Dear all,
Thank you for your interest in this work !
I would tend to agree with Lucas and think we should consider scenarios
where BDP frames would be used with TLS resumption and I do not see the
need for proposing another trust mechanism; But there may be scenarios I
do not see ?
More comments inline.
Kind regards,
Nico
On 11/3/23 16:44, Lucas Pardue wrote:
Hi folks,
I'm still trying to come up to speed on this spec. But when I've
thought about it a little, its seemed very natural to associate the
BDP frame (contents) with the TLS session. We already have a lot of
text about TLS session resumption in QUIC. It feels like there is
already a template design with HTTP/3 - a server sends SETTINGS to
tell a client something unique about the active QUIC connection. RFC
9114 section 7.2.4.2 [1]states
> When a 0-RTT QUIC connection is being used, the initial value of
each server setting is the value used in the previous session.
ClientsSHOULDstore the settings the server provided in the HTTP/3
connection where resumption information was provided, but theyMAYopt
not to store settings in certain cases (e.g., if the session ticket is
received before the SETTINGS frame). A clientMUSTcomply with stored
settings -- or default values if no values are stored -- when
attempting 0-RTT. Once a server has provided new settings,
clientsMUSTcomply with those values.¶
<https://www.rfc-editor.org/rfc/rfc9114.html#section-7.2.4.2-6>
So with a bit of massaging, if we can link BDP frame to session
resumption. we know that it is based on a previous trust relationship.
Is there any scenario where BDP frame would want to be used without
TLS resumption?
[NK] I agree.
Cheers
Lucas
[1] - https://www.rfc-editor.org/rfc/rfc9114.html#section-7.2.4.2-6
On Thu, Nov 2, 2023 at 6:17 PM Gorry Fairhurst <[email protected]>
wrote:
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.
[NK] If the draft is not clear enough on these relevant questions, we
ought to make things clearer.
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?
[NK] The client should not be able to transmit unauthenticated CC
parameters that are not checked / known by the server. In the current
spec, the client can only send data previously received by the server.
Malicious clients could try to cause a DoS on the server but that would
not be specific to BDP Frame but to 0-RTT in general.
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.
[NK] We may not specify how to compute the secure hash but that could be
interesting discussions if you think the draft needs to be more specific
on this. IMHO the client does not need to know how the secure hash is
compute and thus not sure we need interoperability.
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.
:-)
[NK] Do we need to specify this in the draft or should this be let to
implementers to define the most relevant approach (w.r.t. frame
scheduling to format QUIC packets).
Looking forward to hearing your thoughts.
[NK] Thank you for your comments !
Cheers,
Q Misell
Gorry
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