Re: [TLS] draft-ietf-tls-tls-13-17 posted

[Kazuho Oku <[e-mail]>]

Hello,

It's great to see draft-17 being published. Thank you all for the effort.

Maybe the addition of extensions field to the Certificate message got
lost in the changelog?
https://github.com/tlswg/tls13-spec/pull/654

My understanding has been that it was a post-16 change and it changes
the wire protocol.


2016-10-21 1:32 GMT+09:00 Eric Rescorla <[e-mail]>:
> Folks,
>
> I have just uploaded draft-ietf-tls-tls13-17.
>
> The major change in this draft is the removal of the 0-RTT Finished
> and resumption_context constructs and their replacement with the
> psk_binder. This has a number of side effects:
>
> - Binds in the original transcript into the resumed handshake
>   whenever resumption-PSK is used.
>
> - Provides proof of possession of the RMS by the client (subject
>   to replay issues). I've moved the obfuscated_ticket_age field
>   out of the early_data_indication so that it now provides the
>   same limited anti-replay for non-0-RTT PSK.
>
> - Removes the need for any early handshake encryption. This change,
>   along with the dual key ladders we introduced in -16, also allowed
>   us to simplify the traffic key expansion so we don't need explicit
>   labels for each key (they are already used in Derive-Secret).
>
>
> Other changes included:
> - Tweaking the PSK key exchange modes a bit (and removing the
>   inoperative ability to specify PSK auth modes, while leaving
>   a hook to do it later).
>
> - Cleaned up the cipher suite requirements for resumption and 0-RTT.
>   You can resume/do PSK as long as the PSK KDF matches, but to do 0-RTT
>   you need the whole cipher suite must match.
>
>
> This revision resolves all the outstanding technical PRs [0] and all but
> one of the non-parked technical issues (#144, whether we should remove the
> redundant TLSCipherText.opaque_type and TLSCipherText.record_version
> fields). We are pursuing measurements to resolve whether this will
> be a compat problem but we don't have them yet.
>
> As usual, comments welcome. We are already working on implementing
> -17 in NSS/Firefox and should have it before Seoul.
>
> -Ekr
>
> Full Changelog
> - Remove the 0-RTT Finished, resumption_context, and replace with a
>   psk_binder field in the PSK itself (*)
>
> - Restructure PSK key exchange negotiation modes (*)
>
> - Add max_early_data_size field to TicketEarlyDataInfo (*)
>
> - Add a 0-RTT exporter and change the transcript for the regular exporter
> (*)
>
> - Merge TicketExtensions and Extensions registry. Changes
>   ticket_early_data_info code point (*)
>
> - Replace Client.key_shares in response to HRR (*)
>
> - Remove redundant labels for traffic key derivation (*)
>
> - Harmonize requirements about cipher suite matching: for resumption you
>   need to match KDF but for 0-RTT you need whole cipher suite. This
>   allows PSKs to actually negotiate cipher suites. (*)
>
> - Explicitly allow non-offered extensions in NewSessionTicket
>
> - Explicitly allow predicting ClientFinished for NST
>
> - Clarify conditions for allowing 0-RTT with PSK
>
>
> [0] The two remaining outstanding PRs are:
> #680: Forbid post-handshake authentication except when permitted by
>       application profile. This is almost entirely a requirements-level
>       change, though it would allow clients to send "unexpected_message"
>       when receiving an unexpected CertificateRequest.
>
> #612: TLS 1.3 -> TLS 2.0
>       This has no change on the wire format.
>
>
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>



-- 
Kazuho Oku