Re: [TLS] implementation of cookies in DTLS
Eric Rescorla <ekr@rtfm.com> Tue, 15 March 2011 11:51 UTC
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Date: Tue, 15 Mar 2011 04:52:45 -0700
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From: Eric Rescorla <ekr@rtfm.com>
To: Nikos Mavrogiannopoulos <nmav@gnutls.org>
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Subject: Re: [TLS] implementation of cookies in DTLS
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On Tue, Mar 15, 2011 at 4:37 AM, Nikos Mavrogiannopoulos <nmav@gnutls.org> wrote: > On Tue, Mar 15, 2011 at 12:18 PM, Eric Rescorla <ekr@rtfm.com> wrote: > >>> 2. Drop requirement: The server MUST use the same >>> version number in the HelloVerifyRequest that it would use when >>> sending a ServerHello. Upon receipt of the ServerHello, the client >>> MUST verify that the server version values match. >>> This will create incompatibilities when more than 1 DTLS protocols are >>> implemented >>> in a single client or server. It is not really possible for a server >>> to do an emulation of >>> the decisions it would do as if a state existed. What are the reasons for this >>> requirement? >> I don't understand why this is an issue: the server can remember what the >> client offered (indeed, he must remember a whole pile of other stuff in order >> to verify that it hasn't changed) by stuffing a digest into the cookie. > > My issue is not about server remembering stuff, but the fact that at this point > the server has minimum information and has to do actual negotiation of the > protocol version. > > Depending on the implementation chosing the version to negotiate might not > be simple. I.e. the application might have configured that DTLS 1.0 and DTLS > 1.2 are allowed, but say for example only ciphersuite 0xfb, 0xbf is enabled for > this client, that has the constraint that it can be used with DTLS 1.0 > (probably > this is not an issue now in DTLS but this scenario is common in TLS). > Thus the server cannot readily negotiate the highest DTLS 1.2, but has to also > check ciphersuites for conflicts, meaning that this pre-handshake cannot really > be kept as minimal as possible. > > I think the pre-handshake should be as dumb as possible to serve its > role as DoS > protection and no more. In typical cases it is expected to be implemented as > something external to the handshake process, thus would be nice to require > as less information and information interpreting as possible. Ah, I see your point. I'll have to think a bit about what I think the best approach is here. -Ekr
- Re: [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- Re: [TLS] implementation of cookies in DTLS Robin Seggelmann
- Re: [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- Re: [TLS] implementation of cookies in DTLS Robin Seggelmann
- Re: [TLS] implementation of cookies in DTLS Robin Seggelmann
- Re: [TLS] implementation of cookies in DTLS Michael Tüxen
- Re: [TLS] implementation of cookies in DTLS Robin Seggelmann
- Re: [TLS] implementation of cookies in DTLS Michael Tüxen
- Re: [TLS] implementation of cookies in DTLS Robin Seggelmann
- Re: [TLS] implementation of cookies in DTLS Michael Tüxen
- Re: [TLS] implementation of cookies in DTLS Eric Rescorla
- Re: [TLS] implementation of cookies in DTLS Michael Tüxen
- Re: [TLS] implementation of cookies in DTLS Eric Rescorla
- Re: [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- Re: [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- Re: [TLS] implementation of cookies in DTLS Eric Rescorla
- Re: [TLS] implementation of cookies in DTLS Nikos Mavrogiannopoulos
- Re: [TLS] implementation of cookies in DTLS Michael Tüxen
- Re: [TLS] implementation of cookies in DTLS Eric Rescorla