Extensible Authentication Protocol Method for GSM Subscriber Identity Module, or EAP-SIM,
is an Extensible Authentication Protocol

Extensible Authentication Protocol

Extensible Authentication Protocol, or EAP, is an authentication framework frequently used in wireless networks and Point-to-Point connections. It is defined in RFC 3748, which made RFC 2284 obsolete, and was updated by RFC 5247....

 (EAP) mechanism for authentication and
session key distribution using the Subscriber Identity Module

Subscriber Identity Module

A subscriber identity module or subscriber identification module is an integrated circuit that securely stores the International Mobile Subscriber Identity and the related key used to identify and authenticate subscriber on mobile telephony devices .A SIM is held on a removable SIM card, which...

 (SIM) from the Global System for Mobile Communications (GSM). EAP-SIM is described in RFC 4186.

GSM cellular networks use a subscriber identity module (SIM) card to carry out user authentication. EAP-SIM use a SIM authentication algorithm between the client and an Authentication, Authorization and Accounting (AAA) server providing mutual authentication between the client and the network.

In EAP-SIM the communication between the SIM card and the Authentication Centre (AuC) replaces the need for a pre-established password between the client and the AAA server.