Slides-ICISS.ppt

Security Issues and Challenges in
Wireless Networks
Kishore Kothapalli
Bruhadeshwar Bezawada
Center for Security, Theory, and Algorithmic Research
(CSTAR)
International Institute of Information Technology
Hyderabad, INDIA

Introduction
 Wireless stations, or nodes, communicate over a wireless medium
 Networks operating under infrastructure mode e.g., 802.11, 802.16,
Cellular networks
 Networks operating with limited or no infrastructural support e.g., ad
hoc networks in AODV mode
 Security threats are imminent due to the open nature of
communication
 Two main issues: authentication and privacy
 Other serious issues: denial-of-service
 A categorization is required to understand the issues in each
situation.

Introduction – Wireless Technologies
 Different technologies have been developed for
different scenarios and requirements
 WiFi is technology for Wireless LANs and short range
mobile access networks
 WiMAX is technology for last mile broadband
connectivity
 Wireless USB is technology for Internet connectivity
on the go
 Other technologies like Infrared (TV remotes etc),
Bluetooth (soon to be obsolete) etc are short range
 Extreme bandwidth but short range technologies are
Gigabit wireless etc

Introduction
 Fixed Infrastructure
 Base stations that are typically not resource constrained.
 Examples: sensor networks, and cellular networks.
 Mobility of nodes but not of base stations.

Introduction
 Ad hoc wireless networks
 No infrastructural support.
 Nodes also double up as routers.
 Mobility of nodes.
 Examples laptops/cellphones operating in ad hoc mode.
Image from
www.microsoft.com

Introduction
 Mixed mode
 In between the two modes.
 Some nodes exhibit ad hoc capability.

Introduction
 To formalize study and solutions, need good models
for these networks.
 Formal model to characterize the properties and
solutions
 Models that are close to reality
 Still allow for solution design and analysis.

Introduction
 Solution properties
 Light-weight
 Have to use battery power wisely.
 Other resources, such as storage, are also limited.
 Local control
 Many cases, only neighbours are known.
 Any additional information gathering is expensive.

Introduction
 Difficulty of modeling wireless networks as opposed to
wired networks:
 Transmission
 Interference
 Resource constraints
 Mobility
 Physical carrier sensing

Outline
 Introduction
 Models of Wireless Networks
 Various Layers and Current Solutions for each Layer
 Security Issues and Threats at each Layer
 Security Solutions
 Open Problems

Models of Wireless Networks
 Unit disk graph model
 Given a transmission radius R, nodes u,v are connected
if d(u,v) ≤ R
u
R
v
u'

 Unit disk graph model
 Given a transmission radius R, nodes u,v are connected
if d(u,v) ≤ R.
 Too simple model – transmission range could be of
arbitrary shape.
R
R
u
u
R
v
u'

 Packet Radio Network (PRN)
 Can handle arbitrary shapes
 Widely used
 Nodes u, v can communicate directly if they are
within each other's transmission range, rt.
u
v
w
v'

What is the problem?
 Model for interference too simplistic
u
v
w
v'

 w can still interfere at u
 PRN model fails to address certain interference
problems in practice
v
n – 2
s
t
≤ rt
≤ rt
≥ ri
≥ rt
What is the problem?
u
v
w
v'

 Transmission Range, Interference
Range
 Separate values for transmission
range, interference range.
 Interference range constant times
bigger than transmission range.
 Used in e.g., [Adler and
Scheideler '98], [Kuhn et. al., '04]
u
rt
v
w
u'
ri

 Transmission Range, Interference
Range
 Separate values for transmission
range, interference range.
 Interference range constant times
bigger than transmission range.
 Used in e.g., [Adler and
Scheideler '98], [Kuhn et. al., '04]
 What is the problem?
 Extension of unit disk model to
handle interference
u
rt
v
w
u'
ri

Model Based on Cost Function
 Gr = (V, Er), set of nodes V, Euclidean distance d(u, v)
 c is a cost function on nodes
 symmetric: c(u,v) = c(v,u)
  [0,1), depends on the environment
 c(u,v)  [(1 –  )•d(u, v), (1 + ) •d(u, v)]
w
u
v
a
b
Edge (u,v)  Er
if and only if
c(u,v) ≤ r

Transmission and Interference Range
 Transmission range rt(P), Interference range, ri(P)
 If c(v,w)  ri(P), node v can cause interference at node w.
 If c(v,w)  rt(P) then v is guaranteed to receive the message from w
provided no other node v' with c(v, v') ≤ ri(P) also transmits at the
same time.
w
rt(P)
v'
ri(P)
u
v c(v,w) rt(P)
c(v, v') ri(P)

Carrier Sensing
 Virtual carrier sensing using RTS/CTS.
 Physical Carrier Sensing
 Provided by Clear Channel Assessment (CCA) circuit.
 Monitor the medium as a function of Received Signal
Strength Indicator (RSSI)
 Energy Detection (ED) bit set to 1 if RSSI exceeds a
certain threshold
 Has a register to set the threshold in dB

Physical Carrier Sensing
 Carrier sense transmission (CST) range, rst(T, P)
 Carrier sense interference (CSI) range, rsi(T, P)
 Beyond the CSI range, sensing is not possible.
 Both the ranges grow monotonically in T and P.
w
v
rst(T,P)
v'
v''
rsi(T,P)
c(w,v) rst(T, P)
c(w, v') rsi(T, P)
c(w, v'') rsi(T, P)

Outline
 Introduction
 Models of Wireless Networks
 Various Layers and Current Solutions at each layer
 Security Issues and Threats at each Layer
 Security Solutions
 Open Problems

Various Layers of Interest – Physical Layer
 Physical Layer
 802.11 standard supports several data rates between
11 Mbps and 54 Mbps
 802.16 support multiple data rates from 2Mbps to 300
Mbps
 Several modulation schemes in use and support
different conditions and data rates
 AM, FM, PSK, BPSK, QPSK, FDM, OFDM, OFDMA, ...

Physical Layer – WiFi
 Stands for Wireless Fidelity Range of Technologies
 Technology that uses IEEE 802.11 protocol standards
 802.11b operates at 2.4 Ghz using DSSS
 Has three non-overlapping channels with 11mbps max
 802.11g operates at 2.4 Ghz resp, with 20 Mhz, OFDM
 Achieves 54 Mbps and inter-operable to 802.11b
 802.11a operates at 5GHz using OFDM
 About 4-8 (depending on country) non-overlapping
channels
 Bandwidth achieved is 54 Mbps

Various Layers of Interest – MAC Layer
 MAC Layer
 Medium access control is an important requirement.
 Collision detection (CSMA/CD) not possible unlike wired
networks.
 Hence using Collision avoidance (CSMA/CA)
 Functions of MAC
 Scanning, Authentication, Association, WEP, RTS/CTS,
Power Save options, Fragmentation

 802.11 MAC
 Use Physical Carrier Sensing to sense for a free
medium.
 Explicit ACKs to indicate reception of packet.
 Results in the problem of hidden node.
 Use Virtual Carrier Sensing using RTS/CTS.
DATA
DATA

 Virtual Carrier Sensing cannot solve the exposed node
problem.
 A and D cannot succeed simultaneously.
DATA
DATA
A
B
C
D

Other MAC Techniques
 Cell phone networks
 Node to base station and vice-versa.
 Fixed frequency for communication pair (FDD).
 Separate frequencies for each pair.
 Different technologies Analog/CDMA/GSM support
different number of simultaneous communications per
band.
 802.16 has a Receive/Grant model which is basically
TDD (Time-Division Duplexing)
 More efficient than FDD.

MAC Layer
 More recent solutions address issues such as,
especially with respect to ad hoc networks
 self-stabilization
 Dynamism
 Efficiency
 Fairness

Various Layers – Network Layer
 Route packets in the network.
 Routing in infrastructure based networks is similar to
IP routing
 All the base stations have a wired IP interface which is
used by the routers/switches to forward data
 Issues like handoffs are handled through techniques
like Mobile IP or Cellular Handoffs or Soft-handoffs as
done in Mobile WiMAX
 Now, for network without infrastructure the problem is
difficult as the routes are transient

Various Layers – Network Layer
 Ad hoc networks
 No easy solutions but different proposals exist.
 Two kinds: proactive and reactive
 Proactive: Maintain lot of state, proactive updates.
 Example: DSDV, DSR
 Reactive: Minimal state, react to changes.
 Example: AODV

Other Important Layers
 Transport layer
 This is important layer especially since the wireless
medium suffers from high bit-error rate and collisions.
 To offset this wireless technologies rely less on TCP’s
reliability mechanism
 This is mostly handled at physical layer through
techniques like FEC and other error correcting codes
 Application Layer
 Notion of an application layer protocol
 Email/Web/Games/SMS/MMS

Threats in Present Solutions – MAC Layer
 Denial of Service
 Can hog the medium by sending noise continuously.
 Can be done without draining the power of the
adversary.
 Depends on physical carrier sensing threshold.
z
A

Threats in Present Solutions – MAC Layer
 802.11 standard uses Access Control Lists for
admission control.
 If MAC address not in the list, then the node is denied
access.
 But easy to spoof MAC addresses.
00:1A:A0:FD:FF:2E
00:0C:76:7F:DF:49
00:13:D3:07:2F:A8
00:2F:B8:77:EA:B5

Threats in Present Solutions – Network Layer
 Ad hoc networks
 Network layer
 Denial-of-service attacks
 Broadcast nature of communication
 Packet dropping
 Route discovery failure in ad hoc network
 Packet rerouting

 Denial-of-service
 Easy to mount in wireless network protocols.
 One strategically adversary can generally disable a
dense part of the network.
z
A
Nodes Disrupting Routes
Source
Source
Destination

 Can simply engage in conversation and drain battery
power of other nodes – power exhaustion attack
 Send lot of RREQ messages but never use the routes.
z
A
RREQ(a)
RREQ(b)
RREQ(c)
….

 Broadcast nature of communication
 Each message can be received by all nodes in the
transmission range
 Packet sniffing is a lot easier than in wired networks.
 Poses a data privacy issue
s
t
A

 Route discovery in ad hoc networks
 AODV discovers route by RREQ/RREP.
 Few adversarial nodes can fail route discovery.
 Difficult to detect route discovery failures.
 Also vulnerable to RREP replays.
RREQ
RREQ

 Packet dropping
 Wired networks can monitor packet drops reasonably
 Such mechanisms are resource intensive for wireless
networks
 AODV has timeouts but no theoretical solutions
 Difficult to distinguish packet drops, say RREQs, from
non-existence of route itself
 Nodes some times behave selfishly to preserve
resources

 Packet rerouting – also known as data plane attacks.
 Attacker reveals paths but does not forward data along
these paths.
 Control plane measures do not suffice.
 Difficult to trace in wired networks also [Gouda, 2007].
s
t

 Application Layer
 Easy to infect mobile devices.
 Rerouting content through the base station poses
privacy issues.
 Bluetooth networks and ad hoc networks do not have a
base station facility.
 Contrast with wired networks with firewalls, filters,
sandboxes.

Security Solutions
 Requirements
 Need solutions that do not add any perceivable burden
 Cryptography can help
 Public key solutions
 Public key operations about 1000 times slow compared to symmetric key
operations.
 Cost of SHA-1 = 2 microseconds
 Cost of RSA signature verification = order of millisec
 Symmetric key solutions for privacy and authentication
 Issue: How to distribute and manage keys?

Security Solutions for 802.11 Networks
 Previous WEP (Wired Equivalent Privacy) based on
RC4 is prone to attacks
 Privacy is not guaranteed as the key streams could be
easily recovered
 Weaknesses in RC4 are well documented
 Authentication is weak as well due to weak encryption
technique
 Challenge-response using pre-shared keys is prone to
attacks if encryption is weak

Previous WEP Solution using RC4
 RC4 is a Vernam Cipher meaning primary operations are XOR with pseudo-random bytes
 Per-packet encryption key is 24-bit IV concatenated to a pre-shared key
 Integrity Check Vector (ICV) is CRC-32 over plain-text (used as Message Authentication Code)
 Data and ICV are encrypted using per-packet encryption key
 Problem
 RC4 is weak (as the IV is reused) and can allow an attacker to get the key stream used
 The ICV can enable one to check the validity of the key stream recovered
802.11 Hdr Data
802.11 Hdr Data
IV ICV
Encapsulate Decapsulate

WEP Authentication Model
WEP Authentication Based on RC4
 Authentication key is distributed out-of-band
 Access Point generates a randomly generated challenge
 Station encrypts challenge using pre-shared secret
 Problem: Challenge-responses of valid users can be recorded and key stream can
be recovered due to RC4 working
 Attacker can use the keys to encrypt any future challenges
Challenge (Nonce)
Response (Nonce RC4 encrypted under shared key)
Wireless
Node
AP
Shared secret distributed out of band
Decrypted nonce OK?

Security Solution for 802.11 Networks:
802.11i Model
 Solution Requirements
 Mutual authentication
 Scalable key management for large networks
 Central authorization and accounting
 Support for extended authentication like smart cards
 Key Management Issues
 Need to dynamically manage keys to avoid manual
reconfiguration difficulties especially for large networks

Current Standard: 802.11i or WPA2
 802.1X for Authentication Based on EAP (Extensible
Authentication Protocol)
 Port based authentication
 Access denied if port authentication fails
 CCMP (Counter Mode CBC-MAC Protocol) using AES
for confidentiality, integrity and origin authentication
 Dynamic Key Management

802.1X Key Management
 LEAP use dynamically generated WEP keys to secure authentication data
 EAP-TLS –Station and Access Point use public-key certificates through a
TLS tunnel
 Session key can be exchanged
 Mutual-authentication as both parties have digital certificates
 EAP-TTLS and PEAP –Only server-side certificate is needed
 Simplifies implementation where certificate management is difficult
 EAP-GSS where the authenticator is required to be in contact with a KDC

Key Derivation in 802.11i
 At the end of EAPOL: Station and Server share a Master Key: MK (E.g., Using EAP-
TLS)
 Both the Station and the AP derive a new key, called the Pairwise Master Key (PMK),
from the Master Key.
 Radius Server moves PMK to AP
 A 4−way handshake between the station and the AP to derive, bind, and verify a
Pairwise Transient Key (PTK).
 Key Confirmation Key (KCK), as the name implies, is used to prove the posession of
the PMK
 Key Encryption Key (KEK) is used to distributed the Group Transient Key (GTK)
 Temporal Key 1 & 2 (TK1/TK2) are used for encryption.
 The KEK is used to send the Group Transient Key (GTK) from AP to the station
 The GTK is a shared key among all stations connected to the same authenticator
(AP), to secure multicast/broadcast traffic

Security Solutions for 802.16 Networks
 802.16 or popularly WiMAX use X.509 certificates for authentication
 Subscriber Station authentication using X.509 certificate
 Establish security association (SAID)
 Authentication Key (AK) exchange
 AK is encrypted using public key of SS
 Authentication is completed when both SS and BS verify possession AK
 AK is used to exchange the TEK (Traffic encryption key)
 Base station generates TEK randomly and encrypts using KEK
generated from AK
 802.16 uses AES in CCM mode for privacy
 Mutual authentication is possible through EAP-TLS etc (802.16e)

Security in Ad Hoc Mode
 Ad hoc networks cannot use RADIUS type authentication
 Problem: if RADIUS type authentication is used, every station will need to
store every other station’s credentials
 Moreover, authentication will have to be using EAP-TLS which is
computationally intensive
 Problem: mutual authentication is trouble some
 Other Security Requirements
 Cryptographic mechanisms for confidentiality
 Key establishment for confidentiality
 Public-key management to prevent replacement of keys
 Symmetric key management to protect from compromise
 Denial-of-service resistance in contention mechanisms at MAC layer

Security in Ad Hoc Networks
 Security Mechanisms
 Pro-active : Prevents an attacker from launching an attack say by
using cryptographic mechanisms
 Requirement is establishment of necessary cryptographic material
 E.g., Routing Attacks
 Reactive : Relies on detection and mitigation of attacks
 Benign behaviour is defined and behaviour analysis is done to detect
malicious behaviour
 E.g., Packet Forwarding attacks

Key Management in Ad Hoc Networks- An
Overview
 Key management – Manage a set of secure communication
channels so that
 Use as few keys as possible
 Avoid centralized infrastructure during sessions
 Minimal cryptographic/message overhead
 Ensure “reasonable” security
 Two scenarios
 Broadcast security
 Peer-to-peer security

Security Solutions – Broadcast Security
 Base station and a set of nodes.
 Base station sends updates to all the nodes using broadcast.
 N = number of satellite nodes
 Authentication and privacy is required

Trivial Solution
 Each node shares a key with the base station.
 Storage is O(N) for sender and does not scale well
 Authentication is expensive especially if messages need to be
broadcast
K6
K8
K1
K7
K4
K2
K5
K3
K1, K2, K3, K4,
K5, K6, K7, K8

Broadcast Security
 Maintain a set O(log N)
 Each satellite node gets a subset of log n keys of S.
 Privacy: use XOR of keys to communicate with the user
 Authentication: sender adds MAC using all its keys
 Each node verifies signatures that can be generated using its subset of
keys
K1, K2, K3,
K4, K5
MACK1(M) MACK2(M) MACK5(M)
MACK4(M)
MACK3(M)
Message
K1, K3, K5
K1, K2, K4
K1, K3, K4
K2, K5, K4
K1, K2, K5
K1, K2, K3
K1, K5, K4
K2, K5, K3

Broadcast Security
 Collusion is an issue
 A larger pool of keys can be selected
 For N users O(log N) keys can give good results
 Scales well as the sender only needs to give a new subset of keys to a new user
K1, K3, K5
K1, K2, K4
K1, K3, K4
K2, K5, K4
K1, K2, K5
K1, K2, K3
K1, K5, K4
K2, K5, K3
K1, K2, K3
K4, K5, K6,
K7, K8

Security Solutions
 Privacy in a Peer-to-peer situation
 Public-key cryptography can be of use but expensive
 Key distribution is a major hurdle given that communicating parties are
not known in advance
 Anyone can communicate with any one
 Trivial Solution: one unique key per pair of users work
 Expensive
 Not scalable if new user gets added
 Revocation is little more tricky
 Scalable approach : key pre-distribution

Point-to-Point Security
 Point-to-Point security
 Need a key for every pair of nodes in an n node network.
 Trivial solution requires storing n – 1 keys at every node.
 Not scalable on the space usage.
A B
C
D
KAB
KAD
KAC
KBC
KCD
KBD
KCD
C-D
KBD
B-D
KBC
B-C
KAD
A-D
KAC
A-C
KAB
A-B

 Random Key Pre-distribution
A B
C
D
Pool of Keys
K1, K2, K3, K4, K5, K6,
K7, K8, K9, K10, K11,
K12, K13, K14, K15
K1, K2, K5, K6 K3, K9, K5, K11
K12, K11, K13, K15
K1, K15, K9, K13
K5
K11
K1+K15+K13
K1
E
F
G
K1, K5, K9, K13
G
K3, K5, K7, K9, K15
F
K10, K4, K5, K8, K7
E
K1, K15, K9, K13
D
K12, K11, K13, K15
C
K3, K9, K5, K11
B
K1, K2, K5, K6
A

 Issues in Random Key Pre-Distribution
 May need Intermediaries for key establishment
 Storage is High
 Experimental: 250 keys out of 10,000 keys may be necessary
 An active adversary is dangerous
 Collusion effect is unknown due to the randomness of key
distribution
 Might require privacy mechanisms to hide key sharing patterns
 Revocation issues exist
 Probabilistic arguments for size of key storage and connectivity
possible
 Practice proves otherwise, especially for sparse graphs

Some Solutions –Key Establishment
 Multi-path Key Establishment
A B
C
D
Pool of Keys
K1, K2, K3, K4, K5, K6,
K7, K8, K9, K10, K11,
K12, K13, K14, K15
K1, K2, K5, K6 K3, K9, K5, K11
K12, K11, K13, K15
K1, K15, K9, K13
K5
K11
K1+K15+K13
K1
E
F
G
K1, K5, K9, K13
G
K3, K5, K7, K9, K15
F
K10, K4, K5, K8, K7
E
K1, K15, K9, K13
D
K12, K11, K13, K15
C
K3, K9, K5, K11
B
K1, K2, K5, K6
A

 Deterministic Solution –Square Grid [Ref. 4]
[0,0] [0,1] [0,2] [0,3]
[1,0] [1,1] [1,2] [1,3]
[2,0]
[3,0]
[2,1] [2,2] [2,3]
[3,1] [3,2] [3,3]
User Placement

 Deterministic Solution –Square Grid
[0,0] [0,1] [0,2] [0,3]
[1,0] [1,2]
[2,0]
[3,0]
[2,2]
[3,2]
Kg(0,0)
Kg(2,2)
[2,3]
[2,1]
Grid Secrets

[0,0
]
[0,1] [0,2] [0,3]
[1,0]
[2,0]
[3,0]
Direct Secrets

[0,0] [0,1] [0,2] [0,3]
[1,0] [1,2]
[2,0]
[3,0]
[2,2]
[3,2]
[2,3]
[2,1]
Communication
Along Same
Row/Column

[0,0] [0,1] [0,2] [0,3]
[1,0] [1,2]
[2,0]
[3,0]
[2,2]
[3,2]
Kg(0,2)
Kg(2,0)
[2,3]
[2,1]
Communication
Among Users of
Different
Rows/Columns

 Square Grid Features and Issues
 Mobility has no effect on key establishment –always guaranteed by
design
 Failure tolerant –failure of links hardly matters
 Storage is high, but comparable to random KPS
 Collusion resistance is slightly weak
 Two users are sufficient to compromise session key
 Scalability is weak as the grid size is fixed before hand
 Optimizations possible, by choosing higher grid size and allowing for
some additional users

Security Solutions
 Can reduce storage further by considering a k – dimensional grid
 User belongs to multiple grids with lower dimension: n1/k
 number of keys stored per node decreases to kn1/k.
 At k = log n, this reduces to log n.
 But collusion resistance decreases with increasing k
 Best case storage is around: 12log2n
 Lower values are possible but multiplication constant is higher

Security Solutions-Hierarchical Solution
B D
A C
•Stands for any P2P key
distribution
•E.g. (A,C) could be
given a unique shared
key
•Better key distributions
are possible

Security Solutions-Hierarchical Solution for
Reducing Storage
A
B
C
D
E
F
G
H
Nodes Treated
as Single Entity
• E.g. (A,B) and (C,D) could share a common key
• If B, needs to communicate with C, this key can be used
• Collusion resistance is an issue

Open Problems
 Problem 1: Secure Admission Control
 For fixed infrastructure networks, how to decide admitting a new node
into the network?
 EAP-TLS, EAP-TTLS are expensive in terms of computation and do not
work well in ad hoc mode
 Access points should be able to handle more decisions to enable easy
roaming
 Need for a scalable but practical solution for admission control especially for
roaming accessibility
 If key management is used dynamics and storage become issues

Open Problems
 Problem 2 : Application Layer Security for fixed infrastructure networks
 Equivalent notions of wired networks.
 Require Light-weight sand boxing mechanisms
 Privacy-preserving light-weight content filtering techniques
 Existing solutions: J2ME KVM, DownloadFun, QualComm
BREW

Open Problems
 Problem 3: Real-time Cell Communication Security
 Key management solutions may not work due to real-
time voice data
 Hacking/tapping cell phones is possible depending on
the encoding scheme used

Open Problems 4
 Certificate mechanisms for nodes
 Certificates in wired networks are
well understood.
 Users typically have better user
interfaces e.g., PC Monitor, allowing
them to examine things like
certificates
 Certificate verification/validation is
tolerable on desktops and even
laptops.

Open Problem 4
 Problem: Not the same for mobile users say, cell phones
 Integrating such features into a cell-phone is difficult
 Expensive to verify certificates due long certification path.
 Solution more difficult for devices with no display or limited display or
regular monitoring of the device, such as sensors.
 Need a different way of handling certificates.

Conclusions
 Situations are more complex in wireless networks, even with
infrastructural support.
 Threats exist at various layers of operation.
 Present solutions to address these threats are not scalable or
not strong enough.
 Simple key management solutions can help.
 But not always.
 Still, lots of interesting and open issues to be solved.

References
 Jean-Pierre Hubaux, Levente, Buttyan and Srdan Capkun “The Quest for
Security in Mobile Ad Hoc Networks”, ACM MobiHOC 2001
 Laurent Eschenauer and Virgil D. Gligor “A Key Management Scheme for
Distributed Sensor Networks” ACM CCS 2002
 Haowen Chan, Adrian Perrig and Dawn Song “Random Key Predistribution
Schemes for Sensor Networks” IEEE Symposium on Security and Privacy 2003
 S.S.Kulkarni, M.G.Gouda and A.Arora “Secret Instantiation in Ad Hoc Networks”
Special Issue of Elsevier Journal of Computer Communication on Dependable
Wireless Sensor Networks, 2006
 Amitanand S. Aiyer, Lorenzo Alvisi, Mohamed G. Gouda “Key Grids: A Protocol
Family for Assigning Symmetric Keys” IEEE International Conference on
Network Protocols, 2006
 B.Bruhadeshwar and Sandeep Kulkarni “An Optimal Symmetric Secret Distribution
for Secure Communication” Michigan State University Technical Report 2008 MSU-
TR-08-196

References
 Bezawada Bruhadeshwar, Kishore Kothapalli: A Family of Collusion Resistant Symmetric
Key Protocols for Authentication. ICDCN 2008: 387-392
 Kishore Kothapalli, Christian Scheideler, Melih Onus, Andréa W. Richa: Constant density
spanners for wireless ad-hoc networks. SPAA 2005: 116-125
 Edmund L. Wong, Praveen Balasubramanian, Lorenzo Alvisi, Mohamed G. Gouda, Vitaly
Shmatikov: Truth in advertising: lightweight verification of route integrity. PODC 2007:
147-156
 Ran Canetti, Adrian Perrig, Dawn Song and Doug Tygar “The TESLA Broadcast
Authenitcation Protocol” RSA Cryptobytes 2002
 Chalermek Intanagonwiwat, Ramesh Govindan, Deborah Estrin, John S. Heidemann, Fabio
Silva: Directed diffusion for wireless sensor networking. IEEE/ACM Trans. Netw. 11(1): 2-
16 (2003)
 Arshad Jhumka, Sandeep S. Kulkarni: On the Design of Mobility-Tolerant TDMA-Based
Media Access Control (MAC) Protocol for Mobile Sensor Networks. ICDCIT 2007:
 General: Wikipedia, WiFi Forum, WiMAX Forum, IETF Website

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