Security Issues in Mobile
WiMAX(IEEE 802.16e)
Frank, A Ibikunle
Covenant University, Electrical and
Information Engineering Department, Ota.
2009 IEEE Mobile WiMAX Symposium
Wimax
☺802.16x
☺802.16d (fixed)
☺802.16e (mobile)
☺802.16e ----3G : 韓國(WiBro), 美國, 中
國大陸(專利)
☺802.16m ---- 4G : 起步
台灣與全球
頻譜與執照
北區 南區 全區
全球
Map: http://www.wimaxmaps.org/
和WiFi的不同
http://www.youtube.com/watch?v=chlG
qhRKVjQ
基本名詞
Ớ Main roles involved in 802.16:
Ớ Base Station (BS)
Ớ Mobile Station (MS) / Subscriber Station (SS)
Ớ Two security protocols of interest:
Ớ Authentication/Authorization protocol,
establishes a shared Authorization Key (AK)
Ớ 3-way Traffic Encryption Key (TEK)
Handshake
Ớ AK used to derive various other keys
Ớ Traffic Encryption Keys are used to
encrypt message data between the BS
and MS
Ớ KEK: key encryption key
Ớ MBS: Multicast and Broadcast Service
3-way TEK Handshake
After authentication, BS initiates a 3-way
handshake to transfer TEKs to MS
TEKs generated by BS
Have a specified lifetime, after which new TEK
is requested by MS
Structure of the 3-way handshake:
Challenge: BS → MS
Request:
MS → BS
Response: BS → MS
Define
Security: protection of data being
transmitted over a wireless networks.
CIA
Confidentiality: Allowing only that the
intended legitimate recipients to read
encrypted messages(information).
Integrity: is referred to as ensuring that
another party has not altered messages
after it has been sent.
Authentication: This is making sure that
parties sending messages or receiving
messages are who they say they are, and
have the right to undertake such actions.
On wired networks:
VPNs
IPSec
IDS
Firewalls…
Major Problem
Securing wireless signal is in its mode of
transmission communicated through the
air.
802.16e provides 2
authentication
RSA
加密演算法: 因數分解
難度和bits有關
EAP(Extensible Authentication Protocol)
EAP
常用在無線網路
Data link layer
Packet
An authentication framework: only define
message format and has many methods.
Using EAP can define a way to encapsulate
EAP messages.
Provides some common functions and
negotiation of authentication methods
called EAP methods.
MAC
Message Authentication Code
Like Digital Signature, but using
symmetry key.
Initial network
1. EAP-based authentication.
2. The BS and BS set up a common AK.
3. KEK is derived from the AK. (and AK is
used to securely transfer further keys)
4. MAC digest and the transferred TEK is
encrypted by the KEK.
5. After above, the 3-way TEK-exchange for
each data connection is executed.
AK – KEK - TEK
Security Flaws
1. Unauthenticated messages
2. Unencrypted management
communication
3. Shared keys in Multicast and Broadcast
Service
Unauthenticated messages
Most of the management messages defined in
IEEE 802.16e are integrity protected.
Done by:
HMAC: Hash based message authentication
code
CMAC: Cipher based message
authentication code
But some messages are not covered by any
authentication mechanism.
Unauthenticated messages
MOB_TRF-IND: Traffic Indication message
MOB_NBR-ADV: Neighbor Advertisement message
FPC: Fast Power Control message
MSC-REQ: Multicast Assignment Request message
DBPC-REQ: Downlink Burst Profile Change Request
message
6. PMC-REQ:
7. MOB_ASC-REP: Association Result Report
8. RNG-REQ: Ranging Request message
1.
2.
3.
4.
5.
Unencrypted management
communication
In Mobile WiMAX management messages are
still sent in the clear.
Nearly all management information exchanged
between MS and BS can be accessed by a
listening adversary.
Collecting management info can create detailed
profiles about MSs.
Including capabilities of devices, security settings,
associations with base stations…
Also can determine the movement and
approximate position of the MS.
Shared keys in Multicast and
Broadcast Service
Encrypted symmetrically with a shared
key.
Also message authentication is based on
the same shared key.
This alg. Contains the vulnerability that
every group member can also encrypt
and authenticate broadcast messages as
if they originate from the real BS(be
forged).
Shared keys in Multicast and
Broadcast Service
GTEK: Group TEK
MBRA: Multicast and Broadcast Rekeying
Algorithm
The Solutions
1.
For Unauthenticated messages:
1. Easily using a HMAC or CMAC digit as well.
2. But most messages are very short, a tradeoff
between the security and the effectiveness of the
protocol has to be found.
3. Suggestion: use CMAC and Short HMAC to 64bits,
and with all other needed parameters (i.e., packet
number, key sequence number and reserved
fields), both will be 104 bits in total.
HMAC
詳細請看:
http://en.wikipedia.org/wiki/HMAC
Use SHA-1 (128bits ?)
SHA: Secure Hash Algorithm
CMAC
詳細請看:
http://en.wikipedia.org/wiki/CMAC ,
too.(有點複雜......)
Use AES-128 (感覺也很偉大……)
AES: Advanced Encryption Standard
A symmetric-key encryption standard
adopted by the U.S. government.
2. For Unencrypted management
communication:
1. Encrypt directly after both sides have
established a common key.
2. Doesn’t introduce any overhead to the
connection.
3. Possible to use a symmetric key,
decryption can be processed very fast.
3. For broadcasted/multicasted
messages(shared keys):
1. From outside the group.
2. Use asymmtric cryptography(but may not
effective).
3. And for the MBS, see Figures as followings.
Figure 1. Possible solutions to
transmit GTEK in a secure way
Figure 2. Avoiding key forgery by
a GTEK hash chain
Contributions
1. Describe different security
vulnerabilities found in IEEE 802.16e.
2. Proffer possible solutions to eliminate
them.
Thanks
Q&A