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

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 30 October 2020 12:39 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Achim Kraus <achimkraus@gmx.net>, Eric Rescorla <ekr@rtfm.com>, "Benjamin Kaduk" <kaduk@mit.edu>
CC: "tls@ietf.org" <tls@ietf.org>, "draft-ietf-tls-dtls-connection-id@ietf.org" <draft-ietf-tls-dtls-connection-id@ietf.org>
Thread-Topic: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07
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Date: Fri, 30 Oct 2020 12:39:03 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/-quGduxsZD-2bx9gaLgOrsb8NvM>
Subject: Re: [TLS] Fwd: Re: AD review of draft-ietf-tls-dtls-connection-id-07
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Achim Kraus <achimkraus@gmx.net> writes:

>2. Why should a "uint16 iv_length" be added?

To make it explicit which of the bits being hashed is the IV.  This is one of
the flaws of things like OAEP, there are a large number of implicitly-sized
fields controlled by external, unauthenticated parameters, so you can make the
verifier see fields as other, nearby fields (I'm using OAEP as an example
because it's particularly bad, there are so many optional values controlled by
external unauthenticated data that you can have all sorts of fun with it).

>2.b If it should be added, why in the middle? It's not on the wire and so I
>would assume, if at all, to have that at the begin.

It precedes the IV, i.e. the field that it describes.

Peter.