Section: B.2.1.2.2 EAP TLS with subscription identifier privacy
Content: For EAP TLS, if the operator determines to provide subscription identifier privacy for the UE in TLS layer, the the EAP TLS server needs to support privacy either inherently (e.g., in TLS 1.3) or via separate privacy option (e.g., in TLS 1.2). If privacy is an option in TLS layer, then the operator needs to configure UE with the information that privacy-on-TLS layer is enabled. Further, following considerations need to be taken. In Step 1 of Figure B.2.1-1, it is important that calculation of SUCI, which is sent in NAS layer, is done using schemes other than "null-scheme". Otherwise, the subscription identifier protection provided by TLS layer becomes ineffective privacy-wise. Nevertheless, the "null-scheme" could be used in NAS layer while still preserving subscription identifier privacy, by omitting the username part from NAI as described in RFC 4282 clause 2.3 [y]. It would be analogous to using anonymous identifier in EAP, meaning that only realm part from NAI is included in SUCI which is sent in NAS layer. Thus formed SUCI can still be used to route the authentication request to AUSF. In Step 13 and 14 of Figure B.2.1-1, when TLS 1.2 is used, the UE would need to behave as described in "Section 2.1.4. Privacy" of RFC 5216 [38] where instead of sending the client certificate in cleartext over the air, the UE first sends TLS certificate (no cert) and only later sends TLS certificate after a TLS is setup.