Security and Misbehavior Handling in
Wireless Ad Hoc Networks
Nitin H. Vaidya
University of Illinois at Urbana-Champaign
nhv@uiuc.edu
http://www.crhc.uiuc.edu/~nhv
© 2005 Nitin Vaidya
1
Notes

Coverage not exhaustive. Only a few example schemes discussed

Only selected features of various schemes are typically discussed.
Not possible to cover all details in this tutorial

Some protocol specs have changed over time, and the slides may
not reflect the most current specifications

Jargon used to discuss a scheme may occasionally differ from that
used in the original papers

Names in brackets, as in [Xyz00], refer to a document in the list of
references

Abbreviation MAC used to mean either Medium Access Control or
Message Authentication Code – implied meaning should be clear
from context
2
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
3
Mobile Ad Hoc Networks (MANET)
4
Mobile Ad Hoc Networks

Formed by wireless hosts which may be mobile

Without (necessarily) using a pre-existing
infrastructure

Routes between nodes may potentially contain
multiple hops
5
Mobile Ad Hoc Networks

May need to traverse multiple links to reach a
destination
B
A
C
D
6
Mobile Ad Hoc Networks (MANET)

Mobility causes route changes
A
B
C
D
7
Why Ad Hoc Networks ?

Ease of deployment

Speed of deployment

Decreased dependence on infrastructure
8
Many Applications




Personal area networking
cell phone, laptop, ear phone, wrist watch
Military environments
soldiers, tanks, planes
Civilian environments
taxi cab network
meeting rooms
sports stadiums
boats, small aircraft
Emergency operations
search-and-rescue
policing and fire fighting
9
Many Variations

Fully Symmetric Environment
all nodes have identical capabilities and responsibilities

Asymmetric Capabilities
transmission ranges and radios may differ
battery life at different nodes may differ
processing capacity may be different at different nodes
speed of movement

Asymmetric Responsibilities
only some nodes may route packets
some nodes may act as leaders of nearby nodes (e.g.,
cluster head)
10
Many Variations

Traffic characteristics may differ in different ad hoc
networks
bit rate
timeliness constraints
reliability requirements
unicast / multicast / geocast
host-based addressing / content-based addressing /
capability-based addressing

May co-exist (and co-operate) with an infrastructurebased network
11
Many Variations

Mobility patterns may be different
people sitting at an airport lounge
New York taxi cabs
kids playing
military movements
personal area network

Mobility characteristics
speed
predictability
• direction of movement
• pattern of movement
uniformity (or lack thereof) of mobility characteristics among
different nodes
12
Challenges








Limited wireless transmission range
Broadcast nature of the wireless medium
Hidden terminal problem (see next slide)
Packet losses due to transmission errors
Mobility-induced route changes
Mobility-induced packet losses
Battery constraints
Potentially frequent network partitions
Ease of snooping on wireless transmissions (security
hazard)
13
Hidden Terminal Problem
A
B
C
Nodes A and C cannot hear each other
Transmissions by nodes A and C can collide at node B
Nodes A and C are hidden from each other
14
Research on Mobile Ad Hoc Networks
Variations in capabilities & responsibilities
X
Variations in traffic characteristics, mobility models, etc.
X
Performance criteria (e.g., throughput, energy, security)
=
Significant research activity
15
The Holy Grail

A one-size-fits-all solution
Perhaps using an adaptive/hybrid approach that can adapt
to situation at hand

Difficult problem

Many solutions proposed trying to address a
sub-space of the problem domain
16
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
17
Unicast Routing
in
Mobile Ad Hoc Networks
18
Why is Routing in MANET different ?

Host mobility
link failure/repair due to mobility may have different
characteristics than those due to other causes

Rate of link failure/repair may be high when nodes
move fast

New performance criteria may be used
route stability despite mobility
energy consumption
19
Unicast Routing Protocols

Many protocols have been proposed

Some have been invented specifically for MANET

Others are adapted from previously proposed
protocols for wired networks

No single protocol works well in all environments
some attempts made to develop adaptive protocols
20
Routing Protocols

Proactive protocols
Determine routes independent of traffic pattern
Traditional link-state and distance-vector routing protocols
are proactive

Reactive protocols
Maintain routes only if needed

Hybrid protocols
21
Trade-Off

Latency of route discovery
Proactive protocols may have lower latency since routes are
maintained at all times
Reactive protocols may have higher latency because a route
from X to Y may be found only when X attempts to send to Y

Overhead of route discovery/maintenance
Reactive protocols may have lower overhead since routes
are determined only if needed
Proactive protocols can (but not necessarily) result in higher
overhead due to continuous route updating

Which approach achieves a better trade-off depends
22
on the traffic and mobility patterns
Reactive Routing Protocols
23
Routing Protocols

Proactive protocols for ad hoc networks are often
derived from link state or distance vector routing
protocols

But with some optimizations

We will not discuss proactive protocols in detail

Before discussing an example reactive protocol, let
us consider “flooding” as a routing protocol
24
Flooding for Data Delivery

Sender S broadcasts data packet P to all its
neighbors

Each node receiving P forwards P to its neighbors

Sequence numbers used to avoid the possibility of
forwarding the same packet more than once

Packet P reaches destination D provided that D is
reachable from sender S

Node D does not forward the packet
25
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
Represents a node that has received packet P
Represents that connected nodes are within each
other’s transmission range
26
Flooding for Data Delivery
Y
Broadcast transmission
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
Represents a node that receives packet P for
the first time
Represents transmission of packet P
27
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
• Node H receives packet P from two neighbors:
potential for collision
28
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
• Node C receives packet P from G and H, but does not forward
it again, because node C has already forwarded packet P once
29
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
• Nodes J and K both broadcast packet P to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
=> Packet P may not be delivered to node D at all,
despite the use of flooding
30
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
• Node D does not forward packet P, because node D
is the intended destination of packet P
31
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
• Flooding completed
K
I
D
N
• Nodes unreachable from S do not receive packet P (e.g., node Z)
• Nodes for which all paths from S go through the destination D
also do not receive packet P (example: node N)
32
Flooding for Data Delivery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
• Flooding may deliver packets to too many nodes
(in the worst case, all nodes reachable from sender
may receive the packet)
D
N
33
Flooding for Data Delivery: Advantages

Simplicity

May be more efficient than other protocols when rate
of information transmission is low enough that the
overhead of explicit route discovery/maintenance
incurred by other protocols is relatively higher
this scenario may occur, for instance, when nodes transmit
small data packets relatively infrequently, and many topology
changes occur between consecutive packet transmissions

Potentially higher reliability of data delivery
Because packets may be delivered to the destination on
multiple paths
34
Flooding for Data Delivery: Disadvantages

Potentially, very high overhead
Data packets may be delivered to too many nodes who do
not need to receive them

Potentially lower reliability of data delivery
Flooding uses broadcasting -- hard to implement reliable
broadcast delivery without significantly increasing overhead
– Broadcasting in IEEE 802.11 MAC is unreliable
In our example, nodes J and K may transmit to node D
simultaneously, resulting in loss of the packet
– in this case, destination would not receive the packet at all
35
Flooding of Control Packets

Many protocols perform (potentially limited) flooding
of control packets, instead of data packets

The control packets are used to discover routes

Discovered routes are subsequently used to send
data packet(s)

Overhead of control packet flooding is amortized over
data packets transmitted between consecutive
control packet floods

Several protocols based on this (Examples: DSR,
AODV)
36
Dynamic Source Routing (DSR) [Johnson96]

When node S wants to send a packet to node D, but
does not know a route to D, node S initiates a route
discovery

Source node S floods Route Request (RREQ)

Each node appends own identifier when forwarding
RREQ
37
Route Discovery in DSR
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents a node that has received RREQ for D from S
38
Route Discovery in DSR
Y
Broadcast transmission
[S]
S
Z
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents transmission of RREQ
[X,Y]
Represents list of identifiers appended to RREQ
39
Route Discovery in DSR
Y
Z
S
E
[S,E]
F
B
C
A
M
J
[S,C]
H
G
K
I
L
D
N
• Node H receives packet RREQ from two neighbors:
potential for collision
40
Route Discovery in DSR
Y
Z
S
E
F
B
[S,E,F]
C
M
J
A
L
G
H
I
[S,C,G] K
D
N
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
41
Route Discovery in DSR
Y
Z
S
E
[S,E,F,J]
F
B
C
M
J
A
L
G
H
K
I
D
[S,C,G,K]
• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
N
42
Route Discovery in DSR
Y
Z
S
E
[S,E,F,J,M]
F
B
C
M
J
A
L
G
H
K
D
I
• Node D does not forward RREQ, because node D
is the intended target of the route discovery
N
43
Route Discovery in DSR

Destination D on receiving the first RREQ, sends a
Route Reply (RREP)

RREP is sent on a route obtained by reversing the
route appended to received RREQ

RREP includes the route from S to D on which RREQ
was received by node D
44
Route Reply in DSR
Y
Z
S
E
RREP [S,E,F,J,D]
F
B
C
M
J
A
L
G
H
K
I
Represents RREP control message
D
N
45
Route Reply in DSR

Route Reply can be sent by reversing the route in
Route Request (RREQ) only if links are guaranteed
to be bi-directional
To ensure this, RREQ should be forwarded only if it received
on a link that is known to be bi-directional

If unidirectional (asymmetric) links are allowed, then
RREP may need a route discovery for S from node D
Unless node D already knows a route to node S
If a route discovery is initiated by D for a route to S, then the
Route Reply is piggybacked on the Route Request from D.

If IEEE 802.11 MAC is used to send data, then links
have to be bi-directional (since Ack is used)
46
Dynamic Source Routing (DSR)

Node S on receiving RREP, caches the route
included in the RREP

When node S sends a data packet to D, the entire
route is included in the packet header
hence the name source routing

Intermediate nodes use the source route included in
a packet to determine to whom a packet should be
forwarded
47
Data Delivery in DSR
Y
DATA [S,E,F,J,D]
S
Z
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Packet header size grows with route length
48
When to Perform a Route Discovery

When node S wants to send data to node D, but does
not know a valid route node D
49
Route Error (RERR)
Y
RERR [J-D]
S
Z
E
F
B
C
M
J
A
L
G
H
K
I
D
N
J sends a route error to S along route J-F-E-S when its attempt to
forward the data packet S (with route SEFJD) on J-D fails
Nodes hearing RERR update their route cache to remove link J-D
50
Unicast Routing Protocols

We will use DSR as the example routing protocol in
much of our discussion
51
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
52
Medium Access Control Protocols
53
Medium Access Control

Wireless channel is a shared medium

Need access control mechanism to avoid
interference

MAC protocol design has been an active area of
research for many years [Chandra00]
54
MAC: A Simple Classification
Wireless
MAC
Centralized
Distributed
Guaranteed
or
controlled
access
Random
access
IEEE 802.11
55
Hidden Terminal Problem




Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B, C cannot detect the
transmission using the carrier sense mechanism
If C transmits, collision will occur at node B
A
B
C
56
MACA Solution for Hidden Terminal Problem
[Karn90]

When node A wants to send a packet to node B,
node A first sends a Request-to-Send (RTS) to A

On receiving RTS, node A responds by sending
Clear-to-Send (CTS), provided node A is able to
receive the packet

When a node (such as C) overhears a CTS, it keeps
quiet for the duration of the transfer
Transfer duration is included in RTS and CTS both
A
B
C
57
Reliability

Wireless links are prone to errors. High packet loss
rate detrimental to transport-layer performance.

Mechanisms needed to reduce packet loss rate
experienced by upper layers
58
A Simple Solution to Improve Reliability

When node B receives a data packet from node A,
node B sends an Acknowledgement (Ack). This
approach adopted in many protocols
[Bharghavan94,IEEE 802.11]

If node A fails to receive an Ack, it will retransmit the
packet
A
B
C
59
IEEE 802.11 Wireless MAC

Distributed and centralized MAC components
Distributed Coordination Function (DCF)
Point Coordination Function (PCF)

DCF suitable for multi-hop ad hoc networking

DCF is a Carrier Sense Multiple Access/Collision
Avoidance (CSMA/CA) protocol
60
IEEE 802.11 DCF

Uses RTS-CTS exchange to avoid hidden terminal
problem
Any node overhearing a CTS cannot transmit for the
duration of the transfer

Uses ACK to achieve reliability

Any node receiving the RTS cannot transmit for the
duration of the transfer
To prevent collision with ACK when it arrives at the sender
When B is sending data to C, node A will keep quite
A
B
C
61
Collision Avoidance

CSMA/CA: Wireless MAC protocols often use
collision avoidance techniques, in conjunction with a
(physical or virtual) carrier sense mechanism

Carrier sense: When a node wishes to transmit a
packet, it first waits until the channel is idle.

Collision avoidance: Nodes hearing RTS/CTS stay
silent for specified duration. Once channel becomes
idle, the node waits for a randomly chosen duration
before attempting to transmit.
62
IEEE 802.11
RTS = Request-to-Send
RTS
A
B
C
D
E
F
Pretending a circular range
63
IEEE 802.11
RTS = Request-to-Send
RTS
A
B
C
D
E
F
NAV = 10
64
NAV = remaining duration to keep quiet
IEEE 802.11
CTS = Clear-to-Send
CTS
A
B
C
D
E
F
65
IEEE 802.11
CTS = Clear-to-Send
CTS
A
B
C
D
E
F
NAV = 8
66
IEEE 802.11
•DATA packet follows CTS. Successful data reception
acknowledged using ACK.
DATA
A
B
C
D
E
F
67
IEEE 802.11
ACK
A
B
C
D
E
F
68
IEEE 802.11
Reserved area
(not necessarily
circular in
practice)
ACK
A
B
C
D
E
F
69
Backoff Interval

Backoff intervals used to reduce collision probability

When transmitting a packet, choose a backoff interval
in the range [0,cw]
cw is contention window

Count down the backoff interval when medium is idle
Count-down is suspended if medium becomes busy

When backoff interval reaches 0, transmit RTS
70
IEEE 802.11 DCF Example
B1 = 25
B1 = 5
wait
data
data
B2 = 20
cw = 31
wait
B2 = 15
B2 = 10
B1 and B2 are backoff intervals
at nodes 1 and 2
71
Backoff Interval

The time spent counting down backoff intervals is a
part of MAC overhead

Choosing a large cw leads to large backoff intervals
and can result in larger overhead

Choosing a small cw leads to a larger number of
collisions (when two nodes count down to 0
simultaneously)
72

Since the number of nodes attempting to transmit
simultaneously may change with time, some
mechanism to manage contention is needed

IEEE 802.11 DCF: contention window cw is chosen
dynamically depending on collision occurrence
73
Binary Exponential Backoff in DCF

When a node fails to receive CTS in response to its
RTS, it increases the contention window
cw is doubled (up to an upper bound)

When a node successfully completes a data transfer,
it restores cw to Cwmin

cw follows a sawtooth curve
74
Security and Misbehavior
75
Issues

Hosts may be misbehave or try to compromise
security at all layers of the protocol stack
76
Transport Layer
(End-to-End Communication)

How to secure end-to-end communication?

Need to know keys to be used for secure
communication

May want to anonymize the communication
77
Network Layer
Misbehaving hosts may create many hazards

May disrupt route discovery and maintenance:
Force use of poor routes (e.g., long routes)

Delay, drop, corrupt, misroute packets

May degrade performance by making good routes
look bad
78
MAC Layer

Disobey protocol specifications for selfish gains

Denial-of-service attacks
79
Scope of this Tutorial

Overview of selected issues at various protocol
layers

Not an exhaustive survey of all relevant problems or
solutions
80
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
81
Key Management
82
Key Management

In “pure” ad hoc networks, access to infrastructure
cannot be assumed

Network may also become partitioned

In “hybrid” networks, however, if access to
infrastructure is typically available, traditional
solutions can be extended with relative ease
83
Certification Authority

Certification Authority (CA) has a public/private key
pair, with public key known to all

CA signs certificate binding public keys to other
nodes

A single CA may not be enough – unavailability of the
CA (due to partitioning, failure or compromise) will
make it difficult for nodes to obtain public keys of
other hosts

A compromised CA may sign erroneous certificates
84
Distributed Certification Authority [Zhou99]

Use threshold cryptography to implement CA
functionality jointly at n nodes. The n CA servers
collectively have a public/private key pair
Each CA only knows a part of the private key
Can tolerate t compromised servers

Threshold cryptography: (n,t+1) threshold
cryptography scheme allows n parties to share the
ability to perform a cryptographic operation (e.g.,
creating a digital signature)
Any (t+1) parties can perform the operation jointly
No t or fewer parties can perform the operation
85
Distributed Certification Authority [Zhou99]

Each server knows public key of other servers, so
that the servers can communicate with each other
securely

To sign a certificate, each server generates a partial
signature for the certificate, and submits to a
combiner

To protect against a compromised combiner, use t+1
combiners
86
Self-Organized Public Key Management
[Capkun03]

Does not rely on availability of CA

Nodes form a “Certificate Graph”
each vertex represents a public key
an edge from Ku to Kw exists if there is a certificate signed by
the private key of node u that binds Kw to the identity of
some node w.
Ku
(w,Kw)Pr Ku
Kw
87
Self-Organized Public Key Management
[Capkun03]

Four steps of the management scheme

Step 1: Each node creates its own private/public keys.
Each node acts independently
88
Self-Organized Public Key Management

Step 2: When a node u believes that key Kw belongs to
node w, node u issues a public-key certificate in which
Kw is bound to w by the signature of u
u may believe this because u and w may have talked on a
dedicated channel previously
Each node also issues a self-signed certificate for its own key

Step 3: Nodes periodically exchange certificates with
other nodes they encounter
Mobility allows faster dissemination of certificates through the
network
89
Self-Organized Public Key Management

Step 4: Each node forms a certificate graph using the
certificates known to that node
Authentication: When a node u wants to verify the
authenticity of the public key Kv of node v, u tries to
find a directed graph from Ku to Kv in the certificate
graph. If such a path is found, the key is authentic.
90
Self-Organized Public Key Management

Misbehaving hosts may issue incorrect certificates

If there are mismatching certificates, indicates
presence of a misbehaving host (unless one of the
mismatching certificate has expired)
Mismatching certificates may bind same public key for two
different nodes, or same node to two different keys

To resolve the mismatch, a “confidence” level may be
calculated for each certificate chain that verifies each
of the mismatching certificates
Choose the certificate that can be verified with high
confidence – else ignore both certificates
91
TESLA Broadcast Authentication [Perrig]


How to verify authenticity of broadcast packets?
Use Message Authentication Code (MAC) for each
message, using a shared secret key
But with broadcast, all receivers need to know the shared
key, and any of them can then impersonate the sender

Use digital signature with asymmetric cryptography
Computationally expensive

Use asymmetric cryptography to bootstrap symmetric
cryptography solution  TESLA
92
TESLA

Uses one-way hash chains: Starting with initial value
s0, use one-way function F to general a sequence of
values s1 = F(s0), s2 = F(s1), … , sn = F(sn-1).

Knowing an earlier value in the chain, a latter value
can be determined, but not vice-versa

Use the values in reverse order, starting from sn-1
 Order of use opposite the order of generation

Distribute sn to all nodes with verifiable authenticity
Use digital signature (this is the “bootstrap” step)
Nodes need to know the source’s public key
93
TESLA

Messages sent during period i include Message
Authentication Code (MAC) computed using another
one-way function of si

The key si is revealed after a key disclosure delay of
d intervals

On receiving a message in interval i, a node X waits
for d-1 additional intervals for the key to be revealed)

When si is revealed, node X can verify that si+1 = F(si)
to determine authenticity of si
94
TESLA

Authenticity of si can be determined so long as node X
knows some sk with k>i
Allows for loss of revealed keys during broadcast operation

Once a key is revealed, anyone can try to impersonate
the sender using that key

To avoid this, TESLA assumes loose time
synchronization
Each receiver can place an upper bound on the sender’s clock
The error needs to be small compared to key disclosure delay
95
TESLA

If impersonator I receives key si from source S first,
and sends a packet to R impersonating S, R will find
the packet valid only if
The packet timestamp is smaller than the upper bound R
places on the time at S, and
Now, the upper bound when S sends key si will be at least i+d
(since the key is not released until interval i+d)
So if R only accepts packets sent with timestamp i but
received when the upper bound on S’s clock < i+d, there is no
way an impersonator can pass above conditions (provided
clock error small compared to d)
I
S
R
96
TESLA

Advantage: Use of asymmetric cryptography required
only initially (to distribute initial key using signatures)
Further communication uses MAC

Disadvantage: Messages can only be authenticated
after delay d
97
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
98
Secure Communication
99
Secure Communication

With the previously discussed mechanisms for key
distribution, it is possible to authenticate the
assignment of a public key to a node

This key can then be used for secure communication
The public key can be used to set up a symmetric key
between a given node pair as well
TESLA provides a mechanism for broadcast authentication
when a single source must broadcast packets to multiple
receivers
100
Secure Communication

Sometimes security requirement may include
anonymity

Availability of an authentic key is not enough to
prevent traffic analysis

We may want to hide the source or the destination of
a packet, or simply the amount of traffic between a
given pair of nodes
101
Traffic Analysis

Traditional approaches for anonymous
communication, for instance, based on MIX nodes or
dummy traffic insertion, can be used in wireless ad
hoc networks as well

However, it is possible to develop new approaches
considering the broadcast nature of the wireless
channel
102
Mix Nodes [Chaum]

Mix nodes can reorder packets from different flows,
insert dummy packets, or delay packets, to reduce
correlation between packets in and packets out
G
D
C
M1
B
M3
M2
E
F
A
103
Mix Nodes

Node A wants to send message M to node G. Node A
chooses 2 Mix nodes (in general n mix nodes), say,
M1 and M2
G
D
C
M1
B
M3
M2
E
F
A
104
Mix Nodes

Node A transmits to M1
message K1(R1, K2(R2, M))
where Ki() denotes encryption using public key Ki of
Mix i, and Ri is a random number
G
D
C
M1
B
M3
M2
E
F
A
105
Mix Nodes

M1 recovers K2(R2,M) and send to M2
G
D
C
M1
B
M3
M2
E
F
A
106
Mix Nodes

M2 recovers M and sends to G
G
D
C
M1
B
M3
M2
E
F
A
107
Mix Nodes

If M is encrypted by a secret key, no one other than G
or A can know M

Since M1 and M2 “mix” traffic, observers cannot
determine the source-destination pair without
compromising M1 and M2 both
108
Alternative Mix Nodes

Suppose A uses M2 and M3
 Need to take fewer hops
(not M1 and M2)

Choice of mix nodes affects overhead
G
D
C
M1
B
M3
M2
E
F
A
109
Mix Node Selection

Intelligent selection of mix nodes can reduce
overhead [Jiang04]

With mobility, the choice of mix nodes may have to
be modified to reduce cost

However, change of mix selection has the potential
for divulging more information
110
Traffic Mode Detection

Consider a node pair A and D. Depending on the
“mode” of operation, the traffic rate from A to D is
either R1 or R2.

To avoid detection of the mode, node A may always
send at rate max (R1, R2) inserting dummy traffic if
necessary [Venkatraman93]

This is an end-to-end approach, since it can be
implemented entirely at source & destination of a flow
111
Traffic Mode Detection




Now consider two flow A-D and E-F
Mode 1: A-D rate R1 E-F rate R2
Mode 2: A-D rate R2 E-F rate R1
End-to-end cover: A-D and E-F both at rate max (R1,R2)
Link BC carries traffic 2*max (R1,R2)
F
Max(R1,R2)
A
B
C
D
E
Max(R1,R2)
2 * Max(R1,R2)
112
Traffic Mode Detection

If we can encrypt link layer traffic in ad hoc networks,
then a “link” cover mode can be used, such that each link
carries fixed traffic independent of traffic mode

Reduces resource usage
F
A
B
E
C
D
Max(R1,R2) on each link except BC
R1+ R2 on link BC
113
Traffic Mode Detection

Insertion of dummy traffic on a per-link basis “cheaper”
than end-to-end [Radosavljevic92,Jiang01]

But need to take into account rates of different flows to
determine suitable level of padding

Also, need link layer encryption to disallow
differentiation of different flows at the link layer
114
Traffic Mode Detection

Mode 1: A-D rate R1
Mode 2: A-D rate R2
E-F rate R2
E-F rate R1

Need Max(R1,R2) on all links, since the two flows do
not share links

Node B transmits 2 * Max(R1,R2) traffic
F
A
B
E
D
115
Traffic Mode Detection

Node-level dummy packet insertion cheaper, if we can
hide link-level receiver of the packets

Without the dummy traffic, node B forwards traffic
R1+R2 independent of the mode

Node-level insertion: Maintain rates Max(R1,R2) at
nodes A and E, and rate R1+R2 at node B
F
A
B
E
D
116
Traffic Mode Detection

Node B needs to be able to remove dummy packets

Recipient of traffic from node B needs to be hidden
 Additional mechanisms can be designed for this
[Jiang05]
117
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
118
Misbehavior at the MAC Layer
119
MAC Layer Misbehavior
Access Point
Access Point
Wireless
channel
Wireless
channel
A
C
D
B

Nodes are required to follow
Medium Access Control
(MAC) rules

Misbehaving nodes may
violate MAC rules
120
Example

We will illustrate MAC layer misbehavior with
example misbehaviors that can occur with IEEE
802.11 DCF protocol

For ease of discussion, we sometimes refer to nodes
communicating with an “access point”, but the
discussion applies equally to nodes transmitting to
any node in an ad hoc network acting as their
receiver
121
Some Possible Misbehaviors

Causing collisions with other hosts’ RTS or CTS
[Raya]

Those hosts will exponentially backoff on packet loss,
giving free channel to the misbehaving host
122
Possible Misbehaviors:
“Impatient” Transmitters

Smaller backoff intervals [Kyasanur]

Shorter Interframe Spacings [Raya]
123
“Impatient” Transmitters

Backoff from biased distribution
Example: Always select a small backoff value
B1 = 1
B1 = 1
Misbehaving
node
Transmit
Transmit
Well-behaved
node
wait
wait
B2 = 20
B2 = 19
124
Impatient Transmitters

We will discuss the case of hosts that choose “too
small” backoff intervals

But other cases of hosts waiting too little before
talking can be handled analogously
125
Goals [Kyasanur03]

Diagnose node misbehavior
 Catch misbehaving nodes

Discourage misbehavior
 Punish misbehaving nodes
126
Potential Approaches

Watch idle times on the channel to detect when hosts
wait too little

Design protocols that improve the ability to detect
misbehavior

Protocols that discourage misbehavior [Konorski]
• Certain game-theoretic approaches
127
Passive Observation [Kyasanur03]
(Conceptually Simplest Solution)

802.11 dictates that each host must be idle for a
certain duration between transmissions

The duration can be expressed as
(K + v) where K is a constant, and v is chosen
probabilistically from a certain distribution

K due to inter-frame spacing

v due to randomly chosen backoff intervals
128
Passive Observation

The observer can measure the idle time on the
channel and determine whether the idle time is drawn
from the above distribution

If the observed idle time is smaller than expected,
then misbehavior can be detected [Kyasanur03]
[Cagalj05] presents an implementation based on this
approach
129
Passive Observation

With this approach, a receiver can try to diagnose
behavior of nodes trying to send packets to the receiver
Access Point
A
Wireless
channel
130
Issues

Wireless channel introduces uncertainties

Not all hosts see channel idle at the same time
AP1 sees channel busy, but A sees it as idle
AP 2
AP 1
A
Wireless
channel
B
Wireless
channel
131
Issues

Spatial channel variations bound the efficacy of
misbehavior detection mechanisms

Many existing proposals ignore channel variation when
performing evaluations, making the evaluations less
reliable
132
Issues

Receiver does not know exact backoff value
chosen by sender
 Sender chooses random backoff
 Hard to distinguish between maliciously chosen small values
and a legitimate value
133
Potential Solution:
Use long-term statistics [Kyasanur]

Observe backoffs chosen by sender over multiple
packets

Selecting right observation interval difficult
134
An Alternative Approach

Remove the non-determinism
135
An Alternative Approach

Receiver provides backoff values to sender
Receiver specifies backoff for next packet in ACK for current
packet

Modification does not significantly change 802.11
behavior
Backoffs of different nodes still independent
Uncertainty of sender’s backoff eliminated
136
Modifications to 802.11
B
Sender
S
Receiver
R
• R provides backoff B to S in ACK
B selected from [0,CWmin]
• S uses B for backoff
137
Protocol steps
Step 1: For each transmission:
 Detect deviations: Decide if sender backed off for less than

required number of slots
Penalize deviations: Penalty is added, if the sender appears to
have deviated
Goal: Identify and penalize suspected misbehavior
 Reacting to individual transmission makes it harder for the
cheater to adapt to the protocol
138
Protocol steps
Step 2: Based on last W transmissions:
 Diagnose misbehavior: Identify misbehaving nodes
Goal: Identify misbehaving nodes with high probability
 Reduce impact of channel uncertainties
 Filter out misbehaving nodes from well-behaved nodes
139
Detecting deviations
Backoff
Sender S
Receiver R
Bobsr

Receiver counts number of idle slots Bobsr
Condition for detecting deviations: Bobsr <  B
(0 <  <= 1)
140
Penalizing Misbehavior
Actual backoff < B
Sender
S
Receiver
R
Bobsr
When Bobsr <  B, penalty P added

P proportional to  B– Bobsr
Total backoff assigned = B + P
141
Penalty Scheme issues

Misbehaving sender has two options
Ignore assigned penalty  Easier to detect
Follow assigned penalty  No throughput gain

With penalty, sender has to misbehave more for same
throughput gain
142
Diagnosing Misbehavior

Total deviation for last W packets used
Deviation per packet is B – Bobsr

If total deviation > THRESH then sender is designated as
misbehaving

Higher layers / administrator can be informed of
misbehavior
143
Summary of Performance Results

Persistent misbehavior detected with high accuracy

Accuracy depends on channel conditions

Accuracy not 100% due to channel variations
• Accuracy increases with misbehavior
144
Variations – Multiple Observers

In an ad hoc networks, a node can only diagnose, on
its own, misbehavior by senders in its vicinity

Potential for error due to channel variations

Different hosts can cooperate to improve accuracy

Open problem: How to cooperate? How to “merge”
information to arrive at a diagnosis?
145
Other Approaches

Game theory

Incentive-based mechanisms
146
MAC Selfishness: Game-Theoretic Approach

[MacKenzie] addresses selfish misbehavior in Aloha
networks
Nodes can choose arbitrary access probabilities
Assign cost c for a transmission attempt
• Utility of a successful transmission = 1-c
• Utility of an unsuccessful transmission = -c
• Utility of no attempt = 0

MacKenzie’s contribution is to show that there exists a
Nash equilibrium strategy
147
MAC: Selfishness

Others have also attempted game-theoretic solutions
[Konorski,Cagalj05]

Limitation: Game-theoretic solutions (so far) assume
that all hosts see identical channel state
Not realistic
Limits usefulness of solutions
148
Incentive-Based Mechanisms [Zhong02]

Use payment schemes, charging per packet

Misbehaving hosts can get more throughput, but at a
higher cost
• This solution does not ensure fairness
• Also, misbehaving node can achieve lower delay at no extra
cost
• This suggests that per-packet payment is not enough
• Need to factor delay as well (harder)
149
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
150
Network Layer Misbehavior
151
Network Layer Misbehavior

Many potential misbehaviors have been identified in
various papers

We will discuss selected misbehaviors, and plausible
solutions
152
Drop/Corrupt/Misroute

A node “agrees” to join a route
(for instance, by forwarding route request in DSR)
but fails to forward packets correctly

A node may do so to conserve energy, or to launch a
denial-of-service attack, due to failure of some sort,
or because of overload
153
Watchdog Approach [Marti]

Verify whether a node has forwarded a packet or not
B sends packet to C
A
B
C
D
E
154
Watchdog Approach [Marti]



Verify whether a node has forwarded a packet or not
B can learn whether C has forwarded packet or not
B can also know whether packet is tampered with if no
per-link encryption
C forwards packet to D
A
B
C
D
E
B overhears C
Forwarding the packet
155
Watchdog Approach:
Buffering & Failure Detection

Forwarding by C may not be immediate: B must
buffer packets for some time, and compare them with
overheard packets
• Buffered packet can be removed on a match

If packet stays in buffer at B too long, a “failure tally”
for node C is incremented

If the failure rate is above a threshold, C is
determined as misbehaving, and source node
informed
156
Impact of Collisions

If A transmits while C is forwarding to D, A will not know
 Failure tally at C is not reliable. Include a margin for
such errors (which may be exploited by misbehaving
hosts)
C forwards packet to D
A
B
C
D
E
157
Reliability of Reception Not Known

Even if B sees the transmission from C, it cannot
always tell whether D received the packet reliably
 Misbehaving C may reduce power such that B can
receive from C, but D does not (provided path loss to
D is higher)
C forwards packet to D
A
B
C
D
E
158
Channel Variations May Cause False Detection



A
If channel quality between B and C changes often, B
may not overhear packets forwarded by C
This will increase C’s failure tally at B
May cause false misbehavior accusation
B
C
D
E
159
Malicious Reporting

Host D may be a good node, but C may report that D
is misbehaving

Source cannot tell whether this report is accurate

If the destination sends acknowledgement to source
for the received packets, and if the forward-reverse
routes are disjoint, this misbehavior (by C) may be
caught
160
Collusion

A
If C forwards packets to D, but fails to report when D
does not forward packets, the source node cannot
determine who is misbehaving
B
C
D
E
Collusion hard to detect in many other schemes as well
161
Misdirection of Packets



A
C forwards packets, but to the wrong node!
With DSR, B knows the next hop after C, so this
misbehavior may be detected
With other hop-by-hop forwarding protocols, B cannot
detect this
B
C
D
E
F
162
Directional Transmissions


A
Directional transmissions make it difficult to use
Watchdog
Power control for improved capacity or energy
efficiency can create difficulties as well
B
C
D
E
B cannot hear
C’s transmission to D
163
Watchdog + Pathrater [Marti]

“Pathrater” is run by each node. Each node assigns a
rating to each known node
Previously unknown nodes assigned “neutral” rating of 0.5
Rating assigned to nodes suspected of misbehaving are set
to large negative value
Other nodes have positive ratings (between 0 and 0.8)

Ratings of well-behaved nodes increase over time up
to a maximum
So a temporary misbehavior can be overcome by sustained
good behavior

Routes with larger cumulative node ratings preferred
164
Watchdog: Summary

Can detect misbehaving hosts, although not always;
false detection possible as well

Misbehaving hosts not punished
Effectively rewarded, by not sending any more traffic
through them
Potential modification: Punishment could be to not forward
any traffic from the misbehaving hosts
165
Hosts Bearing Grudges:
CONFIDANT Protocol [Buchegger]

Motivated by “The Selfish Gene” by Dawkins (1976)

Consider three types of birds
“Suckers” – Birds that always groom parasites off other
birds’ heads
“Cheats” – Birds that never help other birds
“Grudgers” – Birds that do not help known cheaters

If bird population starts out with only suckers and
cheats, both categories become extinct over time

If bird population contains grudgers, eventually they
dominate the population, and others become extinct
166
Hosts Bearing Grudges

Applying the “grudgers” concept to ad hoc networks

Each node determines whether its neighbor is
misbehaving
• Similar to the previous scheme

A node ALARMs its “friends” when a misbehaving
hosts is detected

Each node maintains reputation ratings for other
nodes that are reduced on receipt of ALARMs

Ratings improve with time – a cheater can
rehabilitate itself
167
Hosts Bearing Grudges: Issues

How to decide on friends?

What if “friends” cheat?
168
Hosts Bearing Grudges: Summary

Reputation-based scheme

Nodes prefer to route through & for nodes with higher
reputation

Interesting concept, but cannot circumvent the
difficulties in diagnosing misbehavior accurately
169
Exploiting Path Redundancy [Xue04]

Design routing algorithms that can deliver data
despite misbehaving nodes

“Tolerate” misbehavior by using disjoint routes

Prefer routes that deliver packets at a higher “delivery
ratio”
170
Exploiting Path Redundancy

Alternate routes: AFGE, ABCDE, ABFGE, ABCGE
E
F
A
B
G
C
D
171
Exploiting Path Redundancy


Misbehaving host F drops packets
Delivery ratio poor on routes AFGE, ABFGE,
better on ABCDE, ABCGE
E
F
A
B
G
C
D
172
Best-Effort Fault Tolerant Routing (BFTR)
– Modified DSR [Xue04]

The target of a route discovery is required to send
multiple route replies (RREP)
 The source can discover multiple routes
(all are deemed feasible initially)
(1) The source chooses a feasible route based on the
“shortest path” metric
(2) The source uses this route until its delivery ratio falls
below a threshold (making the route infeasible)
(3) If existing route is deemed infeasible, go to (1)
173
BFTR: Issues

A route may look infeasible due to temporary
overload on that route

The source may settle on a poorer (but feasible)
route

No direct mechanism to differentiate misbehavior
from lower capacity routes
This is both an advantage, and a potential shortcoming
174
Information Dispersal [Rabin89]

Map the N bit information F to n pieces, each N/m in
size, such that any m pieces suffice to reconstruct
original information
• Total size = n/m * N

Divide information F into N/m sequences of length m
S1 = (b1, …, bm)
S2 = (bm+1, …, b2m)
…
175
Information Dispersal

Choose n vectors ai = (ai1, …, aim)
Such that any set of m different vectors are
linearly independent

Let Fi = (ci1, ci2, …, ciN/m)
1<= i <= n
where cik = ai . Sk
Example: ci1 = ai.b1 + ai2.b2 + … + aim . bm
176
Information Dispersal [Rabin89]

Given m pieces, say, F1, …, Fm, we can reconstruct F
as follows

Let A = (aij) 1<=i,j<= m
 A . Sk’ = (c11, c21, …, cm1)’
’ denotes transpose
Thus, knowing A and Fi= (ci1, ci2, …, ciN/m),
we can recover S
177
Information Dispersal to Tolerate Misbehavior
[Papadimitratos03]

Choose n node-disjoint paths to send the n pieces of
information

Use a route rating scheme (based on delivery ratios) to
select the routes

Acknowledgements for received pieces are sent

The missing pieces retransmitted on other routes

Need to be able to detect whether packets are
tampered with
178
Route Tampering Attack

A node may make a route appear too long or
too short by tampering with RREQ in DSR

By making a route appear too long, the node may
avoid the route from being used
This would happen if the destination replies to multiple
RREQ in DSR

By making a route appear too short, the node may
make the source use that route, and then drop data
packets (denial of service)
179
Node Insertion
Y
Z
[S,E]
S
E
F
B
[S,E,P,Q,F]
C
M
J
A
L
G
H
K
I
D
N
180
Node Deletion
Y
Z
S
E
F
B
C
M
J
A
L
G
H
I
[S,C,G]
D
K
[S,G,K]
N
181
Route Tampering Attack

Useful to allow detection of route tampering

Solution:
Protect route accumulated in RREQ from tampering
Removal or insertion of nodes should both be detected
182
Ariadne [Hu]: Detecting Route Tampering

Source-Destination S-D pairs share secret keys Ksd
and Kds for each direction of communication

One-way hash function H available

MAC = Message Authentication Code (MAC)
computed using MAC keys
183
Ariadne [Hu]: Detecting Route Tampering

Let RREQ’ denote the RREQ that would have been
sent in unmodified DSR

Source S broadcasts RREQ = RREQ’,h0,[]
where h0 = HMACKsd(RREQ’)

When a node X receives an
RREQ = (RREQ’, hi, [m list])
it broadcasts RREQ, mi+1
where RREQ = (RREQ’, hi+1, [m list]), mi+1
where hi+1 = H(X, hi) and mi+1=HMACKx(RREQ)
184
Ariadne

If D receives an RREQ that came via route S, A, B, C, then D
should have received
h = H(C, H(B, H(A, HMACKsd(initial RREQ’))))

Knowing H and Ksd, and the node identifiers appended in the
RREQ, D can verify accuracy of received h
 Relies on the inability to invert function H
 A mismatch indicates tampering with h or node list
 A match indicates that the h value corresponds to the node-list
Not enough to know whether the node-list is accurate

If no tampering detected in h, send RREP including node-list and
m-list, and HMAC for this information
185
Ariadne

Node D sends the RREP to node C (first node on reverse route)

Node C forwards to the next node towards the source, but also
appends its key Kc to the message
One key used per route discovery (TESLA mechanism).
S can verify authenticity of this key
Alternate mechanisms: Use pair-wise shared secret keys, or
signatures using authentic public keys

Node S receives all the keys, and also the m-list in RREP

S can verify that all m values in the m-list are accurate, in addition
to the HMAC computed by D

If all check out, then no tampering, else discard RREP
186
Ariadne

If HMAC checks, then no one tampered with the
node-list and m-list in the RREP

If m-list checks, then the m values were computed by
legitimate nodes when RREQ forwarded

If all OK, accept RREP

Use of m-list ensures that a host cannot tamper with
the RREP
 Route in RREP is the route taken by RREQ and
RREP
187
Ariadne: Issues

Ensuring that RREQ and RREP follow the known
route does not ensure that the nodes on the route will
deliver packets correctly

So this is not a sufficient solution
(and some might argue, not necessary!)
188
Wormhole Attack [Hu]

In this attack, the attacker makes a wireless “link”
appear in the network when there isn’t one

The attacker may achieve this by using an out-ofband channel, or a channel that cannot be detected
by other hosts

Not necessarily detrimental, since the additional link
can improve performance

But the attacker may cause the network to funnel
traffic through this link, giving the attacker control on
the fate of the traffic
189
Wormhole Attack [Hu]


Host X can forward packets from F and E unaltered
Hosts F and E will seem “adjacent” to each other
E
F
A
B
X
C
D
190
Wormhole Attack [Hu]



With DSR, RREQ via AFXE will likely arrive at E
soonest
The RREQ will contain route AFE
When RREP from E reaches A, it will start using AFE
The fact that AFE really is AFXE will not be detected
E
F
A
B
X
C
D
191
Wormhole Attack [Hu]



With DSR, RREQ via AFXE will likely arrive at E
soonest
The RREQ will contain route AFE
When RREP from E reaches A, it will start using AFE
The fact that AFE really is AFXE will not be detected
E
F
A
B
X
C
D
192
Wormhole Attack [Hu]

Subsequently when A sends data along AFE, node X
will not forward the data to E
E
F
A
B
X
C
D
193
Wormhole Attack: Issues


Not that simple to launch an undetected wormhole
attack
If node F can “see” someone else sending packets
with F specified as sender, the attack is detected
 Transmissions from X must be invisible to F
E
F
A
B
X
C
D
194
Wormhole Attack: Issues



Transmissions from X must be invisible to F
Use directional transmissions at X to forward packets
Difficult for X to guarantee that F will not see its
transmissions (depends on beamforms, multipath)
E
F
A
B
X
C
D
195
Wormhole Attack: Issues



Transmissions from X must be invisible to F
Out-of-band collusion between two attackers X and Y
Difficult for Y to guarantee that F will not see its
transmissions
Y
E
F
A
B
X
C
D
196
Wormhole Attack: Issues



Timing: F may expect an “immediate ACK”
In the absence of authentication, X can ACK packets
to F without having delivered them to E
With authentication, this is difficult
E
F
A
B
X
C
D
197
Timing Issue


Alternatively, the attacker must be able to forward
bits as soon as it starts receiving them from F
X transmits to E while receiving from F on the same channel
If no delays introduced, E and F may not detect the
attack
E
F
A
B
X
C
D
198
Detected Attack
If timing issue cannot be resolved by the attacker ….

If X cannot deliver a timely ACK, the link E  F will
appear broken to E (because no ACK when expected)

Thus, even though E appears to receive RREQ from F,
it cannot deliver packets to F

The attack will make the link F-E seem unidirectional
(unreliable broadcast from F to E works, but not
reliable unicast from E to F).
 Mechanisms to handle unidirectional links (“blacklist”)
199
can potentially suffice
Other Detection Mechanisms:
Geographical Leashes

Geographical Leashes: Each transmission from a
host should be allowed to propagate over a limited
distance

If E and F are too far, F should reject packets that
seem to be transmitted by E, even if received reliably

Need an estimate of distance between E and F (GPS
locations + mobility during packet transmission)
200
Geographical Leashes [Hu]

Difficulty: Packets may travel along non line-of-sight
paths
Hard to predict the actual “distance” traveled by the
transmissions

Difficulty: A related problem is that physically close
hosts may not be able to communicate directly
(because of obstacles)
The attacker may still introduce a tunnel (wormhole)
between these hosts
However, the attacker needs the information that the two
hosts cannot see each other – difficult to get this information
201
Temporal Leashes

Assume tight clock synchronization (e.g., GPS)

Sender timestamps the packet, and receiver
determines the delay since the packet was sent

If delay too large, reject the packet

The timestamps must be protected by some
authentication mechanism or signature
202
Wormhole Attack: Summary

Not clear that this attack is easy to launch undetected
• The attacker needs knowledge of propagation to be sure
of avoiding detection

Solutions dealing with unidirectional links may suffice
in some cases
203
Outline







Introduction to ad hoc networks
Selected routing and MAC protocols
Key management in wireless ad hoc networks
Secure communication in ad hoc networks
Misbehavior at the MAC layer
Misbehavior at the network layer
Anomaly detection
204
Anomaly Detection
205
Anomaly Detection

Anomaly detection: Detect deviation from “normal”
behavior
Need to characterize “normal”
Normal behavior hard to characterize accurately
Need to be able to determine when observed behavior
departs significantly from the norm
Avoid false positives

The MAC layer approach for detecting deviation from
“normal” distribution of contention window
parameters can be considered an “anomaly
detection” scheme
206
Anomaly Detection in Ad Hoc Networks
[Zhang00]

Anomaly detection may also be useful at other layers,
particularly, network layer

How to characterize “normal” routing protocol
behavior?

Some of the routing mechanisms we discussed
earlier do detect specific forms of abnormal behavior,
but a more generic approach is desired

Can we design a protocol-independent anomaly
detection mechanism? Not clear
207
Anomaly Detection

We limit our discussion here

Wireless harder than wired networks due to spatial
and temporal variations
208
Conclusions
209
Conclusion

Security an important consideration for widespread
deployment of wireless ad hoc networks

We discussed a sampling of topics in security and
misbehavior in ad hoc networks

Some issues are similar to those in wired networks

The differences from wired network arise due to
Shared nature of the wireless channel with variations over
space/time
Inability to rely on access to “infrastructure”
Ease of intrusion (relative to wired networks)
210
Conclusion

A lot of interesting research ongoing

One concern is that not all attacks are equally likely
Attackers will typically go after the weakest feature

Nevertheless an important area of research with
potential for future applications
211
Some Relevant Conferences/Workshops

ACM Wireless Security Workshop (WiSe) – held at
ACM MobiCom last few years

Traditional security conferences (Security and
Privacy, DSN, etc.)

Networking conferences: ACM MobiCom, ACM
MobiHoc, IEEE INFOCOM, etc.
212
Thanks!
www.crhc.uiuc.edu/wireless
nhv@uiuc.edu
213
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