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 <[email protected]> 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 <[email protected] 
> <mailto:[email protected]>> wrote:
> On May 9, 2021, at 9:16 PM, Joseph Salowey <[email protected] 
> <mailto:[email protected]>> 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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