Subject: [quicwg/base-drafts] Refine minimum DCID length of Initial (#2001)

From: martinduke <[email-masked]>
Date: Tue, 13 Nov 2018 14:33:12 -0800

This is meant to almost entirely mitigate #1810 by making sure that the reply to a VN packet ends up at the same server. It reduces the spurious downgrade attack signal to a corner case of a corner case.

It is much more lightweight than alternatives, if we're looking for a minimum-footprint change.
You can view, comment on, or merge this pull request online at:

  https://github.com/quicwg/base-drafts/pull/2001

-- Commit Summary --

  * Refine minimum DCID length of Initial

-- File Changes --

    M draft-ietf-quic-transport.md (5)

-- Patch Links --

https://github.com/quicwg/base-drafts/pull/2001.patch
https://github.com/quicwg/base-drafts/pull/2001.diff

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From: ianswett <[email-masked]>
Date: Tue, 13 Nov 2018 14:42:45 -0800

ianswett approved this pull request.

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From: Martin Thomson <[email-masked]>
Date: Tue, 13 Nov 2018 14:46:14 -0800

martinthomson commented on this pull request.

> @@ -1318,6 +1318,11 @@ packet is received from the server, the client MUST use the same value unless it
 abandons the connection attempt and starts a new one. The initial Destination
 Connection ID is used to determine packet protection keys for Initial packets.
 
+A client SHOULD select a Destination Connection ID length long enough to fulfill
+the minimum for every QUIC version it supports. This makes it easier to detect
+version downgrade attacks, by increasing the chance Initial packets are routed
+to the same server.

This second sentence worries me.  The mechanism we have for detecting version downgrade is robust without consistent routing.  The problem here is that it might be too robust and - during a server upgrade - the server might change its mind.  Having stable routing ensures that the server can maintain state during the cut-over and avoid connections being killed as a result.  Given the complexities involved, I would suggest that we limit this to just the first sentence.

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From: martinduke <[email-masked]>
Date: Tue, 13 Nov 2018 20:35:56 -0800

martinduke commented on this pull request.

How about eliminating the first clause, and keeping just the part about routing? A little explanation might be useful here.

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From: martinduke <[email-masked]>
Date: Tue, 13 Nov 2018 20:58:59 -0800

@martinduke pushed 1 commit.

ecd2d27  Address MT's comment?

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From: Martin Thomson <[email-masked]>
Date: Wed, 14 Nov 2018 03:32:06 -0800

martinthomson approved this pull request.

Yeah, that's better.

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From: martinduke <[email-masked]>
Date: Wed, 14 Nov 2018 11:26:20 -0800

can we merge this?

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From: Martin Thomson <[email-masked]>
Date: Wed, 14 Nov 2018 17:12:37 -0800

Merged #2001 into master.

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