# Understanding Server Authentication in WPA3 Enterprise
## 3 Server Authentication in WPA3 Enterprise  
In this section, we provide a simplified description of the mechanisms provided by WPA3 Enterprise for reducing the risks associated with AS authentication. Our description does not cover all possible execution patterns and focuses instead on those that are most useful for understanding the defensive power of WPA3 Enterprise. We refer to the original document for full details [1]. First and foremost, WPA3 Enterprise forbids such supplicant configuration options as \"skip certificate validation\" or \"accept any certificate\". WPA3 Enterprise dictates that if the supplicant fails to verify the server identity during Phase 1, the supplicant _cannot_ enter Phase 2 automatically; the supplicant may enter Phase 2 only if the user _explicitly_ accepts trust in the certificate provided by the AS--for example, by means of a dialog window. This interactive mechanism is called User Override of Server Certificate (UOSC). The server identity in Phase 1 is considered verified if the AS has the name specified in the network profile or it has the same name as in the last successful connection. The two more common scenarios in which server identity validation fails and thus UOSC comes into play are:  
* The supplicant is _not_ configured with a network profile. * The supplicant executes Phase 1 with an AS whose name is _different_ from the name of the AS upon the last successful connection. The fact that UOSC requires the _explicit_ involvement of the user is a significant security improvement over WPA2 Enterprise; attack opportunities are limited only to when the user is actively interacting with the supplicant in order to connect to the enterprise network--e.g., the smartphone cannot enter Phase 2 with an ET automatically while the user is walking with a smartphone in his/her pocket. Second, WPA3 Enterprise allows network administrators to constrain how applicants may learn the name of the AS--i.e., how applicants may obtain the certificate containing that name. 1. A supplement may obtain the certificate from the AS itself, upon _every_ connection. 2. A supplement may obtain the certificate from the AS itself only upon the _first_ connection; subsequent connections must use the same certificate of the first connection. 3. A supplement can _never_ obtain the certificate from the AS itself. The supplement must be configured with a network profile--that is, it can only obtain the certificate by means of some out-of-band (secure) communication channel. Option 1 is essentially equivalent to WPA2 Enterprise but with a crucial difference: when the supplement observes that the name of the AS has changed, the requirement for explicit user involvement results in a much more secure setting, as observed above. Option 2 is a form of Trust on First Use (TOFU). If the first connection is performed with the legitimate AS, then the supplement will never enter Phase 2 with an ET. The user could explicitly accept trust in a certificate sent by an ET and enter Phase 2 (thereby leaking credential material to the attacker), but only if the supplement has never connected to the enterprise network before. Server authentication based on forms of TOFU is widely used for secure remote access to network services with the Secure Shell (SSH) protocol [23] and was also proposed for enterprise Wi-Fi networks in a framework based on self-signed public keys without any need for certification authorities [19]. Option 3 is the most secure one: the supplement will connect only to the AS that authenticates itself with a certificate identical to the one in the network profile already installed. With this option, an attacker may follow two tactics:  
* Attack the communication channel that applicants use for obtaining the network profile. The security properties of this channel will depend on the security policy of the organization and are orthogonal to WPA3 Enterprise. * Attack applicants that have never connected to the network and have not (yet) installed the network profile.