15-01-2013, 03:27 PM
Packet-Hiding Methods for Preventing Selective
Jamming Attacks
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INTRODUCTION
Wireless networks rely on the uninterrupted availability of
the wireless medium to interconnect participating nodes.
However, the open nature of this medium leaves it vulnerable
to multiple security threats. Anyone with a transceiver
can eavesdrop on wireless transmissions, inject spurious
messages, or jam legitimate ones. While eavesdropping and
message injection can be prevented using cryptographic
methods, jamming attacks are much harder to counter.
They have been shown to actualize severe Denial-of-Service
(DoS) attacks against wireless networks [12], [17], [36], [37].
In the simplest form of jamming, the adversary interferes
with the reception of messages by transmitting a continuous
jamming signal [25], or several short jamming pulses [17].
Typically, jamming attacks have been considered under
an external threat model, in which the jammer is not
part of the network. Under this model, jamming strategies
include the continuous or random transmission of highpower
interference signals [25], [36]. However, adopting an
“always-on” strategy has several disadvantages. First, the
adversary has to expend a significant amount of energy
to jam frequency bands of interest. Second, the continuous
presence of unusually high interference levels makes this
type of attacks easy to detect [17], [36], [37].
Conventional anti-jamming techniques rely extensively
on spread-spectrum (SS) communications [25], or some
form of jamming evasion (e.g., slow frequency hopping,
or spatial retreats [37]). SS techniques provide bit-level protection
by spreading bits according to a secret pseudo-noise
(PN) code, known only to the communicating parties. These
methods can only protect wireless transmissions under the
external threat model. Potential disclosure of secrets due
A preliminary version of this paper was presented at IEEE ICC 2010 Conference.
This research was supported in part by NSF (CNS-0844111, CNS-1016943). Any
opinions, findings, conclusions, or recommendations expressed in this paper are
those of the author(s) and do not necessarily reflect the views of NSF.
to node compromise, neutralizes the gains of SS. Broadcast
communications are particularly vulnerable under an internal
threat model because all intended receivers must be
aware of the secrets used to protect transmissions. Hence,
the compromise of a single receiver is sufficient to reveal
relevant cryptographic information.
In this paper, we address the problem of jamming under
an internal threat model. We consider a sophisticated
adversary who is aware of network secrets and the implementation
details of network protocols at any layer in the
network stack. The adversary exploits his internal knowledge
for launching selective jamming attacks in which specific
messages of “high importance” are targeted. For example,
a jammer can target route-request/route-reply messages at
the routing layer to prevent route discovery, or target TCP
acknowledgments in a TCP session to severely degrade the
throughput of an end-to-end flow.
PROBLEM STATEMENT AND ASSUMPTIONS
Problem Statement
Consider the scenario depicted in Fig. 1(a). Nodes A and B
communicate via a wireless link. Within the communication
range of both A and B there is a jamming node J. When A
transmits a packet m to B, node J classifies m by receiving
only the first few bytes of m. J then corrupts m beyond
recovery by interfering with its reception at B. We address
the problem of preventing the jamming node from classifying
m in real time, thus mitigating J’s ability to perform selective
jamming. Our goal is to transform a selective jammer to
a random one. Note that in the present work, we do not
address packet classification methods based on protocol
semantics, as described in [1], [4], [11], [33].
IMPACT OF SELECTIVE JAMMING
In this section, we illustrate the impact of selective jamming
attacks on the network performance. We used OPNETTM
Modeler 14.5 [18] to implement selective jamming attacks
in two multi-hop wireless network scenarios. In the first
scenario, the attacker targeted a TCP connection established
over a multi-hop wireless route. In the second scenario, the
jammer targeted network-layer control messages transmitted
during the route establishment process.
Selective Jamming at the Transport Layer–In the first
set of experiments, we setup a file transfer of a 3 MB file
between two users A and B connected via a multi-hop
route. The TCP protocol was used to reliably transport the
requested file. At the MAC layer, the RTS/CTS mechanism
was enabled. The transmission rate was set to 11 Mbps at
each link. The jammer was placed within the proximity
of one of the intermediate hops of the TCP connection.
Four jamming strategies were considered: (a) selective jamming
of cumulative TCP-ACKs, (b) selective jamming of
RTS/CTS messages, © selective jamming of data packets,
and (d) random jamming of any packet. In each of the
strategies, a fraction p of the targeted packets is jammed.
HIDING BASED ON COMMITTMENTS
In this section, we show that the problem of real-time packet
classification can be mapped to the hiding property of
commitment schemes, and propose a packet-hiding scheme
based on commitments.
Mapping to Commitment Schemes
Commitment schemes are cryptographic primitives that
allow an entity A, to commit to a value m, to an entity
V while keeping m hidden. Commitment schemes are
formally defined as follows [7].
Commitment Scheme: A commitment scheme is a twophase
interactive protocol defined as a triple {X,M, E}.
Set X = {A, V } denotes two probabilistic polynomial-time
interactive parties, where A is known as the committer and
V as the verifier; set M denotes the message space, and set
E = {(ti, fi)} denotes the events occurring at protocol stages
ti (i = 1, 2), as per functions fi (i = 1, 2). During commitment
stage t1, A uses a commitment function f1 = commit()
to generate a pair (C, d) = commit(m), where (C, d) is
called the commitment/decommitment pair. At the end of
stage t1, A releases the commitment C to V . In the open
stage t2, A releases the opening value d. Upon reception
of d, V opens the commitment C, by applying function
f2 = open(), thus obtaining a value of m′ = open(C, d). This
stage culminates in either acceptance (m′ = m) or rejection
(m′ 6= m) of the commitment by V . Commitment schemes
satisfy the following two fundamental properties: