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 is an authentication framework providing for the transport and usage of keying material and parameters generated by EAP methods. There are many methods defined by RFCs and a number of vendor specific methods and new proposals exist. EAP is not a wire protocol; instead it only defines message formats. Each protocol that uses EAP defines a way to encapsulate EAP messages within that protocol's messages.
EAP is an authentication framework, not a specific authentication mechanism. It provides some common functions and negotiation of authentication methods called EAP methods. There are currently about 40 different methods defined. Methods defined in IETF RFCs include EAP-MD5, EAP-POTP, EAP-GTC, EAP-TLS, EAP-IKEv2, EAP-SIM, EAP-AKA. Additionally a number of vendor-specific methods and new proposals exist. Commonly used modern methods capable of operating in wireless networks include EAP-TLS, EAP-SIM, EAP-AKA, LEAP and EAP-TTLS. Requirements for EAP methods used in wireless LAN authentication are described in RFC 4017.
The standard also describes the conditions under which the AAA key management requirements described in RFC 4962 can be satisfied.
The Lightweight Extensible Authentication Protocol (LEAP) is a proprietary EAP method developed by Cisco Systems prior to the IEEE ratification of the 802.11i security standard. Cisco distributed the protocol through the CCX (Cisco Certified Extensions) as part of getting 802.1X and dynamic WEP adoption into the industry in the absence of a standard. There is no native support for LEAP in any Windows operating system, but it is widely supported by third party client software most commonly included with WLAN (wireless LAN) devices. LEAP support for Microsoft Windows 7 and Microsoft Windows Vista can be added by downloading a client add in from Cisco that provides support for both LEAP and EAP-FAST. Due to the wide adoption of LEAP in the networking industry many other WLAN vendors claim support for LEAP.
LEAP uses a modified version of MS-CHAP, an authentication protocol in which user credentials are not strongly protected and easily compromised; an exploit tool called ASLEAP was released in early 2004 by Joshua Wright. Cisco recommends that customers who absolutely must use LEAP do so only with sufficiently complex passwords, though complex passwords are difficult to administer and enforce. Cisco's current recommendation is to use newer and stronger EAP protocols such as EAP-FAST, PEAP, or EAP-TLS.
EAP-Transport Layer Security (EAP-TLS), defined in RFC 5216, is an IETF open standard that uses the Transport Layer Security (TLS) protocol, and is well-supported among wireless vendors. The security of TLS is strong provided the user understands potential warnings about false credentials. It uses PKI to secure communication to a RADIUS authentication server or another type of authentication server.
EAP-TLS is the original, standard wireless LAN EAP authentication protocol. Though it is rarely deployed, EAP-TLS is still considered one of the most secure EAP standards available and is universally supported by all manufacturers of wireless LAN hardware and software. The requirement for a client-side certificate, however unpopular it may be, is what gives EAP-TLS its authentication strength and illustrates the classic convenience vs. security trade-off. A compromised password is not enough to break into EAP-TLS enabled systems because the intruder still needs to have the client-side private key. The highest security available is when client-side keys are housed in smart cards. This is because there is no way to steal a certificate's corresponding private key from a smart card without stealing the card itself. It is more likely that the physical theft of a smart card would be noticed (and the smart card immediately revoked) than a (typical) password theft would be noticed. Until April 2005, EAP-TLS was the only EAP type vendors needed to certify for a WPA or WPA2 logo. There are client and server implementations of EAP-TLS in 3Com, Apple, Avaya, Brocade Communications, Cisco, Enterasys Networks, Foundry, Hirschmann, HP, Juniper, and Microsoft, and open source operating systems. EAP-TLS is natively supported in Mac OS X 10.3 and above, wpa_supplicant, Windows 2000 SP4, Windows XP and above, Windows Mobile 2003 and above, Windows CE 4.2, and Apple's iOS mobile operating system.
Unlike most TLS implementations of HTTPS, such as major web browsers, the majority TLS implementations of EAP-TLS require the client to use X.509 certificates, which some have identified as having the potential to dramatically reduce adoption of EAP-TLS. As of 22 August 2012, hostapd (and wpa_supplicant) added support in its Git repository for an UNAUTH-TLS vendor specific EAP type which only does server authentication. This will allow for situations much like HTTPS, where a wireless hotspot allows free access and does not authenticate station clients but station clients wish to use encryption (IEEE 802.11i-2004 i.e. WPA2) and potentially authenticate the wireless hotspot.
EAP-MD5 was the only IETF Standards Track based EAP method when it was first defined in the original RFC for EAP, RFC 2284. It offers minimal security; the MD5 hash function is vulnerable to dictionary attacks, and does not support key generation, which makes it unsuitable for use with dynamic WEP, or WPA/WPA2 enterprise. EAP-MD5 differs from other EAP methods in that it only provides authentication of the EAP peer to the EAP server but not mutual authentication. By not providing EAP server authentication, this EAP method is vulnerable to man-in-the-middle attacks. EAP-MD5 support was first included in Windows 2000 and deprecated in Windows Vista.
EAP-POTP (Protected One-Time Password), which is described in RFC 4793, is an EAP method developed by RSA Laboratories that uses one-time password (OTP) tokens, such as a handheld hardware device or a hardware or software module running on a personal computer, to generate authentication keys. EAP-POTP can be used to provide unilateral or mutual authentication and key material in protocols that use EAP.
The EAP-POTP method provides two-factor user authentication, meaning that a user needs both physical access to a token and knowledge of a personal identification number (PIN) to perform authentication.
EAP-PSK, defined in RFC 4764, is an EAP method for mutual authentication and session key derivation using a Pre-Shared Key (PSK). It provides a protected communication channel, when mutual authentication is successful, for both parties to communicate and is designed for authentication over insecure networks such as IEEE 802.11.
EAP-PSK is documented in an experimental RFC that provides a lightweight and extensible EAP method that does not require any public-key cryptography. The EAP method protocol exchange is done in a minimum of four messages.
EAP-pwd, defined in RFC 5931, is an EAP method which uses a shared password for authentication. The password may be a low-entropy one and may be drawn from some set of possible passwords, like a dictionary, which is available to an attacker. The underlying key exchange is resistant to active attack, passive attack, and dictionary attack.
EAP-Tunneled Transport Layer Security (EAP-TTLS) is an EAP protocol that extends TLS. It was co-developed by Funk Software and Certicom and is widely supported across platforms. Microsoft did not incorporate native support for the EAP-TTLS protocol in Windows XP, Vista, or 7. Supporting TTLS on these platforms requires third-party ECP (Encryption Control Protocol) certified software. Microsoft Windows started EAP-TTLS support with Windows 8, however Windows Phone 8 does NOT support EAP-TTLS.
After the server is securely authenticated to the client via its CA certificate and optionally the client to the server, the server can then use the established secure connection ("tunnel") to authenticate the client. It can use an existing and widely deployed authentication protocol and infrastructure, incorporating legacy password mechanisms and authentication databases, while the secure tunnel provides protection from eavesdropping and man-in-the-middle attack. Note that the user's name is never transmitted in unencrypted clear text, improving privacy.
EAP-IKEv2 is an EAP method based on the Internet Key Exchange protocol version 2 (IKEv2). It provides mutual authentication and session key establishment between an EAP peer and an EAP server. It supports authentication techniques that are based on the following types of credentials:
- Asymmetric key pairs - public/private key pairs where the public key is embedded into a digital certificate, and the corresponding private key is known only to a single party.
- Passwords - low-entropy bit strings that are known to both the server and the peer.
- Symmetric keys - high-entropy bit strings that are known to both the server and the peer.
It is possible to use a different authentication credential (and thereby technique) in each direction. For example, the EAP server authenticates itself using public/private key pair and the EAP peer using symmetric key. In particular, the following combinations are expected to be used in practice:
|EAP server||EAP peer|
|Asymmetric key pair||Asymmetric key pair|
|Asymmetric key pair||Symmetric key|
|Asymmetric key pair||Password|
|Symmetric key||Symmetric key|
EAP-FAST (Flexible Authentication via Secure Tunneling) is a protocol proposal by Cisco Systems as a replacement for LEAP. The protocol was designed to address the weaknesses of LEAP while preserving the "lightweight" implementation. Use of server certificates is optional in EAP-FAST. EAP-FAST uses a Protected Access Credential (PAC) to establish a TLS tunnel in which client credentials are verified.
EAP-FAST has three phases:
|Phase 0||In-band provisioning—provide the peer with a shared secret to be used in secure phase 1 conversation||Uses Authenticated Diffie-Hellman Protocol (ADHP). This phase is independent of other phases; hence, any other scheme (in-band or out-of-band) can be used in the future.||Eliminate the requirement in the client to establish a master secret every time a client requires network access|
|Phase 1||Tunnel establishment||Authenticates using the PAC and establishes a tunnel key||Key establishment to provide confidentiality and integrity during the authentication process in phase 2|
|Phase 2||Authentication||Authenticates the peer||Multiple tunneled, secure authentication mechanisms (credentials exchanged)|
When automatic PAC provisioning is enabled, EAP-FAST has a slight vulnerability where an attacker can intercept the PAC and use that to compromise user credentials. This vulnerability is mitigated by manual PAC provisioning or by using server certificates for the PAC provisioning phase.
It is worth noting that the PAC file is issued on a per-user basis. This is a requirement in RFC 4851 sec 7.4.4 so if a new user logs on the network from a device, a new PAC file must be provisioned first. This is one reason why it is difficult not to run EAP-FAST in insecure anonymous provisioning mode. The alternative is to use device passwords instead, but then the device is validated on the network not the user.
EAP-FAST can be used without PAC files, falling back to normal TLS.
EAP-FAST is natively supported in Apple OS X 10.4.8 and newer. Cisco supplies an EAP-FAST module for Windows Vista  and later operating systems which have an extensible EAPHost architecture for new authentication methods and supplicants.
EAP-FAST is defined in RFC 4851.
EAP for GSM Subscriber Identity Module (EAP-SIM) is used for authentication and session key distribution using the Subscriber Identity Module (SIM) from the Global System for Mobile Communications (GSM).
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.
The A3/A8 algorithms are being run a few times, with different 128 bit challenges, so there will be more 64 bit Kc-s which will be combined/mixed to create stronger keys (Kc-s won't be used directly). The lack of mutual authentication in GSM has also been overcome.
EAP-SIM is described in RFC 4186.
Extensible Authentication Protocol Method for Universal Mobile Telecommunications System (UMTS) Authentication and Key Agreement (EAP-AKA), is an EAP mechanism for authentication and session key distribution using the UMTS Subscriber Identity Module (USIM). EAP-AKA is defined in RFC 4187.
EAP Generic Token Card, or EAP-GTC, is an EAP method created by Cisco as an alternative to PEAPv0/EAP-MSCHAPv2 and defined in RFC 2284 and RFC 3748. EAP-GTC carries a text challenge from the authentication server, and a reply generated by a security token. The PEAP-GTC authentication mechanism allows generic authentication to a number of databases such as Novell Directory Service (NDS) and Lightweight Directory Access Protocol (LDAP), as well as the use of a one-time password.
EAP with the Encrypted key exchange, or EAP-EKE, is one of the few EAP methods that provide secure mutual authentication using short passwords and no need for public key certificates. It is a 3-round exchange, based on the Diffie-Hellman variant of the well-known EKE protocol.
EAP-EKE is specified in RFC 6124.
EAP is not a wire protocol; instead it only defines message formats. Each protocol that uses EAP defines a way to encapsulate EAP messages within that protocol's messages.
IEEE 802.1X 
The encapsulation of EAP over IEEE 802 is defined in IEEE 802.1X and known as "EAP over LANs" or EAPOL. EAPOL was originally designed for IEEE 802.3 ethernet in 802.1X-2001, but was clarified to suit other IEEE 802 LAN technologies such as IEEE 802.11 wireless and Fiber Distributed Data Interface (ISO 9314-2) in 802.1X-2004. The EAPOL protocol was also modified for use with IEEE 802.1AE (MACsec) and IEEE 802.1AR (Initial Device Identity, IDevID) in 802.1X-2010.
When EAP is invoked by an 802.1X enabled Network Access Server (NAS) device such as an IEEE 802.11i-2004 Wireless Access Point (WAP), modern EAP methods can provide a secure authentication mechanism and negotiate a secure private key (Pair-wise Master Key, PMK) between the client and NAS which can then be used for a wireless encryption session utilizing TKIP or CCMP (based on AES) encryption.
The Protected Extensible Authentication Protocol, also known as Protected EAP or simply PEAP, is a protocol that encapsulates EAP within a potentially encrypted and authenticated Transport Layer Security (TLS) tunnel. The purpose was to correct deficiencies in EAP; EAP assumed a protected communication channel, such as that provided by physical security, so facilities for protection of the EAP conversation were not provided.
PEAP was jointly developed by Cisco Systems, Microsoft, and RSA Security. PEAPv0 was the version included with Microsoft Windows XP and was nominally defined in draft-kamath-pppext-peapv0-00. PEAPv1 and PEAPv2 were defined in different versions of draft-josefsson-pppext-eap-tls-eap. PEAPv1 was defined in draft-josefsson-pppext-eap-tls-eap-00 through draft-josefsson-pppext-eap-tls-eap-05, and PEAPv2 was defined in versions beginning with draft-josefsson-pppext-eap-tls-eap-06.
RADIUS and Diameter 
Both the RADIUS and Diameter AAA protocols can encapsulate EAP messages. They are often used by Network Access Server (NAS) devices to forward EAP packets between IEEE 802.1X endpoints and AAA servers to facilitate IEEE 802.1X.
The Protocol for Carrying Authentication for Network Access (PANA) is an IP-based protocol that allows a device to authenticate itself with a network to be granted access. PANA will not define any new authentication protocol, key distribution, key agreement or key derivation protocols; for these purposes, EAP will be used, and PANA will carry the EAP payload. PANA allows dynamic service provider selection, supports various authentication methods, is suitable for roaming users, and is independent from the link layer mechanisms.
EAP was originally an authentication extension for the Point-to-Point Protocol (PPP). PPP has supported EAP since EAP was created as an alternative to the Challenge-Handshake Authentication Protocol (CHAP) and the Password Authentication Protocol (PAP), which were eventually incorporated into EAP.
See also 
- "AAA and Network Security for Mobile Access. RADIUS, DIAMETER, EAP, PKI and IP mobility". M Nakhjiri. John Wiley and Sons, Ltd.
- RFC 3748, § 1
- George Ou (January 11, 2007). "Ultimate wireless security guide: An introduction to LEAP authentication". TechRepublic. Retrieved 2008-02-17.
- Dan Jones (October 1, 2003). "Look Before You LEAP". Unstrung. Retrieved 2008-02-17.
- Rand Morimoto; Kenton Gardinier, Michael Noel and Joe Coca (2003). Microsoft Exchange Server 2003 Unleashed. Sams. p. 244. ISBN 978-0-672-32581-6.
- "Understanding the updated WPA and WPA2 standards". techrepublic.com. Retrieved 2008-02-17.
- Byrd, Christopher (5 May 2010). "Open Secure Wireless".
- "Add UNAUTH-TLS vendor specific EAP type". hostapd. Retrieved 2012-10-19.
- "Alternative Encryption Schemes: Targeting the weaknesses in static WEP". Ars Technica. Retrieved 2008-02-17.
- "922574", Knowledge Base, Microsoft
- FreeRADIUS EAP module rlm_eap_pwd
- Added support for EAP-PWD per RFC 5931
-  Secure-authentication with only a password
- EAP-TTLS on Windows 8 (Build 8250)
- TTLSv1 Internet draft
- "Ultimate wireless security guide: A primer on Cisco EAP-FAST authentication". techrepublic.com. Retrieved 2008-02-17.
- How do I install CISCO EAP-FAST on my computer?
- EAPHost in Windows
- RFC 3748, § 3.3
- RFC 3748, § 7.12
- IEEE 802.1X-2001, § 7
- IEEE 802.1X-2004, § 3.2.2
- IEEE 802.1X-2010, § 5
- Microsoft's PEAP version 0, draft-kamath-pppext-peapv0-00, §1.1
- Protected EAP Protocol (PEAP) Version 2, draft-josefsson-pppext-eap-tls-eap-10, abstract
- Protected EAP Protocol (PEAP) Version 2, draft-josefsson-pppext-eap-tls-eap-10, §1
- Protected EAP Protocol (PEAP) Version 2, draft-josefsson-pppext-eap-tls-eap-07, §1
- Protected EAP Protocol (PEAP), draft-josefsson-pppext-eap-tls-eap-05, §2.3
- Protected EAP Protocol (PEAP), draft-josefsson-pppext-eap-tls-eap-06, §2.3
- Protected EAP Protocol (PEAP) Version 2, draft-josefsson-pppext-eap-tls-eap-10, §2
- RFC 3748: Extensible Authentication Protocol (EAP) (June 2004)
- RFC 5247: Extensible Authentication Protocol (EAP) Key Management Framework (August 2008)
- Configure RADIUS for secure 802.1x wireless LAN
- How to self-sign a RADIUS server for secure PEAP or EAP-TTLS authentication
- Wifiradis a free online RADIUS server for secure PEAP mschap-v2 authentication
- Extensible Authentication Protocol on Microsoft TechNet
- EAPHost in Windows Vista and Windows Server 2008
- "IETF EAP Method Update (emu) Working Group"