On Wednesday, 2 October 2019 22:42:32 CEST Daniel Migault wrote: > I understand the meaning of count is the higher limit of ticket and the > server can provides any tickets between 0 and count. If that is correct, > this could be clearly stated and indication to chose an appropriated value > for each cases may be provided. > > I would rather see the count value as a hard line from the server with a > MUST NOT instead of a SHOULD NOT statement.
see my previous comments: this ignores existence of post handshake authentication, ticket lifetimes and KeyUpdate > The ability to request 255 tickets with one byte can be seen as an > amplification vector, especially when a server sends directly the tickets > after its Finished message. I believe that additional text in the security > consideration could be added. true > Yours, > Daniel > > On Tue, Oct 1, 2019 at 1:27 PM Christopher Wood <c...@heapingbits.net> wrote: > > On Tue, Oct 1, 2019, at 9:15 AM, Hubert Kario wrote: > > > On Tuesday, 1 October 2019 16:01:32 CEST Christopher Wood wrote: > > > > On Tue, Oct 1, 2019, at 5:18 AM, Hubert Kario wrote: > > > > > > > ``` > > > > > > > Servers MUST NOT send more than 255 tickets to clients. > > > > > > > ``` > > > > > > > > > > > > > > per what? session? at a time? connection? > > > > > > > > > > > > This is all per session. We can state it explicitly in the next > > > > version. > > > > > > > so this count needs to be kept as part of session and impacts > > > > connections > > > > > > > that perform resumption? > > > > > > > > Sorry, I meant connection: > > > > "Clients may indicate to servers their desired number of tickets > > > > for *a > > > > > > single connection* via the following "ticket_request" extension" > > > > > > > > This is a simple hint for servers. Nothing more. No state needs to be > > > > stored > > > > > > past connection establishment. > > > > > > sounds good > > > > > > > > > > what's the expected behaviour with tickets and post-handshake > > > > > > > authentication? Are tickets sent after PHA also bound by this > > > > limit? > > > > > > > > As mentioned earlier, there is no effect, so we left it out. We're > > > > happy > > > > > > > > to > > > > > > accept text should you think it's needed. > > > > > > > > > > If the I-D states that servers should not send more tickets than the > > > > > client > > > > > asked for, and then send exactly that amount, then they won't be > > > > able to > > > > > > > send new tickets after PHA and remain compliant. > > > > > > > > > > Yes, it's completely up to the server to decide if to send tickets > > > > after > > > > > > > PHA or not, and I'm not suggesting that the client should request > > > > > for > > > > > tickets in one of its PHA messages, much less expect or require > > > > them, but > > > > > > > sending tickets after PHA is reasonable and explicitly stated > > > > behaviour: > > > > > RFC 8446 Section 4.6.1: > > > > > For instance, the server might send a new > > > > > ticket after post-handshake authentication in order to > > > > > encapsulate > > > > > the additional client authentication state. > > > > > > > > > > so the I-D should explicitly state what's the expected behaviour in > > > > that > > > > > > > case. > > > > > > > > > > IMHO, the extension should be used for the tickets sent right after > > > > the > > > > > > > handshake, it should not put an upper bound for the tickets that a > > > > server > > > > > > > can send in a single connection. For a very long lived connection > > > > > (especially if the connection uses KeyUpdate messages regularly), > > > > > the > > > > > initial tickets may expire. Server may notice that and send a new > > > > group > > > > > > > of tickets then. > > > > > > > > Since these hints are not mandatory to honor I don't think we need to > > > > describe this case. In particular, this is a valid case where ignoring > > > > the > > > > > > SHOULD is fine, in my opinion. > > > > > > > > If the draft required that servers MUST NOT send more tickets than > > > > what's > > > > > > requested, then yes, I think these details would be important. > > > > > > huh? I see the following in the draft-02: > > > Servers MUST NOT > > > send more than 255 tickets to clients. > > > > I was referring to the "SHOULD NOT send more than > > TicketRequestContents.count NewSessionTicket messages" blurb. Indeed, the > > MUST NOT above should also be a SHOULD NOT. Thanks for your patience in > > working through the kinks! > > > > > -- > > > Regards, > > > Hubert Kario > > > Senior Quality Engineer, QE BaseOS Security team > > > Web: www.cz.redhat.com > > > Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic > > > Attachments: > > > * signature.asc > > > > _______________________________________________ > > TLS mailing list > > TLS@ietf.org > > https://www.ietf.org/mailman/listinfo/tls -- Regards, Hubert Kario Senior Quality Engineer, QE BaseOS Security team Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
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