protection based on client puzzles

From: <[email-masked]>
Date: Mon, 19 May 2003 09:54:17 +0300

New submission from Hannes Tschofenig <[email-masked]>:

the proposed dos protection mechanism in [1] (i.e. based on 
cookies) provides the following protection: 
1) prevents against off-path adversaries (based on return-
routability)
2) prevents the paa from state creation based on an initial 
messae

particularly in environments where the adversary and the 
paa are on the same link it is difficult to provide proper 
dos protection with the help of cookies. issue (1) does not 
help since the adversary is able to see the request and the 
response. an adversary is therefore able to create a second 
message quite easily. hence the protection targeted with 
(2) might not be too helpful. 

the client puzzle concept provides a different degree of 
protection by forcing the adversary to solve a 
cryptographic puzzle. 
the concept of client puzzles is described in [2]. hip [3] 
is a protocol which uses the client puzzles to protect 
against denial of service attacks. the following text 
paragraph is taken from section 5.3.1 of [3] and describes 
the basic procedure:

"
  Responder    Generates 2 Random Numbers, I and J
                Challenge = Ltrunc(SHA1(I|J),K)
                Send I, K, and Challenge in HIP Cookie in R1
                Saves I, K, and Challenge for Delta time

   Initiator    Do Until Challenge-response = Challenge
                Challenge-response = Ltrunc(SHA1(I|Rand),K)
                EndDo
                Send I, Rand, and Challenge-response in HIP 
Cookie
                        in I2

   Responder    Match Response with Challenge based on I
                Reject if Challenge-response = Challenge
                Challenge-proof = Ltrunc(SHA1(I|Challenge-
response),K)
                Accept if Challenge-proof = Challenge

"

in pana the term paa represents the responder and the term 
pac equals the initiator of the above description.

pana can use the same concept to achieve better dos 
protection. 

according to robert moskowitz there no ipr problems with 
client puzzles (see [4]). 

- References

[1]	D. Forsberg, Y. Ohba, B. Patil, H. Tschofenig, A. 
Yegin: "Protocol for Carrying Authentication for Network 
Access (PANA)", Internet Draft, Internet Engineering Task 
Force, March, 2003.  Work in progress. 

[2] 	A. Juels and J. Brainard. Client Puzzles: A 
Cryptographic Defense Against Connection Depletion Attacks. 
In S. Kent, editor, Proceedings of NDSS '99 (Networks and 
Distributed Security Systems), pages 151-165, 1999. 

[3]	R. Moskowitz: "Host Identity Payload And Protocol", 
Internet Draft, Internet Engineering Task Force, Nov. 
2001.  Work in progress. 

[4]	HIPsec mailing list, 
http://lists.freeswan.org/pipermail/hipsec/2003-
April/000562.html, 21. April, 2003

----------
category: Technical
document: draft-ietf-pana-pana-xx.txt
messages: 29
nosy: hannes
priority: May Fix
status: No Discussion
title: enhanced dos protection based on client puzzles
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