New Challenges in Securing our
Communication Infrastructure
Wade Trappe
Agenda

Wireless Overview
– State of the Wireless Union: Where are we?
– Vision for 4G

Security Challenges for Future Wireless Networks:
– 3G Multicast Security
– Authentication in Broadcast Environments
– Security in Ad Hoc Networks
– Biologically-Inspired Self-Healing Frameworks
– Networks of Networks Security Issues
State of the Wireless Union

We are still waiting for third
generation (3G) wireless.
WLAN (Wi-Fi) technologies are
rapidly growing:
– Estimated $800 Million in US sales
for 2004

Prices for Wi-Fi equipment
plummeting
– $100 access point, $70 WLAN card

New, unregulated networks
popping up everywhere
– Its not just Starbucks & T-Mobile
– Open-access hotspots

Warchalking is now a common
hobby
Global Wi-Fi Growth
Sales ($ Million)

1000
800
North America
600
Asia
400
Europe
200
0
1
2
3
4
5
6
Year
Source: Allied Business Intelligence
Vision for the Fourth Generation

Wireless devices will continue to drop in price
– Wireless sensors will be deployed everywhere
– Ability to monitor everything, from temperature to traffic
– Remote sensing and autonomic living applications

Next generation wireless systems (4G) will seek to facilitate mass market
services with new network architecture:
– Self-organizing, ad-hoc wireless access networks: Ad-hoc wireless network
protocols which support multihop and peer-to-peer service models, particularly
for low-tier uses (in-home, sensors, etc.)
– Networks of networks: Future wireless networks will support co-existence of
multiple types of networks

Security will be a critical issue:
– Unregulated networks will provide an untraceable platform to launch network
attacks
– Mobility and power-efficiency are still concerns
3G Multicast Security
Radio Network Subsystem (RNS)
UMTS Core Network
RNC
SGSN
Node B
GGSN
Node B
BMSC
Node B
Internet
UMTS Terrestrial Radio Access Network




Keys must be shared by multicast group participants
As users join and leave, keys must be changed
3GPP has proposed a new entity, the BMSC for managing broadcast and
multicast services
The BMSC can perform key management
3G Multicast Security

3GPP currently is investigating
several multicast frameworks

To optimize key management,
one should match the key tree to
underlying multicast topology

3GPP has not decided on a
multicast topology

We are examining the
performance of multicast key
management at the BMSC for
different 3G multicast scenarios

Examine the issue of key
management during handoff
between node-B’s and RNCs
Prototype Secure Chat Application has
been developed
•Server is implemented in J2SE
•Clients are implemented in J2ME
Broadcast/Multicast Authentication

Important challenge facing secure multicast communication is
data authentication:
– Ensures data is from trusted source
– Ensures data was not modified en route

Unicast Data Authentication uses standard cryptographic
techniques:
– Digital Signatures: (RSA, DSA)

Drawbacks: Inefficient due to:



Large per packet computation
Large communication overhead
Note: Drawbacks are not critical in many applications.
– Message Authentication Codes (MAC): (HMAC-MD5)


Class of symmetric keyed one-way hash function
Advantages:



Computationally efficient
Compressed code
Computationally non-invertible
Multicast Authentication

Multicast source authentication is more complex than unicast:
– Symmetric Key Cryptography cannot be used


Key is known to all receivers
Packets can be forged by any receivers
– Asymmetric key cryptography is required
– Lost packets are not retransmitted

Digital signature schemes provide good authentication:
– Each message is signed by appending digital signature
– Significant drawbacks for realtime, low-power multicast applications:


Time-to-sign and time-to-verify
Bandwidth and overhead.

We want a technique that will take advantage of both

One approach: Delayed key disclosure
Multicast Authentication

Delayed Key Disclosure: (e.g. TESLA)
All Packets Authenticated with
K1 have arrived to all group members
Keys
K1
K2
K3
K4
Reveal
K1
Reveal
K2
K5
Time
Auth PacketsAuth PacketsAuth PacketsAuth Packets
Auth Packets
with K1
with K2
with K3
with K4 with K5

Weakness:
– Use of buffers allows for a simple denial of service (DoS) attack
– Since there is no way to check packets until key is disclosed, buffer will
overflow

How to protect against DoS attacks?
DoS Resistant TESLA

Idea: Use multiple keys and stagger the delayed key disclosure
scheme.
Reveal
Ki-3
Keys
Reveal
Ki-1
Reveal
Ki-2
Ki
Ki+1
Ki+2
M1
M2
M3
MACKi
MACKi+1
MACKi+2
MACKi-1
MACKi
MACKi+1
MACKi-2
MACKi-1
MACKi
End result:
• Provides a filter to remove packets from buffer
before the maximum network delay is achieved
Reveal
Ki
Ki+3
Reveal Reveal
Ki+1
Ki+2
Ki+4
Time
Ki-2
P1
Ki-1
P1
P1
Ad-Hoc Network Security

Ad-hoc networks introduce new security challenges
– Evolving authentication: Nodes are moving, and clusters are constantly being
redefined.
– Secure routing: New types of attacks (e.g. wormhole attacks) exist.
– Service non-repudiation: No proof that a service (QoS) was provided.

WINLAB approach: Develop a hierarchical, self-organizing network
– Can nodes develop an evolving trust model? Elected nodes give trust certificates.
Internet
BTS
AP
WLAN
micro-cell
Access Point
Forwarding node
FN
3G cell
low-tier
(e.g. sensor)
user nodes
personal-area
pico-cell
Authentication in Hierarchical
Ad Hoc Sensor Networks

Public key certificates are not
suitable for flat ad hoc networks
– To check certificate requires
expensive public key operations

AP
Three tier architecture:
– Varying levels of computational
FN
power within the sensor network
– Sensors do not communicate with
SN
each other
– Forwarding nodes are radio-relay  Authentication framework:
– Access points provide filter to
 TESLA Certificates
application
– Alternative to PK certificates
– TESLA certificates provide efficient
– Uses symmetric key cryptography
sensor node handoff
– Delayed key disclosure
– Weak and assured data
authentication provided
Self-Healing Wireless Networks

Ad hoc networks are being
deployed for a broad variety of
applications, and are a key
platform for:
– Remote sensing applications
(Homeland Security)
– Military battlefield networks
– Mesh networks and ubiquitous
content distribution

Challenge: These networks are
not tolerant to active or passive
faults:
– Nodes are cheap and will
often malfunction
– Nodes are in an open
environment and vulnerable to
being captured by adversaries
Network Node
Corrupted Network Node
Self-healing framework



In nature, we have many cases where systems get infected and
must repair themselves
Ad hoc networks should emulate nature and heal themselves!
Model: Human immune system
– Leuocytes (white blood cells): There are two types, those that
develop in lymph nodes and those that develop in bone marrow
– Killer T-cells: Destroy antigens either by themselves, or by
recruiting other white blood cells
– Lymphocytes: Produce antibodies, that seek to surround and
cover an antigen, rendering it harmless until a phage can arrive to
destroy the neutralized antigen
– Chemotaxis: Leuocytes find their way to an antigen by following
a chemical trail of “bread crumbs”
Mobile Agent Framework

Biologically-inspired selfhealing security framework
– Mobile Code will launch
from network lymph nodes
to patrol network
– Mobile Code will leave
behind tags allowing for the
process of network
chemotaxis
– In response, Repair and
Destroy Agents will be
launched to reboot, or shut
down malfunctioning nodes
via secure OS environment
Network Node
Network Lymph Node
Corrupted Network Node
Enabling Technologies

Enabling Technologies to be Researched:
– Smart Messages (SMs): Migratory execution units that execute
on ad hoc nodes, and will form the different types of mobile agents
involved in a network immune system
– Trajectory Routing: Self-routing mechanisms for mobile code
capable of finding fast and efficient route to faulty node
– Anomaly Detection: Statistical and policy-based detection
mechanisms for identifying faulty network nodes
– Flexible Security Policies: Describe how the network immune
system responds to different types of corruptions or threats
– Authorization and Secure OS: Each node must have a secure
environment from which mobile agents perform their functions
“Network of Wireless Networks” Security
Internet-like architecture
that promotes organic
growth...
Global Internet
Mobility supporting Internet
wired links
high-tier
devices
(mobile
terminals)
Radio Access
Network
(cellular)
radio link
microcell
med-tier
devices
(laptops, PDA’s)
picocell
low-tier
devices
(home, sensors)
Security Needs:
•Certification across
networks
•Security must scale to
multiple simultaneous
platforms!