Re: [quicwg/base-drafts] Which DCID determines Initial keys (#3862)

Martin Thomson <> Thu, 09 July 2020 00:55 UTC

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Date: Wed, 08 Jul 2020 17:55:19 -0700
From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] Which DCID determines Initial keys (#3862)
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@martinthomson commented on this pull request.

> +The Destination Connection ID field from the first Initial packet sent by a
+client is used to determine packet protection keys for Initial packets.  These
+keys change after receiving a Retry packet; see Section 5.2 of {{QUIC-TLS}}.

However, this suggestion is incorrect.  You can change the value of the Destination Connection ID field.  After receiving an Initial, the client sets the Destination Connection ID field to the value the server chooses in the Source Connection ID field.  This updates the value used in Initial packets (such as an ACK), but does not change the keys.

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