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Re: [radext] New draft: RFC6614bis (RADIUS/TLS)

Alan DeKok <aland@deployingradius.com> Fri, 28 October 2022 16:25 UTC

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From: Alan DeKok <aland@deployingradius.com>
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Date: Fri, 28 Oct 2022 12:25:48 -0400
Cc: Jan-Frederik Rieckers <rieckers@dfn.de>, Peter Deacon <peterd@iea-software.com>, radext@ietf.org
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To: Bernard Aboba <bernard.aboba@gmail.com>
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Subject: Re: [radext] New draft: RFC6614bis (RADIUS/TLS)
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On Oct 28, 2022, at 12:21 PM, Bernard Aboba <bernard.aboba@gmail.com> wrote:
> 
> Alan said: 
> 
> "Due to TLS version issues, a TLS-PSK MUST NOT be used across different versions of TLS."
> 
> [BA] What are the implications of this?  Does an operator need to configure distinct TLS-PSKs for TLS 1.2 and TLS 1.3??

  Arguably yes.

https://www.rfc-editor.org/rfc/rfc8446#appendix-E.7

...
   The constructions in TLS 1.2 and TLS 1.3 are different, although they
   are both based on HMAC.  While there is no known way in which the
   same PSK might produce related output in both versions, only limited
   analysis has been done.  Implementations can ensure safety from
   cross-protocol related output by not reusing PSKs between TLS 1.3 and
   TLS 1.2.


  My $0.02 is that TLS 1.3 is widely available, and RADIUS/TLS does not widely use TLS-PSK that I'm aware of.

  We should probably just mandate TLS 1.3 when TLS-PSK is being used with RADIUS/TLS.

  Alan DeKok.

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