Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07

Achim Kraus <achimkraus@gmx.net> Sun, 11 October 2020 18:12 UTC

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To: Ilari Liusvaara <ilariliusvaara@welho.com>
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From: Achim Kraus <achimkraus@gmx.net>
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Date: Sun, 11 Oct 2020 20:12:30 +0200
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/GTaQpu0jF9EgeVe290fdqZUE538>
Subject: Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07
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Hi Ilari,

> The problem is the follows:
>
> Take the following input to the MAC (MtE case):
>
> <seqnum> 19 FE FD 63 01 00 05 04 00 02 FF 17
>
> There is no way to tell from that input if it is:
>
> - Application record on CID 63 containing 04 00 02 FF, or
> - Application record on CID 63 01 00 05 containing FF.
>

Maybe you check your example?

Does the 1. assume cid-length := 1?
And the 2. cid-length := 4?


The dtls-record will then contain:

(remove cid-length 01, cid-length is NOT encoded in the dtls-record!)

19 FE FD <seqnum> 63 00 05 04 00 02 FF 17

or

(remove cid-length 04)

19 FE FD <seqnum> 63 01 00 05 00 02 FF 17

For me this seems to be different input to the MAC, if the cid-length is
left out. My feeling is, your example proves my opinion, that it's
better to remove the cid-length from the MAC.

best regards
Achim Kraus