Using EAP-SIM for WLAN Authentication yliqiang@gmail.com 2005-9-13

Definition(定义) EAP-SIM is an Extensible Authentication Protocol (EAP) [RFC3748] mechanism for authentication and session key distribution using the Global System for Mobile communications (GSM) Subscriber Identity Module (SIM). 用GSM-SIM卡作为EAP的认证和密匙分发机制 EAP-SIM

EAP Introduction (简介) EAP is an authentication framework which supports multiple authentication methods. 支持多种认证机制的认证框架。 EAP typically runs directly over data link layers such as Point-to-Point Protocol (PPP) or IEEE 802 EAP 通常直接运行在数据链路层如 PPP或IEEE 802 EAP-SIM

EAP Introduction (简介) EAP permits the use of a backend authentication server,with the authenticator acting as a pass-through for some or all methods and peers. EAP 允许使用后台认证服务器，把认证端作为一些或全部认证机制的转发者。 Conceptually, EAP implementations consist of the following components: 从概念上讲，EAP的实现有下面这些组件构成。 EAP-SIM

IEEE 802.1X EAPOL Lower Layer Peer(被认证者) Authenticator (认证者) EAP-SIM

Pass-through Authenticator (认证者) IEEE 802.1X EAPOL Lower Layer Peer(被认证者) Pass-through Authenticator (认证者) Radius Protocol Authentication Server (认证服务器) AAA:Authentication(认证）, Authorization (授权), and Accounting (记帐) EAP-SIM

GSM authentication(认证) RAND is a 128-bit random challenge issued from the base station to the mobile. RAND 是基站发给移动台(手机)的128比特长随机数。 SRES is a 32-bit response generated by A3 issued from the mobile to the base station SRES 是移动台(手机)发给基站的32比特长响应,由A3生成。 EAP-SIM

GSM authentication(认证) Kc is a 64-bit Cipher Key, used for A5. Kc是64比特长密匙，由A8生成用于数据加密(A5)。 Ki is the SIM’s 128-bit individual subscriber key. Ki是128比特长SIM卡的密匙(拥有标识)。 A3/A8 are specified by each operator rather than being fully standardized,but usually implemented together as COMP128. A3/A8定义了算法的输入输出，具体实现由厂商决定，实际上厂商都采用了COMP128，它同时实现了A3,A8。 EAP-SIM

EAP-SIM Introduction(简介) Peer SIM Card Authenticator AAA/RADIUS GSM/MAP/SS7 Gateway SS7 Network GSM Authentication Center builds on underlying GSM mechanisms 构建在GSM认证机制之上。 EAP-SIM

EAP-SIM Introduction(简介) Provides mutual authentication 支持相互认证。 several RAND challenges are used for generating several 64-bit Kc keys, which are combined to constitute stronger keying material. 多次挑战生成多个Kc,组合起来生成更强的相关密匙。 EAP-SIM

EAP-SIM Introduction(简介) EAP-SIM specifies optional support for protecting the privacy of subscriber identity using the same concept as GSM, which is using pseudonyms/temporary identifiers. EAP-SIM支持用户身份保密(可选)。 It also specifies an optional fast re-authentication procedure. 支持快速重复认证(可选) EAP-SIM

EAP-SIM Full Authentication Procedure(完全认证过程) Peer Authenticator | EAP-Request/Identity | |<---------------------------------------------------------| | | | EAP-Response/Identity | |--------------------------------------------------------->| | EAP-Request/SIM/Start (AT_VERSION_LIST) | | EAP-Response/SIM/Start (AT_NONCE_MT, AT_SELECTED_VERSION)| | EAP-Request/SIM/Challenge (AT_RAND, AT_MAC) | +-------------------------------------+ | | Peer runs GSM algorithms, verifies | | | AT_MAC and derives session keys | | | EAP-Response/SIM/Challenge (AT_MAC) | | EAP-Success | EAP-SIM Full Authentication Procedure(完全认证过程) EAP-SIM

Key Generation MK = SHA1(Identity|n*Kc| NONCE_MT| Version List| Selected Version) K_aut , K_encr , MSK and EMSK are derived from MK using Pseudo-Random number Function (PRF) Request AT_MAC = HMAC-SHA1-128(K_aut, EAP packet| NONCE_MT) Response AT_MAC = HMAC-SHA1-128(K_aut,EAP packet| n*SRES) In the formula above, the "|" character denotes concatenation. Nonce A value that is used at most once or that is never repeated within the same cryptographic context. MAC Message Authentication Code EAP-SIM

Indication of vulnerabilities(弱点) The security of the A3 and A8 algorithms is important to the security of EAP-SIM. Some A3/A8 algorithms have been compromised; see for example [GSM Cloning] for discussion about the security of COMP-128 version 1. Note that several revised versions of the COMP-128 A3/A8 algorithm have been devised after the publication of these weaknesses and that the publicly specified GSM-MILENAGE [3GPP TS 55.205] algorithm is not vulnerable to any known attacks. A3/A8算法的安全性对EAP-SIM是至关重要的。COMP128-v1已经被破解(当前市面上大部分SIM卡用的是COMP128-v1),修订过的COMP128 v2,v3以及公开标准的GSM-MILENAGE,当前还没有方法攻破。 EAP-SIM

Indication of vulnerabilities(弱点) Mutual Authentication and Triplet Exposure EAP-SIM provides mutual authentication. The peer believes that the network is authentic because the network can calculate a correct AT_MAC value in the EAP-Request/SIM/Challenge packet. To calculate the AT_MAC it is sufficient to know the RAND and Kc values from the GSM triplets (RAND, SRES, Kc) used in the authentication. Because the network selects the RAND challenges and the triplets, an attacker that knows n (2 or 3) GSM triplets for the subscriber is able to impersonate a valid network to the peer. EAP-SIM支持双向认证。被认证者相信认证者是因为认证者能计算出正确的AT_MAC,要计算AT_MAC知道RAND和Kc就足够了。因为是认证者选择RAND，攻击者只需知道几个(2-3)Kc就可以假装是一个有效的认证者。 EAP-SIM

Security Claims(安全声明) Auth. mechanism: EAP-SIM is based on the GSM SIM mechanism, which is a challenge/response authentication and key agreement mechanism based on a symmetric 128-bit pre-shared secret. EAP-SIM also makes use of a peer challenge to provide mutual authentication. 认证机理:EAP-SIM基于GSM-SIM的认证机理,它是一种基于挑战/响应的认证和密匙分发机制，需要一个预先共享的128比特长对称密匙(Ki)。EAP-SIM通过被认证者发挑战(NONCE_MT)支持双向认证。 EAP-SIM

Security Claims(安全声明) Ciphersuite negotiation: No Mutual authentication: Yes Integrity protection: Yes Replay protection: Yes Confidentiality: Yes, except method specific success and failure indications Key derivation: Yes Description of key hierarchy:(page 13) Dictionary attack protection: N/A Fast reconnect: Yes Cryptographic binding: N/A Session independence: Yes Fragmentation: No Channel binding: No Indication of vulnerabilities:(page 14,15) EAP-SIM

Using EAP-SIM for WLAN Authentication Example Using EAP-SIM for WLAN Authentication EAP-SIM

Requirements(需求清单) Windows XP built-in supplicant EAP-SIM plug-in for the Windows XP built-in 802.1x Supplicant (http://weap.sf.net) PC/SC compatible smart card reader (QWY LowSpeed CCID smart card reader) Wireless Access Point support RADIUS (TP-LINK TL-WR541G) RADIUS server support EAP-SIM (FreeRadius 1.0.4) EAP-SIM

Network topological diagram (网络拓扑图) simtriplets.dat EAP-SIM

SIM Reader Installation Download the driver from http://agsm.sf.net Insert the USB smart card reader in a USB port,specify the location of the driver. Insert your sim-card into smart card reader,run agsm2.exe to make sure you can access the sim-card. EAP-SIM

Configure freeradius Add the following to clients.conf Download freeradius-1.0.4 from http://www.freeradius.org cd freeradius-1.0.4; Configure;make install; cd src\modules\rlm_sim_files; make install. Add the following to radiusd.conf: In modules {}, add: sim_files { simtriplets = " ${raddbdir}/simtriplets.dat " } in eap{} add sim{} In authorized {}, add: sim_files before eap. Add the following to clients.conf client 192.168.1.0/24 {secret = eap-sim shortname= eap-sim} EAP-SIM

Generate simtriplets.dat Run agsm2.exe. Copy IMSI,RAND,SRES,Kc to simtriplets.dat, at least 5 entries. simtriplets.dat #IMSI RAND SRES Kc 1460001551807128,52632FE305874545AC9936926D796256,8184a227,5F05b4a2CE884400 1460001551807128,ECEB1577E275414e9DD9EF98B277E54A,00fb682e,B6c0de73256c0400 ………… Generate simtriplets.dat Make sure insert 1 The EAP server MAY use the leading "1" as a hint to try EAP-SIM as the first authentication method during method negotiation, rather than for example EAP/AKA. The EAP-SIM server MAY propose EAP-SIM even if the leading character was not "1". EAP-SIM

Configure AP EAP-SIM

EAP-SIM plug-in installation Download wEAP-SIM from http://weap.sf.net Install. Enable tracing. EnableConsoleTracing : set HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\TRACING\ EnableConsoleTracing to nozero set HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\TRACING\ wEAP-SIM\ EnableConsoleTracing to nozero EnableFileTracing: set HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\TRACING\ wEAP-SIM\ EnableFileTracing to nozero EAP-SIM

Authenticate the client EAP-SIM

References http://www.intel.com/technology/itj/2005/volume09issue01/art07_next_generation/p05_simpl_network.htm draft-haverinen-pppext-eap-sim-16.txt [RFC3748] Extensible Authentication Protocol (EAP) S5.Brumley-comp128.pdf [GSM Cloning] http://www.isaac.cs.berkeley.edu/isaac/gsm.html EAP-SIM

问题 & 讨论 EAP-SIM