Subject: Re: [TLS] Question about TLS_RSA_WITH_3DES_EDE_CBC_SHA

From: Stefan Winter <[email-masked]>
Date: Mon, 04 Jul 2011 14:29:11 +0200

Hello,

there I was, naively hoping for a simple "Yes or No" answer :-)

My hopefully acceptable takeaway of this thread is that
TLS_RSA_WITH_3DES_EDE_CBC_SHA *supports* three-key operation, which
would be acceptable as per NIST.

I understand there is also a *risk* that if the dice fall very badly,
the actual encryption strength in that specific TLS session may exhibit
weaker cryptographic strength.

Thanks to all who responded!

Greetings,

Stefan Winter

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Stefan WINTER
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Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et de la Recherche
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From: Martin Rex <[email-masked]>
Date: Mon, 4 Jul 2011 15:12:38 +0200 (MEST)

> Thanks to all who responded!

I'm sorry for causing the confusion.

In _my_ interpretation of the NIST guidance, TLS_RSA_WITH_3DES_EDE_CBC_SHA
is a 3-key triple des.  While they recommend weak key avoidance for
DES, they do not require it.  the sub-key collisions for 3-DES could
be viewed as additional weak keys for 3DES compared to single-DES.

Dealing with weak keys and non-dense key spaces is common for
traditional key generation (assymetric and symmetric DES), but seems
fairly uncommon for algorithmic key derivation of symmetric and MAC
traffic keys.

-Martin