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

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

3. 1. What is Network Security? a brief introduction

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

5. 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

6. 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.

7. 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

8. 2. W-LAN Security Technologies

9. 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 (1997), 11b (1999), 11a (1999), 11g(2003)
IEEE i (2004)
Wi-Fi (Wireless Fidelity)
A family of related specifications based on IEEE but slightly modified.
Specified by Wi-Fi Alliance

10. 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

11. 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

12. 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.

13. 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

14. Cracking Tools AirSnort Aircrack-ng http://airsnort.shmoo.com/

15. demo

16. 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.

17. 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.

18. 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

19. 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
---

20. 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

21. 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
A branch of OpenWRT
GUI

22. 3. Security Issues on Public Wireless Internet Access Service

23. 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)

24. 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.

25. Free Wireless Services
FON
Google WiFi
eduroam
FreeSpot

26. 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.”

27. 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)

28. 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

29. 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

30. 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)

31. 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

32. 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

33. WLAN roaming among ISPsCN
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

34. 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

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

36. 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

37. 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

38. 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

39. [ ] [ ] 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

40. [ ] [ ] 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

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

42. 4. Location Privacy

43. 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!

44. 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

45. 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

46. 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

47. 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

48. 5. Summary

49. 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.

50. 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