Re: Authentication in draft-kuhn-quic-bdpframe-extension

[Gorry Fairhurst <[e-mail]>]

On 02/11/2023 16:43, Q Misell wrote:
> Hi all,
>
> I've been working with Gorry (and others) on actually implementing the 
> BDP frame extension, and further refining the draft based on 
> experience from implementation.
Q, I think I can help a little, see below, but I think there are good 
questions here.
>
> One thing that came up that I'd like to ask the WG's opinion on is 
> that of authentication of the BDP frame, and when it should be sent in 
> the exchange. I've had a few thoughts on this, it'd be great to hear 
> what others think of them, or what other suggestions people might have.
>
> First, my thoughts on authentication. Do the CC parameters need to be 
> authenticated at all? I would say "yes" as a client sending some 
> unauthenticated CC parameters could cause a DoS of the server (or any 
> other node along the path) by trying to send far too much data at once.
The reason for the secure hash around the contents of the BDP Frame is 
to allow a server to know the CC params had not been modified. Of course 
you caould ask what sort of information contributes to that hash, to 
make the server confident that it can accept CC params from the client 
and believe that these have not been modifed? That could be important?
> Should the CC parameters be encrypted? Probably not, as a client which 
> is aware of a major decrease in available capacity could compare the 
> new link capacity to its stored CC parameters and decide not to send 
> them. If they're encrypted the client can't inspect what CC parameters 
> the server thinks the link will have.

Perhaps the ID ought to be clearer. The QUIC Session is of course 
encrypted and authenticated, so, in this respect, the BDP Frame is 
protected in transit along the path using TLS.

The current proposal is not to additionally encrypt the CC params 
*within* the BDP, so that a client could read these and utlise as it 
sees fit. This still needs to authenticate the entire set of params, so 
that the server could trust them.

The params include an endpoint token used by a server  to represent the 
remote endpoint - we could have used the client IP source address for 
this if the client had an invariant public IP source address. That's not 
so common with IPv6 or the use of IPv4 NAPT - so the server has to find 
a way to represent it's view of the client as the endpoint token. There 
could be possibilities to do this quite differently.

>
> How should they be authenticated? There are a few options I can see 
> here, and I'm unsure which is best:
> (1) Authenticated with the TLS certificate
> (2) Authenticated with some other asymmetric key
> (3) Authenticated using some symmetric key known only to the server
> (4) Same as 3 but with a key identifier
>
> Options 1 and 2 allow the client to verify the authentication over the 
> CC parameters, but this doesn't seem to be of much use to me. Option 1 
> additionally sets a time limit on use of stored CC parameters, as the 
> TLS certificate will eventually expire. This doesn't seem to me to be 
> much of an issue. A new connection far into the future (say 1-2 
> months) would almost certainly have different CC parameters anyway.
>
> Option 3 seems the best to me. It would allow one key to be shared 
> across an array of anycast servers, without sharing other keying 
> material that might be used to protect more sensitive parts of the 
> connection. Option 4 additionally expands on this by allowing key 
> rotation without immediately invalidating all current stored CC 
> parameters.
So, if this is about how to construct the secure hash, irt seems like an 
interesting topic to find out more, I'd agree.
>
> When should the BDP frame be sent? There are two places I can see BDP 
> frames being useful to send:
> (1) After initial frames but before crypto frames
> (2) After crypto frames and before application data
>
> Option 1 allows for the previously calculated CC parameters to be used 
> for the sometimes quite large TLS handshake, but also precludes 
> options 1 and 2 for authentication. Option 2 allows for greater 
> flexibility in authentication, and also makes the BDP frame encrypted 
> in transit. I'm unsure what the privacy implications of an unencrypted 
> BDP frame are, so if anyone can come up with a reason CC data 
> shouldn't be observable to an intermediary that would be greatly 
> appreciated.
:-)
>
> Looking forward to hearing your thoughts.
> Cheers,
> Q Misell
Gorry
> ------------------------------------------------------------------------
>
> Any statements contained in this email are personal to the author and 
> are not necessarily the statements of the company unless specifically 
> stated. AS207960 Cyfyngedig, having a registered office at 13 
> Pen-y-lan Terrace, Caerdydd, Cymru, CF23 9EU, trading as Glauca 
> Digital, is a company registered in Wales under № 12417574 
> <https://find-and-update.company-information.service.gov.uk/company/12417574>, 
> LEI 875500FXNCJPAPF3PD10. ICO register №: ZA782876 
> <https://ico.org.uk/ESDWebPages/Entry/ZA782876>. UK VAT №: 
> GB378323867. EU VAT №: EU372013983. Turkish VAT №: 0861333524. South 
> Korean VAT №: 522-80-03080. AS207960 Ewrop OÜ, having a registered 
> office at Lääne-Viru maakond, Tapa vald, Porkuni küla, Lossi tn 1, 
> 46001, trading as Glauca Digital, is a company registered in Estonia 
> under № 16755226. Estonian VAT №: EE102625532. Glauca Digital and the 
> Glauca logo are registered trademarks in the UK, under № UK00003718474 
> and № UK00003718468, respectively.
>