Re: [OAUTH-WG] Question lengths in draft-sakimura-oauth-tcse-03

[Brian Campbell <[e-mail]>]

I'd say it should be a MUST so that implementations are consistent about it.


On Fri, May 16, 2014 at 3:27 PM, Bill Mills <[e-mail]> wrote:

> The HTTP specs don't limit these things, but implementations do, and the
> problems when you run into them are a rea pain.
>
> DO we want to make this a hard limit, or should it be guidance in the form
> of RECOMMENDED or SHOULD?
>
>   On Friday, May 16, 2014 9:35 AM, Brian Campbell <
> [e-mail]> wrote:
>   Yeah, I agree with John here. There are a few good reasons to restrict
> the length of the code_challenge. One is trying to keep the authorization
> request URI to reasonable size as it will eventually run into various
> limits on clients and/or servers. The other is constraining the amount of
> data that an AS needs to store per code.
>
>
>
>
> On Fri, May 16, 2014 at 7:41 AM, John Bradley <[e-mail]> wrote:
>
> From the AS side you probably want to know what the max size you need to
> store per code.
>
> On the call to the token endpoint it is a POST so size should not be an
> issue.
>
>
> On May 16, 2014, at 3:10 PM, Nat Sakimura <[e-mail]> wrote:
>
> Now that I cannot remember what limit we were hitting, it might be a good
> idea to remove the constraint and see if anyone protests.
>
> What do you think?
>
> Nat
>
>
> 2014-05-14 20:46 GMT+09:00 Brian Campbell <[e-mail]>:
>
> That too would suggest that the length limit be on code_challenge because
> that's the parameter that will be on URIs getting passed around. The
> code_verifier is sent directly in the POST body from client to AS.
>
>
> On Tue, May 13, 2014 at 12:52 AM, Nat Sakimura <[e-mail]> wrote:
>
> +1 for octet. We used to have "bytes" in JW* so I used "bytes" here, while
> at the same time complaining in Jose that it should be "octet". JW* changed
> to "octet" but I failed to sync with it in the last few edits.
>
> I do not quite remember which platform, but the reason for the limit was
> that some platform had some limitations as to the length of the sting to be
> passed to it through URI and we did not want the challenges to be truncated
> by that limit.
>
> Best,
>
> Nat
>
>
> 2014-05-13 6:56 GMT+09:00 Brian Campbell <[e-mail]>:
>
> And it'd give the AS some direct guidance on protecting itself from crazy
> long code_challenge values rather than relying on the client not to do
> something creative.
>
>
> On Mon, May 12, 2014 at 3:54 PM, Brian Campbell <
> [e-mail]> wrote:
>
> Right but that's why I'm asking why not just put the limit on
> code_challange rather than inferring it from code_verifyer + challenge
> algorithm, which probably bounds it but doesn't necessarily do so? It's not
> a big deal but would read more clearly, I think.
>
>
> On Mon, May 12, 2014 at 3:48 PM, John Bradley <[e-mail]> wrote:
>
> I think octets is more consistent with other JW* and OAuth specs.
>
> The code_challange is the same length as the code_verifyer or is a hash of
> the code_verifyer so likely smaller than 128octets (43 ish for base64 256
> bit)
>
> Limiting the code_verifyer size sets the upper bound for code_challange,
> unless someone comes up with a really creative code challenge algorithm.
>
> I will talk to nat about changing it to octets when I see him tomorrow.
>
> John B.
>
> On May 12, 2014, at 11:15 PM, Derek Atkins <[e-mail]> wrote:
>
> > Brian Campbell <[e-mail]> writes:
> >
> >> I notice that code_verifier is defined as "high entropy cryptographic
> random
> >> string of length less than 128 bytes"  [1], which brought a few
> questions and
> >> comments to mind. So here goes:
> >>
> >> Talking about the length of a string in terms of bytes is always
> potentially
> >> confusing. Maybe characters would be an easier unit for people like me
> to wrap
> >> their little brains around?
> >
> > It depends if it really is characters or bytes.  For example there are
> > many multi-byte UTF-8 characters, so if it really is bytes then saying
> > characters is wrong because it could overflow.  So let's make sure we
> > know what we're talking about.  Historically, if we're talking bytes the
> > IETF often uses the phrase "octets".  Would that be less confusing?
> >
> >> Why are we putting a length restriction on the code_verifier anyway? It
> seems
> >> like it'd be more appropriate to restrict the length of the
> code_challenge
> >> because that's the thing the AS will have to maintain somehow (store in
> a DB
> >> or memory or encrypt into the code). Am I missing something here?
> >>
> >> Let me also say that I hadn't looked at this document since its early
> days in
> >> draft -00 or -01 last summer but I like the changes and how it's been
> kept
> >> pretty simple for the common use-case while still allowing for crypto
> agility/
> >> extension. Nice work!
> >>
> >> [1] http://tools.ietf.org/html/draft-sakimura-oauth-tcse-03#section-3.3
> >
> > -derek
> >
> >> _______________________________________________
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> >
> > --
> >       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
> >       Member, MIT Student Information Processing Board  (SIPB)
> >       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
> >       [e-mail]                        PGP key available
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>
>
>
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> Nat Sakimura (=nat)
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> @_nat_en
>
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> --
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