Re: [Emu] Consensus call on EAP-TLS key derivation

Alan DeKok <aland@deployingradius.com> Mon, 10 May 2021 12:50 UTC

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From: Alan DeKok <aland@deployingradius.com>
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Date: Mon, 10 May 2021 08:50:35 -0400
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Subject: Re: [Emu] Consensus call on EAP-TLS key derivation
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On May 9, 2021, at 1:54 PM, Joseph Salowey <joe@salowey.net> wrote:
> 
> We had discussion on the list on whether to include context in the key derivation, but we never closed on the issue of separating out the MSK and EMSK derivation.  As a result several implementers have gone down the path of implementing what is in draft 13 and not separating out the derivation.  The main difference is that draft 15 separated out the EMSK and MSK derivation using two different labels while draft 13 used a single label to derive key material which is partitioned into two keys.   The reason for the change was to enable different access control for these two different quantities for different callers, however in practice it is EAP-TLS application which needs access to both keys that is the caller of the TLS library so this separation is not particularly useful.   Therefore the recommendation is to align with implementation and derive the MSK and EMSK by partitioning the key material from the key material produced by a single label of the exporter function. 
> 
> Please respond to the list if you support the change below or not to revert some of the text in the key derivation section.  If you object to the change please state why.  Please respond by May 20,2021.

  We should revert to the -13 key derivations.

  Alan DeKok.