Re: [kitten] draft-ietf-kitten-rfc4402bis-00 (was: Re: WGLC for three "bis" documents: draft-ietf-kitten-rfc4402bis-00, draft-ietf-kitten-rfc5653bis-01, draft-ietf-kitten-rfc6112bis-00)

Benjamin Kaduk <kaduk@MIT.EDU> Wed, 18 February 2015 02:43 UTC

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Date: Tue, 17 Feb 2015 21:43:48 -0500 (EST)
From: Benjamin Kaduk <kaduk@MIT.EDU>
To: Shawn M Emery <shawn.emery@oracle.com>
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Subject: Re: [kitten] draft-ietf-kitten-rfc4402bis-00 (was: Re: WGLC for three "bis" documents: draft-ietf-kitten-rfc4402bis-00, draft-ietf-kitten-rfc5653bis-01, draft-ietf-kitten-rfc6112bis-00)
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On Mon, 16 Feb 2015, Shawn M Emery wrote:

>
> Thanks for your review, comments in-line...
>
> On 02/13/15 11:16 AM, Benjamin Kaduk wrote:
>
> > The original RFC 4402 security considerations include:
> >
> >     [...] if an
> >     application can be tricked into providing very large input octet
> >     strings and requesting very long output octet strings, then that may
> >     constitute a denial of service attack on the application; therefore,
> >     applications SHOULD place appropriate limits on the size of any input
> >     octet strings received from their peers without integrity protection.
> >
> > It is not clear to me that integrity protection is sufficient to alleviate
> > the denial of service attack, since verifying the message integrity may
> > itself consume a substantial amount of resources.
>
> I interpret this statement differently:
>
>     If integrity protection is not enforced then an attacker can construct an
> arbitrarily long string.


Woudln't the attacker be able to do that without needing a very large
input string, though?  I guess the claims it that each individual
pseudo-random() call is more expensive on a long input, so your
interpretation is still plausible.

-Ben