Wireless Network Security for Future Internet

Yasuo OkabeAcademic Center for Computing and Media Studies

Kyoto University

Overview

1. What is Network Security?

2. W-LAN Security Technologies

3. Security Issues on Public Wireless Internet Access Services

4. Location Privacy

5. Summary

1. What is Network Security?a brief introduction

What is Network Security?

sender recipient

message

interruption eavesdropping

masquerade fabrication modification

adversary?

Active Attacks and Passive Attacks

• Active 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

• 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– The sender tells a lie.– The recipient tells a lie.– 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.

senderrecipient

message

｝ Both

adversary?

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– Confidentiality– Integrity– Availability

Concealment•assure to be kept unnoticed the fact communication is done between the sender and the recipients to others

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.

2. W-LAN Security Technologies

Wireless LAN

• IEEE802.11– 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 regist

erredBut, 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

WEP key

IV

Key stream

RC4

Data (plain text) ICV

CRC32

(Integrity Check Value)

XOR (exclusive OR)

Data (encrypted) ICV

(encrypted)

MAC header IV FCS (Frame Check Sum)

(Initial Vector)

IV and hence key stream are frequently changed, so as to protect against brute-force attack.

Vulnerability of WEP

• Relatively shortness of IV– 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– http://airsnort.shmoo.com/

• Aircrack-ng– 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)– 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)

• 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)

Mobile Node

AccessPoint

CorrespondingNode

AuthenticationServer

Comparison of IEEE802.1X EAP-TLS

• EAP （ Extensible Authentication Protocol)

方式 Client Authentication

Server Authentication

Security Level

Operation Cost

EAP-TLS Certificate Certificate High High

EAP-TTLS ID/Password Certificate Mid. Mid.

EAP-PEAP ID/Password Certificate Mid. Mid.

LEAP ID/Password ID/Password Low Low

EAP-MD5 ID/Password --- Low Low

TARO SUZUKITARO SUZUKI 08/07

Smart CardCA Administrator

RA Administrator

RA Operator

User

RACA

Apply

IdentifyAuthorize

Issue Certificate

Application Server (web)

Admin Server (web)

Authority Delegation

Issue Request

How to use EAP-TLSbased on PKI

APRADIUSLDAP

OpenWRThttp://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-WRThttp://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 ofpublic 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 whol

e 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 b

y 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

AS: authentication serverAP: access pointMN: mobile nodeCN: corresponding node

Mobile Node

CorrespondingNode

ISPNetwork

AccessPoint

AuthenticationServer

Data

Authorization

1. 2.

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

MN

Access pointsRoam ISP

InternetCN

Authentication

Home ISP

AAA server

(exapmple)•iPass•eduroam

Mutual trust relation

Trust relation between Home ISPAnd Roam ISP is necessary

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 l

evel as high as the user can be traced when an incident occurs.

– No protection if the host person has malicious attempt.

CorrespondingNode

Mobile Node

AccessPoint

Host person’snetwork

(1.)

2.

Self-managed 　 FreeSpot 　（ Free Service ）

MN

AP

Internet

CN

Host person of APs

Naïve authentication

Maliciousadversary

• Eavesdrop• Masquerade• Fabrication

Repudiation

Management CostHigh Low

Self-ManagedModel

ISP Model

AutonomousDistributed

Model

Framework to enhance the security of self-managed network model

Secu

rity

High

Low

Comparison of Public WLANService Models

AP host’sNetwork

Network ofAuthenticationSystem Corresponding

Node

Mobile Node

Access Point

AuthenticationServer

Authentication

Data

Authorization

assuming littleconfidentiality

Autonomous Distributed Model

Data PathNo Auth.

at APAuth. at

AP

Tunnel PATP RATP

Direct PADP RADP

[ Properties and Name of Each Model ]

Categorization of Security Procedures ofAutonomous 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.

CorrespondingNode

Tunneling Server

AccessPoint

Mobile Node

1.

2.

Passed-through Authentication,Tunneling Path (PATP) Model

VPN Tunnel

Authentication

Data

Authorization

Tunneling &Authentication

Server

Corresponding Node

AccessPoint

Mobile Node

3.

2. (Relay of 1.)

4.

5.

1.

Relayed Authentication,Tunneling Path (RATP) Model[ ][ ]

Authentication

Data

ID Info. Exchange

AuthenticationServer

CorrespondingNode

Mobile Node

AccessPoint

1.3.

2.

Passed-through Authentication,Direct Path (PADP) Model

Mobile Node

AccessPoint

CorrespondingNode

AuthenticationServer

1.

2.

3.

4.

Relayed AuthenticationDirect Path (RADP) Model[ ] [ ]

Implementation in MIAKO.net

MN

AP

Internet

CN

AP hostsUsers’ ownor

By ISP

VPNserver

Mutual trust relation

Pass throughbut VPN protocols only

4. Location Privacy

What is Location Privacy?

• Location privacy is the combination of information of when and where you are, an

d who you are• Your location privacy is e

xpected to be disclosed to neither of– corresponding node– authentication server– access point

• Trade off with– Anonymity v.s. security– Location-aware service

CorrespondingNode

Mobile Node

Access Point

AuthenticationServer

You are here!

Location privacy inISP 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. Mobile Node

CorrespondingNode

AccessPoint

AuthenticationServer

Data

Authorization

1. 2.

CorrespondingNode

Mobile Node

Access Point

AuthenticationServer

Location Privacy in Roaming Service

•Authentication server knows• who you are• where you are

•Access point may know• where you are• who you are• to whom you are communicating

•Corresponding node will know• where the MN is

CorrespondingNode

Mobile Node

Access Point

AuthenticationServer

How pseudonym conceals location privacyin roaming service

•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

Access with pseudonym

Authentication proxy server

Home ISP

Roam ISP

CorrespondingNode

Tunneling Server

AccessPoint

Mobile Node

Location privacy in VPN-basedTunneling Path Model

VPN Tunnel

Data

AuthorizationRoam ISP

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

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 n

etworking with a grass-root W-LAN roaming with enough security.

[ 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