Re: [Emu] EAP-TLS 1.3 Section 2.2 text

Russ Housley <housley@vigilsec.com> Mon, 17 May 2021 16:06 UTC

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From: Russ Housley <housley@vigilsec.com>
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Date: Mon, 17 May 2021 12:06:07 -0400
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Cc: Alan DeKok <aland@deployingradius.com>, EMU WG <emu@ietf.org>
To: Joe Salowey <joe@salowey.net>
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Subject: Re: [Emu] EAP-TLS 1.3 Section 2.2 text
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Nit: RFC 5280 (see Section 4.2.1.6) talks about the subject alternative name extension, which as an ASN.1 definition for SubjectAltName.  So, please do not refer to subjectAlternativeName.

Russ


> On May 15, 2021, at 8:21 PM, Joseph Salowey <joe@salowey.net> wrote:
> 
> I proposed a PR#72 <https://github.com/emu-wg/draft-ietf-emu-eap-tls13/pull/72> based on this suggestion. The resulting text for the section is below.  Please review to see if it is OK.
> 
> Thanks,
> 
> Joe
> 
> 2.2.  Identity Verification
> 
>    This section updates Section 2.2 of [RFC5216].
> 
>    The EAP peer identity provided in the EAP-Response/Identity is not
>    authenticated by EAP-TLS.  Unauthenticated information SHALL NOT be
>    used for accounting purposes or to give authorization.  The
>    authenticator and the EAP-TLS server MAY examine the identity
>    presented in EAP-Response/Identity for purposes such as routing and
>    EAP method selection.  EAP-TLS servers MAY reject conversations if
>    the identity does not match their policy.  Note that this also
>    applies to resumption, see Sections 2.1.3, 5.6, and 5.7.
> 
>    The EAP server identity in the TLS server certificate is typically a
>    fully qualified domain name (FQDN).  EAP peer implementations SHOULD
>    allow users to configure a unique trust root (CA certificate) and a
>    server name to authenticate the server certificate and match the
>    subjectAlternativeName (SAN) extension in the server certificate with
>    the configured server name.  EAP-TLS deployments will often use more
>    than one EAP server.  In this case each EAP server may have a
>    different certificate.  To facilitate SAN matching, EAP Server
>    certificates can include the same name in the list of SANs for each
>    certificate that represents the EAP-TLS servers.  EAP-TLS peers
>    SHOULD allow for the configuration of multiple EAP server names since
>    deployments may choose to use multiple EAP servers each with their
>    own certificate.  If server name matching is not used, then peers may
>    end up trusting servers for EAP authentication that are not intended
>    to be EAP servers for the network.  If name matching is not used with
>    a public root CA, then effectively any server can obtain a
>    certificate which will be trusted for EAP authentication by the Peer.
>    
>    The process of configuring a root CA certificate and a server name is
>    non-trivial and therefore automated methods of provisioning are
>    RECOMMENDED.  For example, the eduroam federation [RFC7593] provides
>    a Configuration Assistant Tool (CAT) to automate the configuration
>    process.  In the absence of a trusted root CA certificate (user
>    configured or system-wide), EAP peers MAY implement a trust on first
>    use (TOFU) mechanism where the peer trusts and stores the server
>    certificate during the first connection attempt.  The EAP peer
>    ensures that the server presents the same stored certificate on
>    subsequent interactions.  Use of a TOFU mechanism does not allow for
>    the server certificate to change without out-of-band validation of
>    the certificate and is therefore not suitable for many deployments
>    including ones where multiple EAP servers are deployed for high
>    availability.
> 
> On Mon, May 10, 2021 at 5:11 AM Alan DeKok <aland@deployingradius.com <mailto:aland@deployingradius.com>> wrote:
> On May 9, 2021, at 9:16 PM, Joseph Salowey <joe@salowey.net <mailto:joe@salowey.net>> wrote:
> > [Joe]  This is a good question.  There are multiple ways this could be addressed.  All servers should have one of their list of SANs that matches the name used for EAP servers.  Another option is for supplicants to allow for the configuration of multiple certificates or allow for a wild card match.
> 
>   FWIW, wpa_supplicant has a list of allowed host names for SAN.  I don't think it allows wildcards.
> 
> >   How about this text addition:
> > 
> > "EAP-TLS deployments will often use more than one EAP server.  In this case each EAP server may have a different certificate.  To facilitate the SAN matching, EAP Server certificates can include the same name in the list of SANs for each certificate that represents the EAP-TLS servers.  EAP-TLS peers SHOULD allow for the configuration of multiple EAP server names since deployments may choose to use multiple EAP servers each with their own certificate." 
> 
>   That's good.
> 
> > [Joe] Is your comment about HA and the TOFU mechanism?  I'm not really sure how the TOFU mechanism is supposed to work and be secure.  Perhaps we should remove the TOFU mechanism text or state that it does not work well in all HA configurations (where different servers use different certificates)
> 
>   Perhaps just state that it does not work well in HA configurations.
> 
>   I don't think TOFU can be secure here.
> 
>   Alan DeKok.
> 
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