Yes, this was discussed in the WG (http://trac.tools.ietf.org/wg/ipsecme/trac/ticket/104) and the idea was this:
We could have some malicious entity that could modify the offsets to ensure that the intermediaries don't parse a portion of the payload (which could contain malicious content) or inspect it differently than what it would have done otherwise. A way to protect against such attacks is to let the end node validate the WESP header by including this as a part of the ESP ICV. If the computed ICV does not match, the packet is dropped (usual IPSec processing). This does not completely eliminate the vulnerability, but it does raise the bar, because now the malicious routers would have to also position themselves both before and after the middle boxes in order to have a chance to revert the packet back to its original form before the end node verifies integrity over the packet. We have also discussed this in the Security Considerations section of the draft. We did informally speak to HW guys who are interested in implementing WESP, and they confirmed that increasing the integrity protection of ESP to now cover the WESP header is trivial. Cheers, Manav > -----Original Message----- > From: ipsec-boun...@ietf.org [mailto:ipsec-boun...@ietf.org] > On Behalf Of Jack Kohn > Sent: Tuesday, December 29, 2009 6.17 AM > To: Stephen Kent > Cc: ipsec@ietf.org; Russ Housley; i...@ietf.org; Dan McDonald > Subject: Re: [IPsec] DISCUSS: draft-ietf-ipsecme-traffic-visibility > > Are you suggesting that ESP ICV should not cover the WESP fields? > > I think, and my memory could be failing me, that this was discussed in > the WG before this got added to the draft. > > Jack > > On Tue, Dec 29, 2009 at 2:15 AM, Stephen Kent <k...@bbn.com> wrote: > > Yaron, > > > > I hate to admit it, but I lost track of the details of WESP > as it progressed > > through WG discussions and briefings at IETF meetings. When > I read the I-D > > in detail, I was very surprised to see that it was no longer a > > neatly-layered wrapper, as originally proposed. The fact > that it now calls > > for the ESP ICV to be computed in a new fashion means that > it really is > > replacing ESP, when used to mark ESP-NULL packets. > > > > From a protocol design perspective, the current version > makes no sense to > > me. Why keep the ESP header when ESP processing is now changed in a > > significant way. The WESP header cannot be processed > (completely) by > > itself, because of the dependence on the ESP ICV. So it > makes little or no > > sense to retain the ESP header in this context. I see no > strong backward > > compatibility motivation for this format, given that ESP > processing must > > change to accommodate WESP (as defined). > > > > The issue of using WESP for marking encrypted traffic is a > separate topic. I > > believe the rationale you cited was to enable WESP > extensions, but I may > > have missed other arguments put forth for this. Since most > of the WESP > > extension proposals discussed so far have proven to be > questionable, I am > > not enthusiastic about that rationale. Others have noted > that using WESP > > with encrypted traffic is not consistent with the scope of > the WG charter > > item that authorized work on WESP. Unless Pasi approves a > WESP extension WG > > item as part of re-chartering, I think it is inappropriate > to have a flag to > > mark a WESP payload as encrypted. > > > > Steve > > _______________________________________________ > > IPsec mailing list > > IPsec@ietf.org > > https://www.ietf.org/mailman/listinfo/ipsec > > > _______________________________________________ > IPsec mailing list > IPsec@ietf.org > https://www.ietf.org/mailman/listinfo/ipsec > _______________________________________________ IPsec mailing list IPsec@ietf.org https://www.ietf.org/mailman/listinfo/ipsec
