Wireless Network Security for Future Internet Yasuo Okabe Academic Center for Computing and Media Studies Kyoto University

Overview What is Network Security? W-LAN Security Technologies Security Issues on Public Wireless Internet Access Services Location Privacy Summary

1. What is Network Security? a brief introduction

What is Network Security? sender message recipient adversary? interruption eavesdropping masquerade fabrication modification

Active Attacks and Passive Attacks Interruption denial of service (DoS) Masquerade Fabrication replay Modification Passive Attacks Eavesdropping (or Wiretapping) get the content of messages without the sender/recipient being aware of it Monitoring observe who sends a message to whom at when Passive attacks are more difficult to detect than active attacks

Repudiation ? ? sender message recipient adversary? The sender denies the fact he have sent the message The sender tells a lie. The recipient tells a lie. An adversary fabricated the message. The recipient denies the fact she have received the message An adversary masqueraded as the recipient. The received message is different from what is sent. The sender tells a lie The recipient tells a line An adversary modified it. ｝Both It is meaningless one can believe firmly the opponent tells a lie but he cannot prove it to a third person.

Network Security Attributes in Computer Security Authentication Confidentiality Integrity Availability Authentication confirm both the sender and the recipients surely have the authority to do the act a the communication Nonrepudiation prevent either the sender or the recipient from denying the communication When a message is sent, the recipient can prove that the message is sent from the sender, and vice versa. Concealment assure to be kept unnoticed the fact communication is done between the sender and the recipients to others

2. W-LAN Security Technologies

Wireless LAN IEEE802.11 Wi-Fi (Wireless Fidelity) A set of standards for wireless local area networks (W-LAN) Developed by IEEE LAN/MAN Standards Committee (IEEE802). IEEE 802.11 (1997), 11b (1999), 11a (1999), 11g(2003) IEEE 802.11i (2004) Wi-Fi (Wireless Fidelity) A family of related specifications based on IEEE802.11 but slightly modified. Specified by Wi-Fi Alliance

W-LAN Security Access Control at Access Points Stealth ESSID stop announcement of ESSID (Extended Service Set ID) But, ESSID can be sniffed by monitoring. MAC Address Registration deny packets from a client whose MAC addresse is not registerred But, MAC addresses can be sniffed and be spoofed. WEP, WPA, … 〔T.B.D. later〕 Restriction at Access Points IP address restriction／port filtering Disabling direct communication among clients

WEP (Wired Equivalent Privacy) Authentication and Encryption by a WEP Key 64bit WEP (40bit key＋24bit IV) 128bit WEP (104bit key＋24bit IV) Two mode of authentication Open System authentication No actual authentication at association, but data is encrypted by WEP key Shared Key authentication Four-way challenge-response handshake at association

WEP Encryption Details CRC32 Data (plain text) ICV (Integrity Check Value) RC4 XOR (exclusive OR) WEP key Key stream IV (Initial Vector) (encrypted) MAC header IV Data (encrypted) ICV FCS (Frame Check Sum) IV and hence key stream are frequently changed, so as to protect against brute-force attack.

Vulnerability of WEP Relatively shortness of IV Key remains static 224 ≒ 16,000,000 The same number of packets may be sent only in 10 minutes in 54Mbps W-LAN. Crackers can get the XOR of plain-text data if he find two frames with the same IV (D1+K) + (D2+K) = D1+D2, where D1 and D2 are original data and K is the key stream. Key remains static sometimes yearly… RC4 is known to be weak. Note that cracking can be done passively

Cracking Tools AirSnort Aircrack-ng http://airsnort.shmoo.com/ http://www.aircrack-ng.org

demo

WPA (Wi-Fi Protected Access) WPA-TKIP Improvement of WEP Use a temporal key instead of WEP key Key is assigned per client, per association and periodically changed TKIP: Temporal Key Integrity Protocol Key stream is generated by RC4 from 48bit IV (initial vector) avoid reuse same IV. WPA-AES Use of AES (Advanced Encryption Standard) instead of RC4.

WPA-PSK WPA-PSK (Pre-Shared Key) Weakness Replacement of WEP Initial association between AP and client is done with a pass phase as a pre-shared key Weakness Attacker who have the pre-shared key can eavesdrop all packets. Dictionary attack may succeed if the pre-shared key is not choose enough long and not guessable.

WPA-EAP EAP (Extensible Authentication Protocol) EAP-TLS Authentication based on 802.1x with a Radius authentication server EAP-TLS Based on PKI Server and client mutually authenticate by certificates EAP-PEAP ID/Password based Use of PKI is optional MS-CHAP v2 Server and client mutually authenticate via ID/password EAP-SIM Using SIM (GSM Subscriber Identity Module) Corresponding Node Authentication Server Access Point Mobile Node

Comparison of IEEE802.1X EAP-TLS EAP （Extensible Authentication Protocol) 方式 Client Authentication Server Authentication Security Level Operation Cost EAP-TLS Certificate High EAP-TTLS ID/Password Mid. EAP-PEAP LEAP Low EAP-MD5 ---

How to use EAP-TLS based on PKI Application Server (web) RA CA RA Administrator Apply CA Administrator Authority Delegation Smart Card Identify Authorize User RA Operator Admin Server (web) Issue Request Issue Certificate LDAP RADIUS AP

OpenWRT http://openwrt.org/ Alternative firmware for commodity W-LAN routers Supports many platforms, including Buffalo’s products Open source based on Linux CLI Supports many features like 802.1x with Radius, VPN, etc. Customizable by users themselves. DD-WRT http://www.dd-wrt.com/wiki/ A branch of OpenWRT GUI

3. Security Issues on Public Wireless Internet Access Service

Status of public wireless Internet access Remarkably rapid deployment of IEEE802.11b/g W-LAN in these 10 years Now almost all Note PCs have W-LAN build in. Security risks/incidents have become a social problem. “Public wireless LAN” or “wireless HotSpot” Public Internet Access Service using W-LAN technology Attracts attention of the mass media. In U.S. Bankruptcy of MobileStar (2001) In Japan Paid services are not necessarily satisfactory MIS stops the service （2002） Livedoor Wireless canceled the plan of extending the coverage Each of NTT group company provides service in unsystematic way. HOTSPOT (NTT.com), M-Zone (NTT DoCoMo), Wireless LAN Club (NTT BP), FletsSpot (NTT East/West)

Difficulty in the business model of public wireless Internet access service Issues in cover area Conflict among service providers at public hot spots like railway stations, airports, hotels Number of channels of IEEE802.11b/g is very small In most places only one service available Users who subscribes the service can use it. Most of the spots are located at metropolis, few in local cities. Covers only spots, not area Enormous investment is needed to cover area, compared to 3G mobile phone service Several projects conducted by local governments are suspended in U.S.

Free Wireless Services FON http://www.fon.com Google WiFi http://wifi.google.com eduroam http://www.eduroam.org FreeSpot http://www.freespot.com

Google WiFi A free wireless Internet service in Mountain View by Google More than 400 APs. Service area: almost the whole areal of 18km2 Unique user：15,000/month “We're offering to the city of Mountain View as part of our ongoing efforts to reach out to our hometown.” http://wifi.google.com/city/mv/apmap.html

eduroam W-LAN roaming architecture among academic and research institutes in Europe and other countries. IEEE802.1x (EAP-TTLS)＋raduis federation Roaming between commercial service providers in Europe (experimental)

Is FREE service really possible? We already have Internet Infrastracuture. Most of office/shops/houses have broadband access. ADSL (1～10Mbps) ⇒ FDDH (100Mbps～1Gbps) Providing it to visitors is feasible We rarely consumes the bandwidth fully Wireless service needs little cost. The issue is security Risk of providing network access to unknown visitors Access to the private network can be prohibited but Malicious access to the Internet is hard to limit

Security in public wireless Internet services What is the difference between W-LAN and public Wireless Access? For users: Eavesdropping, MIM (man-in-the-middle) attack Masquerading (Impersonation) For host people of access points Accounting (in paid service only) Avoiding anonymous use

Limitation of Wireless-LAN authentication and encryption technologies for public wireless service Stealth ESSID? ESSID must be announced to public MAC address filtering Can very easily be spoofed Issues in scalability WEP (encryption) Pre-shared key The key is shared by all users WPA-EAP IEEE802.1x Cannot be used in public services. Encryption is done only in Wireless section (between AP and client)

ISP type W-LAN service Features Centralized Management by ISP Wireless AP and Access Network are owned by ISP ISP manages Authentication Server and issues acounts Subscriber must rely on ISP Issues Contract is needed between the ISP and subscribers Corresponding Node ISP Network Authentication Server Access Point 1. 2. AS: authentication server AP: access point MN: mobile node CN: corresponding node Authorization Data Mobile Node

Wireless Internet Service by a single ISP MN (mobile node) Auth Server AP (Access Point) ISP Internet CN (corresponding node) Mutual Authentication ISP’s private network Mutual trust relation

WLAN roaming among ISPs CN Internet (exapmple) iPass eduroam Home ISP AAA server Roam ISP Access points Authentication MN Trust relation between Home ISP And Roam ISP is necessary Mutual trust relation

Self-managed model Features Managed typically with one or a few APs, independently Daily operational cost is not so high. Security policy depends on the host person Grass-root deployment is possible Issues Very costly to assure security level as high as the user can be traced when an incident occurs. No protection if the host person has malicious attempt. Corresponding Node 2. Host person’s network Access Point (1.) Mobile Node

Self-managed FreeSpot （Free Service） CN Internet Host person of APs Eavesdrop Masquerade Fabrication AP Malicious adversary Naïve authentication MN Repudiation

Autonomous Distributed Model Comparison of Public WLAN Service Models Autonomous Distributed Model High ISP Model Framework to enhance the security of self-managed network model Security Self-Managed Model Low High Management Cost Low

Autonomous Distributed Model Network of Authentication System Corresponding Node Authentication Server assuming little confidentiality AP host’s Network Access Point Authorization Authentication Data Mobile Node

Categorization of Security Procedures of Autonomous Distributed Public WLAN services Categorize authentication mechanisms based on the following two aspects: Authentication Transaction at Access Point Relayed Passed Through Data Path Tunneling Direct [ Pros and Cons of Four Models ] Authentication Treatment at AP Relayed: Eliminate malformed authentication Make an AP busier Data Path Tunneling: Acquire location privacy of MNs Detour via AS is forced In the other case, pro and con go across. [ Properties and Name of Each Model ] Data Path No Auth. at AP Auth. at AP Tunnel PATP RATP Direct PADP RADP

[ ] [ ] Relayed Authentication, Passed-through Authentication, Tunneling & Authentication Server 2. 4. Corresponding Node Corresponding Node 5. Tunneling Server 2. (Relay of 1.) 1. Access Point 3. Access Point Authorization 1. Authentication VPN Tunnel Data Mobile Node Mobile Node [ ] [ ] Passed-through Authentication, Tunneling Path (PATP) Model Relayed Authentication, Tunneling Path (RATP) Model

[ ] [ ] Passed-through Authentication, Direct Path (PADP) Model Corresponding Node 4. 2. Corresponding Node 3. 3. Authentication Server 1. 2. Authentication Server Access Point Access Point ID Info. Exchange 1. Authentication Data Mobile Node Mobile Node [ ] Passed-through Authentication, Direct Path (PADP) Model [ ] Relayed Authentication Direct Path (RADP) Model

Implementation in MIAKO.net CN Internet VPN server AP Pass through but VPN protocols only AP hosts Users’ own or By ISP MN Mutual trust relation

4. Location Privacy

What is Location Privacy? Location privacy is the combination of information of when and where you are, and who you are Your location privacy is expected to be disclosed to neither of corresponding node authentication server access point Trade off with Anonymity v.s. security Location-aware service Authentication Server Corresponding Node Access Point Mobile Node You are here!

Location privacy in ISP type W-LAN service The authentication server knows who you are where you are now To whom you are communicating Users are forced to rely on the service provider Mobile phone carriers does. Corresponding Node Authentication Server Access Point 1. 2. Authorization Mobile Node Data

Location Privacy in Roaming Service Authentication Server Corresponding Node Authentication server knows who you are where you are Access point may know to whom you are communicating Corresponding node will know where the MN is Access Point Mobile Node

How pseudonym conceals location privacy in roaming service Home ISP Authentication Server Access point may know where you are to whom you are communicating which is your home ISP, not who you are Authentication server may know who you are which roam ISP you are using, not where you are Corresponding Node Roam ISP Access Point Authentication proxy server Access with pseudonym Mobile Node

Location privacy in VPN-based Tunneling Path Model Home ISP Authentication server knows who you are where you are Access point cannot know to whom you are communicating Corresponding node cannot know where the MN is Corresponding Node Tunneling Server Access Point Roam ISP Authorization VPN Tunnel Data Mobile Node

5. Summary

Summary Security issues of W-LAN roaming services Proposal of autonomous distributed public wireless Internet access architecture MIAKO.net A service model for implementing ubiquitous networking with a grass-root W-LAN roaming with enough security.

Categorized security problems of public WLAN services [ Concluding Remarks ] Categorized security problems of public WLAN services Proposed an Autonomous Distributed public WLAN service model Compared some security procedures of Autonomous Distributed public WLAN service Each procedure has its pros and cons therefore we cannot say which is the best for future use MIAKO.NET public wireless service This is based on PATP model [ References ] A. Balanchandran et al., ‘Wireless Hotspots: Current Challenges and Future Cirections’, 2003 N. Borisov et al., ‘(In)Security of the WEP Algorithm’, 2001 D. Golombek, ‘Single Computer Breaks 40-bit RC4 in under 8 Days’, 1996 T. Komura et al., ‘The MIAKO.NET Public Wireless Internet Service in Kyoto’, 2003 Y. Matsunaga et al., ‘Secure Authentication System for Public WLAN Roaming’, 2003 L. Ackerman et al., ‘Wireless Location Pricay: Low and Policy in the U.S., EU and Japan’, - ISOC Member Brefing, 2003