Hi Oleg, "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 CA bundle, then effectively any server can obtain a certificate which will be trusted for EAP authentication by the Peer."
Do you have any concrete suggestions for improvements of this section Oleg? This second part of the paragraph seems to discuss what happens if the advice in the first half is not followed. When I conect to Ericsson's internal WiFi network, I would expect checks that I am taking to the EAP server, not the printer. I would also expect checks that I talk with Ericsson EAP server, and not Huawei's or Nokia's EAP server. Should Network be replaced by a better term? Some comments from me on Section 2.2 "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." This requires some security consideration, I think.... "Iimplementations MAY rely on system-wide root CA certificate bundles for authenticating the server certificate. If server name matching is not used" This seems to indicate that it is ok to not do any server authentication. The TLS CertificateVerify message does not give any authentication in itself, it only enables the application using TLS to do authentication. Section 2.2. "Identity Verification" needs to match current deployments and uses of EAP-TLS. But if EAP-TLS does not even mandate server authentication, does it really make sense to mandate revocation? Cheers, John From: Emu <[email protected]> on behalf of Oleg Pekar <[email protected]> Date: Monday, 31 May 2021 at 17:46 To: Joseph Salowey <[email protected]> Cc: [email protected] <[email protected]>, EMU WG <[email protected]> Subject: Re: [Emu] EAP-TLS 1.3 Section 2.2 text This version is fine. Just the term "EAP servers for the network" still looks confusing to me. Maybe we can use instead the more detailed explanation that you provided above. On Tue, May 25, 2021 at 7:45 AM Joseph Salowey <[email protected]<mailto:[email protected]>> wrote: I made some changes to the pull request to address some of the comments and make the text clearer: The EAP peer identity provided in the EAP-Response/Identity is not authenticated by EAP-TLS. Unauthenticated information MUST 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) in the SubjectAltName (SAN) extension. Since EAP-TLS deployments may use more than one EAP server, each with a different certificate, EAP peer implementations SHOULD allow for the configuration of a unique trusted root (CA certificate) to authenticate the server certificate and one or more server names to match against the SubjectAltName (SAN) extension in the server certificate. To simplify name matching, an EAP-TLS deployment can assign a name to represent an authorized EAP server and EAP Server certificates can include this name in the list of SANs for each certificate that represents an EAP-TLS server. 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 Thu, May 20, 2021 at 10:23 PM Joseph Salowey <[email protected]<mailto:[email protected]>> wrote: On Wed, May 19, 2021 at 5:58 AM Alan DeKok <[email protected]<mailto:[email protected]>> wrote: On May 19, 2021, at 8:37 AM, Oleg Pekar <[email protected]<mailto:[email protected]>> wrote: > After thinking a bit more about it - for the sake of the client > implementation clarity, would it be better if we provide the strict algorithm > for server identity check or maybe reference RFC 6125. Given the time frame and what we know, I think the existing text is OK. [Joe] In addition the intent of the text is to make implementers aware of the issues and provide some guidance as to how to solve the problem. I don't think we can dictate too much more at this point. We can have follow-on work to have a strict algorithm is depolyers and implementers feel it is necessary. This is what wpa_supplicant does in it's implementation, and it seems to work fine. Apple appears to do the same thing: https://opensource.apple.com/source/eap8021x/eap8021x-264.30.3/EAP8021X.fproj/EAPTLSUtil.c.auto.html Look for "trusted_server_names", which leads to: https://opensource.apple.com/source/eap8021x/eap8021x-156/EAP8021X.fproj/EAPTLSUtil.c server_name_matches_server_names() Which checks if the name from the cert is an exact match for one of the "trusted_server_names", or contains "*." followed by a suffix which is one of the trusted server names. I think it's past the time where this document can ask supplicants to change their behavior. We know what the supplicants do, it's not wrong, and it seems to work. So let's document that, and move on. Alan DeKok.
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