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RE: Q: Why IPSEC to be used only in CBC mode & not other like CFB or OFB ?



ESP with null auth + AH would be fine.

I'm not convinced about the merits of AH in any case.  Given that ESP with
auth authenticates the SPI, sequence number & payload, it's not possible for
an attacker to spoof traffic through by altering the IP header.  What does
AH achieve?

Chris

> -----Original Message-----
> From: Bob Doud [mailto:bdoud@ire-ma.com]
> Sent: 07 March 2000 16:31
> To: Paul Koning; CTrobridge@baltimore.com
> Cc: ipsec@lists.tislabs.com
> Subject: RE: Q: Why IPSEC to be used only in CBC mode & not other like
> CFB or OFB ?
> 
> 
> Of course, one argument for ESP, Null Auth is when you are
> bundling it with AH.  That way, you pick up the authentication
> of the outer IP header, without duplicating the ICV's twice.
> 
> Bob
> 
> > -----Original Message-----
> > From: owner-ipsec@lists.tislabs.com
> > [mailto:owner-ipsec@lists.tislabs.com]On Behalf Of Paul Koning
> > Sent: Tuesday, March 07, 2000 10:56 AM
> > To: CTrobridge@baltimore.com
> > Cc: helger@cyber.ee; ipsec@lists.tislabs.com
> > Subject: RE: Q: Why IPSEC to be used only in CBC mode & not 
> other like
> > CFB or OFB ?
> > 
> > 
> > >>>>> "Chris" == Chris Trobridge <CTrobridge@baltimore.com> writes:
> > 
> >  Chris> It does reinforce the advantages of authentication 
> in ESP.  I
> >  Chris> don't know if I've come to the point of assuming ESP
> >  Chris> authentication is pretty much essential through 
> this group or
> >  Chris> though discussions with customers, but what do others think?
> > 
> > I've been convinced by Steve Bellovin's papers that it is essential.
> > Unfortunately, we're not currently allowed to reject ESP with null
> > authenticaton.  As far as I'm concerned, that's a bug, but
> > unfortunately some feel differently.  We're definitely 
> telling people
> > in documentation not to skip authentication.
> > 
> > Both in software and hardware, there is no performance justification
> > for omitting authentication.
> > 
> > 	paul
> > 
> > 
>