Re: 6MAN WG Last Call: draft-ietf-6man-predictable-fragment-id-01

[神明達哉 <[e-mail]>]

At Tue, 09 Dec 2014 06:22:49 -0300,
Fernando Gont <[e-mail]> wrote:

> > - Section 4:
> >
> >    The Identification value of the Fragment Header MUST NOT be
> >    predictable by an off-path attacker.
> >
> >   'MUST NOT be predictable' sounds vague to me, especially with the
> >   RFC2119 keyword.  I'm not sure if there's a precedent of the use of
> >   this word with a normative keyword, but even if there's, I would
> >   personally still like to see a clearer term here.
>
> FWIW, RFC6056 (port randomization) says:
>
>    Ephemeral port selection algorithms SHOULD obfuscate the selection of
>    their ephemeral ports, since this helps to mitigate a number of
>    attacks that depend on the attacker's ability to guess or know the
>    five-tuple that identifies the transport-protocol instance to be
>    attacked.
>
>
> OTOH, RFC6528 (TCP SEQ randomization) says:
>
>    F() MUST NOT be computable from
>    the outside, or an attacker could still guess at sequence numbers
>    from the ISN used for some other connection.
>
> where F() is essentially the TCP SEQ generator..

By referring to these, do you mean you think the current text of the
draft is good enough? (asking simply because I'm not sure about the
intent).

--
JINMEI, Tatuya