Security Considerations for

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21 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Security Considerations for Wireless Sensor Networks

Prabal Dutta

dutta.4@osu.edu

(614) 975
-
3658

Security Considerations for

Wireless Sensor Networks

Security Considerations for Wireless Sensor Networks

Overview


Motivation


Basic Concepts


Confidentiality


Authentication & Non
-
repudiation


Integrity


Freshness


Challenges


Key Distribution Strategies


Constraints


Others


Take Away

Security Considerations for Wireless Sensor Networks

Motivation


This Presentation


Introduction to security concepts for 1451.5 survey


In General


Wireless Sensor/Actuator Networks may be
collecting sensitive data and controlling important
assets that must be protected


Wireless is a broadcast medium so inherently
insecure and subject to eavesdropping


Vulnerable to active attacks like message spoofing
or message replays


Obscurity IS NOT security


MUST have security for a complete solution

Security Considerations for Wireless Sensor Networks

Confidentiality


Allows communicating parties to keep secrets


Protects against eavesdropping


Implemented through encryption using
ciphers


Private (“Shared”) Key (Symmetric Cipher)


Fast, small, efficient, but has a key distribution problem


Public Key (Asymmetric Cipher)


Solves key distribution, but computationally very
expensive


But encryption is not enough


if the same
message encrypts to the same cipher text


then replay attacks are possible (“freshness”)

Security Considerations for Wireless Sensor Networks

Authentication & Non
-
repudiation


Related concepts that allow a message
recipient to verify the authenticity of the
message source


Allow a party to prove its identity


Protects against forgery or masquerade


If a priori knowledge of peer (and a shared
secret) exists, then use of knowledge of
shared secrets is sufficient


Otherwise, requires use of a digital signature
from a trusted source (like a notary public)


Digital Signatures implemented using a
member of the public key cryptography suite
(
e.g.

DSA)
-

but computationally expensive

Security Considerations for Wireless Sensor Networks

Integrity


Ensures that:


Messages are not accidentally corrupted by an
imperfect communications channel


Message are not intentionally corrupted by an
attacker during transmission


Typically implemented through cryptographic
hashes that are similar to a CRC.


Hashes are considerably more complex than
a CRC function, and therefore practically
impossible to reverse engineer.


Common hashes include MD5 and SHA

Security Considerations for Wireless Sensor Networks

Freshness


Ensures that:


Messages are current


Messages are ordered


Messages are not duplicates (replays) of a
previously transmitted message


Weak freshness provides partial message
ordering but no delay information


Strong freshness provides complete ordering
and delay estimation


Implemented through sequence numbers,
timestamps, etc.

Security Considerations for Wireless Sensor Networks

Key Distribution Strategies


Shared Global Key (pre
-
deployment)


Frequently used


Compromised node compromises entire network


Shared Pair
-
wise Keys (pre
-
deployment)


Requires n(n
-
1)/2 ~ n^2 keys


Compromised node compromises entire network


New node requires n + 1 new keys n + 1 updates


Ad Hoc Pair
-
wise Keys (post
-
deployment)


Computationally expensive (D
-
H KE: 2.24 J in 5.75 sec on
206MHz SA [Hodjat]
-
> 1850 reps on CR2450 battery)


Vulnerable to DoS Attacks


Base Station Key Distribution Center (pre & post)


Pair
-
wise keys between nodes and BS (Kerberos
-
like)


Ad hoc pair
-
wise keys between nodes with BS help

Security Considerations for Wireless Sensor Networks

Constraints


Limited source of energy


Limited computational resources


MHz


FLOPS


Code size


RAM size


Limited communications bandwidth


Asymmetric ciphers (
e.g.

RSA) and key
exchange protocols (
e.g.

Diffie
-
Hellman) are
computationally expensive


Security Considerations for Wireless Sensor Networks

Other Challenges


Cipher Selection


Must be small, fast, and readily available


Global Clock Synchronization


Required for certain functions like freshness


Authenticated Broadcast [TESLA, TIK]


One node simultaneously broadcasts
authenticated

message to several other nodes


Also requires clock synchronization


Static vs. Mobile Nodes


Mobility adds another dimension of complexity to
key distribution

Security Considerations for Wireless Sensor Networks

Take Away


Many constraints & tradeoffs and nothing
comes for free



Energy is biggest constraint



Key exchange is a major challenge



No “one
-
size
-
fits
-
all” solution



Active area of academic research


Berkeley, UCLA, Network Associates, others