On Thu, Jan 7, 2021 at 4:39 PM Benjamin Kaduk <ka...@mit.edu> wrote:

> On Mon, Jan 04, 2021 at 03:40:34PM -0800, Martin Duke via Datatracker
> wrote:
> > Martin Duke has entered the following ballot position for
> > draft-ietf-tls-external-psk-importer-06: Discuss
> >
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> >
> > ----------------------------------------------------------------------
> > DISCUSS:
> > ----------------------------------------------------------------------
> >
> > This is probably just my own ignorance, but I see two potential problems
> in Sec
> > 4.1.
> >
> > - 'The identity of "ipskx" as sent on the wire is ImportedIdentity,
> i.e., the
> > serialized content of ImportedIdentity is used as the  content of
> > PskIdentity.identity in the PSK extension.' IIUC ImportedIdentity has a
> maximum
> > length of 2^17 + 2. But the Identity field in the PSK option has a
> maximum
> > length of 2^16-1. I presume this never actually happens, but the spec
> should
> > handle the boundary condition, perhaps by limiting the first two fields
> of
> > Imported Identity to sum to 2^16-5 bytes or something.
>
> I'll leave this one for the authors.
>

I can see how someone would want this, but in practice that's not how it's
generally done in TLS. Trying to compute the precise upper bounds gets
complicated very fast when there are multiple fields. We do generally
try to get the lower bound right, though even then there have been
mistakes:

https://github.com/ekr/tls13-spec/pull/56/files

-Ekr
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