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Re: [TLS] Design Alternatives for Kerberos + DH

Benjamin Kaduk <bkaduk@akamai.com> Fri, 16 October 2015 19:49 UTC

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To: Paul Wouters <paul@nohats.ca>, Rick van Rein <rick@openfortress.nl>
References: <56212653.6050702@openfortress.nl> <alpine.LFD.2.20.1510161445240.9839@bofh.nohats.ca>
From: Benjamin Kaduk <bkaduk@akamai.com>
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Date: Fri, 16 Oct 2015 14:48:58 -0500
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Cc: tls@ietf.org
Subject: Re: [TLS] Design Alternatives for Kerberos + DH
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On 10/16/2015 01:48 PM, Paul Wouters wrote:
> On Fri, 16 Oct 2015, Rick van Rein wrote:
>
>> 3) Similar to OpenPGP: Negotiate cert-type
>>
>> There is a cert-type for X.509 and for OpenPGP; add one for Kerberos
>> Tickets.
>>
>> PRO: Good integration with TLS: Tickets are transported in the
>> ClientCertificate, and an Authenticator is the ClientVerify.  DH is
>> independent and can move to the earlier phase for TLS 1.3.
>
> How is this type of TLS connection prevented from being MITM'ed by
> someone replaying kerberos tickets (which it cannot read itself)

I think it is not, if the Kerberos and DH parts are completely
orthogonal [and the Kerberos exchange is not mixed into the master
secret other than via the session hash].  Having the authenticator
include the DH public value or mixing the Kerberos session key into the
master secret are two options that come to mind right away.

-Ben

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