One document matched: draft-zhou-rrg-lp-wsn-00.xml


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  <front>
    <title abbrev="CTA">The Location Privacy of Wireless Sensor Networks:
    Attacks and Countermeasures</title>

    <author fullname="Lin Zhou" initials="L" surname="Zhou">
      <organization>SouthEast University</organization>

      <address>
        <postal>
          <street>SouthEast University,Nanjing,210012</street>
        </postal>

        <email>573823136@qq.com</email>
      </address>
    </author>

    <author fullname="Jie Huang" initials="J" surname="Huang">
      <organization>SouthEast University</organization>

      <address>
        <postal>
          <street>SouthEast University,Nanjing,210012</street>
        </postal>

        <email>jhuang@seu.edu.cn</email>
      </address>
    </author>

    <date day="28" month="May" year="2014"/>

    <abstract>
      <t>With the related applications of wireless sensor networks getting
      into our lives quickly, the research of WSN is growing more and more
      necessary. The most significant problem which threatens the successful
      deployment of sensor systems is privacy, there are many protocols
      providing the security of news content for the WSNs. However, due to the
      open feature of sensor networks, context information is still in an
      exposed state, which makes the network be vulnerable to traffic analysis
      attack and hop by hop tracing back packet attack. Thus location privacy
      protection programs have been proposed. In this paper, we analyze and
      compare the existing major schemes comprehensively, meanwhile illustrate
      their theoretical models, principles and the advantages and
      disadvantages in detail.</t>
    </abstract>
  </front>

  <middle>
    <section title="Introduction">
      <t>With the rise of Internet of things, wireless sensor network (WSN)
      which is an integral part of Internet of things have a very broad
      application prospects.</t>

      <t>WSNs consist of a large number of micro sensor nodes, those nodes are
      capable of sensing information, computing and communicating. However,
      due to the low cost of these nodes, the storage capacity of battery is
      small, the computing capability of node processors is low, and the
      communication of wireless communication device is limited. Overall
      wireless sensor networks have the following characteristics:
      large-scale, self-organizing, multi-hop routing, dynamic,
      resource-constrained and applications related. These features make the
      wireless sensor networks have broad application prospects in military,
      environment, medical treatment, smart home.</t>

      <t>Wireless sensor networks could be used to collect sensitive
      information or deployed in hostile or unprotected environment, which
      make protecting the privacy of sensor nodes be crucial in the current
      WSNs, the privacy issues in WSNs are divided into two categories:
      content privacy and context privacy. In order to solve the problem of
      content privacy, for now, many encryption and authentication
      mechanisms<xref target="RFC4948"/><xref target="RFC4949"/>have been
      proposed and used, and can basically meet the corresponding
      requirements. But due to the open feature of WSNs, the exposure of
      context information can cause the user's secret leak to the attacker,
      especially attacker can locate the source node or destination node (base
      station) through traffic analysis and hop track packet stream. The
      location of source node and base station are very sensitive in many WSN
      applications such as in precious animals detection system, the position
      of animals (source node) can’t be exposed to illegal hunters; in
      battlefield information collection system, the position of soldier (sink
      node) who accepts a variety of information can’t be exposed to the
      enemy. Because of the importance and necessity of location privacy, this
      paper has a research on principles, advantages and disadvantages of
      current main location privacy protection agreement (PhR<xref
      target="PhR"/>(GROW<xref target="GROW"/>, PRLA <xref target="PRLA"/>),
      PUSBRF<xref target="PUSBRF"/>, LPR <xref target="LPR"/>, LPSS<xref
      target="LPSS"/>, DEFP<xref target="DEFP"/>).</t>

      <t>Based on the property of object which needs to be protected, this
      paper divides the possible attackers into two categories: the attackers
      who attack source node and the attackers who attack sink node, and
      establishes corresponding models according to their individual features.
      According to the attacker models we propose appropriate protection
      agreements and discuss their advantages and disadvantages.</t>

      <t>The main contributions of this paper are as follows:</t>

      <t>(1) We divide possible attackers into two categories based on the
      property of object which needs to be protected for the first time, and
      establish the corresponding attack models;</t>

      <t>(2) We put forward the corresponding settlement agreements in
      accordance with attack models on the basis of scientific ideas that
      discovering problems then solving them, meanwhile we conduct
      comprehensive analyses and comparisons on the main location privacy
      protection agreements systematically for the first time;</t>

      <t>(3) We summarize the maximum intensity attacker that each privacy
      protection agreement can handle by analyzing and comparing, then
      conclude the respective applicable scenario of each agreement.</t>
    </section>

    <section title="The Attack Models">
      <t>The objects protected in WSNs are usually the source node (such as in
      precious animals detection system, the position of the node which has
      monitored animals can’t be exposed to illegal hunters) and the sink node
      (such as in battlefield information collection system, the location of
      the last node which is responsible for transferring a variety of
      information to the soldiers can’t be exposed to the enemy). According to
      the property of object which needs to be protected we divide possible
      attackers into two categories: the attackers who attack source node
      (source attackers) and the attackers who attack sink node (sink
      attackers). This article assumes that two types of attackers both have
      the following characteristics: ① attackers have excellent hardware,
      sufficient storage space and powerful computation ability; ② attackers
      can detect traffic only in one region, but are not capable of decrypting
      data packets <xref target="PRLA"/>; ③ attackers can only trace the nodes
      sending data packets but the nodes receiving data packets.</t>

      <section title="The Model of Source Attackers">
        <t>The process of attacker tracing back source node’s location is
        described as follows: the attacker starts monitoring at the sink node,
        when monitored a message, he can deduce that the signal is issued by
        node A through wireless signal positioning device, then moves
        immediately to node A to continue to wait, when a new message received
        he determines that it was issued by node B and then quickly moves to
        node B, repeat this process can trace to the location of the source
        node.</t>

        <t>This paper divides the source attackers into two categories based
        on the sources attackers' tracking method: the patient source attacker
        and the careful source attacker.</t>

        <t>The model of patient source attacker is described as follows: the
        attacker follows a simple and natural attack strategy: he starts on
        the position of sink node (base station) to wait until a new message
        is heard, and then immediately move to the node that generated the
        message, repeat this process until the location of the source node is
        traced.</t>

        <t>The model of cautious source attacker is described as follows:
        because some privacy protection technology [3] could lead an attacker
        to strand at a location remote from the real source node, the strategy
        of cautious source attacker is limiting the eavesdropping time in one
        position, if he has not received any new messages within a specified
        time interval, he thinks that he was misled to current position, and
        then hops back to the previous position to continue listening.</t>
      </section>

      <section title="The Model of Sink Attackers">
        <t>Sink attackers determine which nodes are on the transmission path
        according to the time sequence of date packet transmission, then
        mobile hop by hop, and finally get to the sink node. The process of
        attacker tracking sink node's position is described as follows:
        assuming the attacker listening for message transmitting within the
        range of one hop at node C, he monitors that node C sends a data
        packet at first, then node B transmits a data packet subsequently, the
        attacker moves to the node B immediately and infers that the
        transmission path at this time is C to B, according to this method,
        the attacker tracks the location of the nodes which are one hop from
        the base station as having captured the sink node.</t>

        <t>Similarly sink attackers are also divided into two categories: the
        patient sink attacker and the cautious sink attacker. The principle of
        their attacker model is similar to the principle of corresponding
        source attacker model, not repeat them.</t>
      </section>
    </section>

    <section title="Location Privacy Protection Agreements">
      <t>In order to prevent these attackers from destroying the location
      privacy security of wireless sensor networks, a series of security
      protocols are proposed, such as: phantom routing (PhR), source location
      privacy preservation protocol in wireless sensor networks using
      source-based restricted flooding (PUSBRF), location-privacy routing
      protocol (LPR), location privacy support scheme (LPSS), differential
      enforced fractal propagation (DEFP). This section will classify these
      main protocols and describe the principle of each protocol in
      detail.</t>

      <t>In this paper, we divide the main privacy and security protocols
      which are mentioned above into three categories: source location privacy
      protection protocols, sink location privacy protection protocols and
      both location privacy protection protocol. Source location privacy
      protection protocols include: PhR, PUSBRF; sink location privacy
      protection protocols include: LPR, DEFP; and both location privacy
      protection protocol includes LPSS.</t>

      <section title=" Source Location Privacy Protection Protocols">
        <section title=" Phantom Routing (PhR)">
          <t>Take the panda-hunter model<xref target="PhR"/> for example, the
          description of phantom routing is decribed as follows: in PhR , the
          transmission of each information goes through two phases:① the
          random walk phase , may be a pure random walk or a directional walk
          (based on sector or hop count between the node and the sink
          node<xref target="PhR"/>);② subsequent flooding/single-path routing
          phase, which will send the information to the sink. When the source
          node sends a message, the message is unicasted Hwalk hops randomly,
          then pass it to the base station based on the baseline (probability)
          flooding<xref target="SECH"/>or single-path routing<xref
          target="PhR"/>. Because of PhR, after an attacker intercepted
          messages i he will wait a long time before receiving the next
          message i+1, when he finally receives the message i+1, the instant
          sender of this message may lead the attacker to the position which
          is away from the true source node.</t>

          <t>On the basis of phantom routing (PhR) also proposed the phantom
          routing with location angle (PRLA)<xref target="SECE"/>, PRLA is
          consist of three phases:① the sink node floods a query message in
          the whole network, so that each node can creates the shortest path
          to the sink and divides its neighboring nodes into two direction
          collections according to the distance between neighboring nodes and
          the sink;② the source node produces a limited flooding with the
          range of random walk, this process makes each node can get the
          inclination angle of respective neighboring nodes and calculate the
          transmitting messages possibility of each neighboring node;③ the
          source node sends date packets to the sink node, each data packet
          will be transmitted Hw hops in a random walk way based on the
          inclination angle, then along the shortest route path goes to the
          sink node from the phantom source node.</t>

          <t>PRLA is essentially an improvement of PhR's random walk phase, to
          a degree it avoids the generation of the offset path<xref
          target="PUSBRF"/>, on the basis of PhR it further improves the
          safety time.</t>

          <t>Greedy random walk (GROW) is essentially an improvement of PhR's
          random walk phase too, in GROW, the sensor node each time selects a
          neighboring node from those who did not participate in the random
          walk phase, in this way, random walking is always trying to cover a
          area where hasn't accessed to by greedy strategy<xref
          target="GROW"/>, thereby improving the ability of sensor networks
          against attackers.</t>
        </section>

        <section title=" Protocol Using Source-based Restricted Flooding (PUSBRF)">
          <t>PUSBRF protocol is consist of four phases:① network security
          initialization phase;② source node h hops limited flooding phase;③ h
          hops directional routing phase, the direction of each hop is
          selected by the current node based on the minimum hop value that its
          neighboring apart from the source node;④ the shortest path routing
          phase.</t>

          <t>The process of network initialization phase is described as
          follows: complete the establishment of the key, discover the
          neighboring nodes to achieve the information of minimum hop value
          that each ordinary nodes apart from the base station, and each node
          pre-loads the following parameters: the public key (Kpub) used for
          message encryption, the list of neighboring nodes (Tu), hop value h,
          then generate a base-station broadcast in the whole network, the
          base station broadcasts the initialization message
          BM={BRO_BASE,ID,hop_bs} in the entire network, in which BRO_BASE
          indicates the type of messages, ID indicates the identity of the
          node that sent the message, hop_bs indicates the hop count of the
          message which is initially 0., PRLA is consist of three phases:① the
          sink node floods a query message in the whole network, so that each
          node can creates the shortest path to the sink and divides its
          neighboring nodes into two direction collections according to the
          distance between neighboring nodes and the sink;② the source node
          produces a limited flooding with the range of random walk, this
          process makes each node can get the inclination angle of respective
          neighboring nodes and calculate the transmitting messages
          possibility of each neighboring node;③ the source node sends date
          packets to the sink node, each data packet will be transmitted Hw
          hops in a random walk way based on the inclination angle, then along
          the shortest route path goes to the sink node from the phantom
          source node.</t>

          <t>The process of the source node h hops limited flooding phase is
          described as follows: it makes the source node realize the broadcast
          in whole network within h hops, each node which is in the rage of h
          hops from the source node gets the minimal distance between itself
          and the source, then in list Tu adds the minimal hop value that the
          neighboring nodes away from the source node and records the
          value.</t>

          <t>The phantom source nodes generated in h hops directional routing
          phase are far enough away from the real source node and their
          location is diverse. The shortest path routing achieves transmitting
          packets from the phantom source node to the base station in a
          shortest period of time.</t>
        </section>
      </section>

      <section title=" Sink Location Privacy Protection Protocols">
        <section title=" Location-privacy Routing Protocol (LPR)">
          <t>Because the goal of routing protocols is to transmit a packet
          along the shortest possible path to the destination, the packets’
          forwarding direction is always pointing to the receiver. Then the
          attacker will determine the wright node which the real package goes
          to according to the general trend of path. In order to resist this
          kind of problem LPR protocol has been proposed.</t>

          <t>LPR randomizes routing path, so that the forward direction of
          packages does not always point to the receiver. The route consists
          of two phases: ① each sensor node divides his neighboring nodes into
          two lists: a closer list which is consist of the neighboring nodes
          whose distance to the destination is shorter than its own; a further
          list which is consist of the neighboring nodes whose distance to the
          destination is longer than equal to its own, the specific
          classification criteria refer to the literature <xref
          target="LPR"/>. ②When a sensor node forwards a date packet, he
          chooses a neighbor node in one of the two lists randomly as the next
          hop node of the package, and the selection probability from the
          further list as the next hop node is Pf, so the selection
          probability from the closer list as the next hop node is 1-Pf.</t>
        </section>

        <section title="Differential Enforced Fractal Propagation (DEFP)">
          <t>DEFP is a simple distributed algorithm based on DFP<xref
          target="DEFP"/>. The key idea of the program is to leave early
          packet forwarding nodes have a higher chance of false packet
          transmission in the next phase, at the beginning DEFP allocates one
          vote to every neighboring node. When a node selects one of his
          neighboring nodes as the next node which is false packets forwarded
          to, the votes of the node increase k. According to this approach,
          after using lottery scheduling algorithm <xref target="SECH"/>, when
          a node has forwarded a fake packet to one of its neighboring nodes,
          it will continue to forward other fake packets to the same
          neighboring node with rising probability.</t>
        </section>
      </section>

      <section title="Both Location Privacy Protection Protocols">
        <t>The program consists of two phases:① Each sensor node divides his
        neighboring nodes into three sets: a small gradient <xref
        target="SECT"/>set comprised of the neighboring nodes with smaller
        gradient value; an equivalent gradient set comprised of the
        neighboring nodes with the same gradient value; a large gradient
        comprised of the neighboring nodes with larger gradient value. ② When
        a neighboring node transmits a packet, he selects the next hop node
        from the equivalent gradient set with the probability Pi, or selects
        the next hop node from the small gradient set with the probability
        1-Pi. LPSS also can be used combine with the fake package
        strategy.</t>
      </section>
    </section>

    <section title="Performance Comparison">
      <t>This section compares the performance of the location privacy
      security protocols mainly by three parameters: security strength (safety
      time), transmission delay, communication overhead.</t>

      <t>(1) Safety time (privacy protection strength): the number of packages
      sent by the source node before the target node exposed to the enemy
      (before hunters capturing the panda or enemy discovering soldiers who
      receive information), the more of packages be sent the longer of safety
      period, conversely the shorter of safety period;</t>

      <t>(2) Energy loss (communication overhead): the average hop value
      through which the data packet sent by the source node eventually arrives
      at the sink node (base station), and the lager of the hop value the
      greeter of communication overhead, conversely the smaller of
      communication overhead;</t>

      <t>(3) Propagation delay (transmission delay): the period in which the
      data packet sent by the source node eventually arrives at the sink node
      (base station), obviously lager of the average hop value the longer of
      transmission delay, conversely the shorter of transmission delay.
      Combining with the consequence in (2) can easily conclude that the
      communication overhead is proportional to transmission delay.</t>

      <t>In order to facilitate the comparison, source location privacy
      protection protocols all use the same simulation configuration: in the
      OMNet<xref target="SECT"/>simulation environment, we distribute 10000
      sensor nodes uniformly in the network with area of 6000*6000 m2, in
      which the communication radius of each node is 110m. So the average
      number of neighboring nodes of each node is 8.64, weakly connected nodes
      (node number of neighboring nodes is less than or equal to 3) account
      for only about 1%, the attackers begin tracking from the base
      station.</t>

      <t>The communication overhead is closely related to two parameters: the
      hop value of random walks and the distance between the source node and
      the base station. When research the changing trend with one parameter,
      we need to assume the other parameter as a fixed value. Assume that the
      distance between the source node and the base station are 60 hops, the
      relationship between communication overhead and hop count of random
      directional walks shows that:① With the number of random directional
      hops increasing, the communication overhead (average transmission delay)
      of PhR and PUSBRF both increase. This is because with the number of
      random directional hops increasing, date packets need forward more times
      during random routing phase to reach phantom source nodes, however, this
      phase doesn't make contribution to pass packets to the base station,
      thus their communication overhead improves.② When the random directed
      hop value is fixed, the communication overhead of PUSBRF is slightly
      higher, because the directed walk of PhR is based on the number of hops
      between the node to the base station, so PhR only need the base station
      broadcast in the whole network, but from the above mentioned phases of
      PUSBRF protocol we can see, PUSBRF requires not only the base station
      broadcast in the whole network but also needs the source node broadcast
      in the whole network within h hops.</t>

      <t>Make the value of random directional hops as h=15, then the trend of
      the two protocols between the communication overhead and hops from the
      source node to the base station shows that: ① the communication overhead
      (average transmission delay) of PhR and PUSBRF both increase with the
      distance between the source node and the base station increasing. This
      is because with increasing distance between the source node and the base
      station, the data needs to go through more hops to reach the base
      station.② when the hop value of two protocols between the source node
      and the base station are the same, the communication overhead of them
      are about the same.</t>

      <t>(3) The security period is closely related to two parameters: the
      value of random directional hops and the distance from the source node
      to the base station. Assume that the distance between the source node
      and the base station are 60 hops, then the trend of the security period
      and the random directional hop value shows that: ① The security period
      of PhR and PUSBRF both increase with h increasing. This is because the
      increasing h makes the distance between the phantom source nodes
      generated by two protocols and the real source node further, then
      generates more random paths which make the source attackers more
      difficult to trace. ② When the random directional hop value are the
      same, the security period of PUSBRF is much longer than PhR's, this
      indicates that the safety performance of PUSBRF is better than PhR's.
      This is because phantom source nodes generated by PUSBRF are more
      diverse geographically than which are generated by PhR<xref
      target="PRLA"/>.</t>

      <t>Make the value of random directional hops as h=15, the trend of the
      security period and the distance from the source node to the base
      station shows that: ① With the increasing of the hop count between the
      source node and the base station, the security period of PhR and PUSBRF
      also increases. This is because when the hop count is larger, the more
      hops that source attackers need to trace back to the real source node. ②
      When the hop count between the source node and the base station of two
      protocols are the same, the safety performance of PUSBRF is better than
      PhR's, indicating that the safety performance of PUSBRF better than PhR,
      the reason is the same as above.</t>

      <t>The performance comparison of above two protocols and LPSS used with
      fake packets shows that: the safety performance of pure LPSS is between
      PhR and PUSBRF, so are communication overhead and transmission delay,
      when LPSS is used with the false packet strategy, the safety time
      increased substantially and the communication overhead becomes larger,
      but the transmission delay is still close to pure LPSS protocol, which
      is because the transmission paths of true packets are the same with pure
      LPSS, fake packets just used to confuse attackers, and don’t affect the
      transmission of true packets.</t>

      <t>In summary, compared to the pure flooding and single- path routing,
      PhR can resist the attacker's packet tracing attack to some extent, but
      the phantom source nodes generated by PhR concentrate in one area with
      high probability; PUSBRF protocol makes up this deficiency, it can
      generate phantom source nodes which are geographical diversity with
      equal probability, and enhance the security of the source node's
      location privacy effectively, however the improvement of security period
      at the cost of increasing of communication overhead, so the
      communication overhead of PUSBRF is more than PhR's, the transmission
      delay is longer too, and can't weigh between the security period and the
      communication overhead; gets the weigh between security period and
      transmission delay by adjusting the value of the parameters Pi. When
      LPSS is used combines with false packet strategy, it can achieve
      impressive safety performance, but at the cost of communication overhead
      increasing.</t>

      <t>The above three protocols can withstand source attackers (including
      patient source attackers and cautious source attackers), and are more
      resistant to cautious source attackers<xref target="SECW"/>, their pros
      and cons make we should select the appropriate protocol according to
      specific application requirements.</t>

      <t>The simulation results of location privacy protocols which can
      protect the sink node (base station) are shown as follows:</t>

      <t>In order to facilitate the comparison, sink location privacy
      protection protocols all use the same simulation configuration: in the
      OMNet simulation environment, we distribute 2500 sensor nodes uniformly
      in a sensor network, make the average number of neighboring nodes of
      each node be 8, and attackers began tracking from the source node.</t>

      <t>(1) At the packet forwarding phase LPR protocol selects the next hop
      node from the further list with probability Pf, and get the trend
      between the transmission delay and hop count from the source node to the
      sink node of pure LPR when Pf is 0.0%, 25%, 37.5%, meanwhile compare
      with DEFP. The resulet showa that: ① with the increasing of distance
      between the source node and the base station, the transmission delay of
      two protocols both increase. This is because when the source node is far
      away from the base station, sink attackers at the source node need to
      track more hops to reach the base station;② when the distance from the
      source node to the base station are the same in LPR, the transmission
      delay increases with the increasing of Pf. This is because Pf is the
      probability with which we select the next hop from the further list, the
      larger of Pf the more likely to choose the next hop from the further
      list, which extends the transmission path;③ when the distance between
      the source node and the base station are the same, the transmission
      delay of LPR is longer than DEFP's.</t>

      <t>(2) The trend between security period and Pf of pure LPR protocol and
      compare with DEFP shows that: ① with the increasing of Pf, the security
      period of LPR increases. This is because Pf is the probability with
      which we select the next hop from the further list, the larger of Pf the
      more likely to choose the next hop from the further list, which extends
      the transmission path, so sink attackers need trace a longer time to
      reach the base station;② the security period of LPR is longer than
      DEFP's, and the larger of Pf, the higher amplitude of LPR's security
      period longer than DEFP's.</t>

      <t>The performance comparison of above two protocols with fake packets
      strategy, pure LPSS and LPSS with fake packets strategy indicates that:
      when DEFP, LPR, LPSS all used with fake packets strategy, the security
      period of three protocols all improving, the transmission delay remain
      constant, but the energy consumption increasing.</t>

      <t>In summary, LPR can get the balance between privacy protection
      strength (security period) and energy consumption by adjusting Pf, LPR
      with fake packets strategy can effectively improve the safety
      performance of the program compared with DEFP, but its transmission
      delay and communication overhead are far greater than DEFP's, LPSS get
      the trade-off between transmission delay and security period by
      adjusting Pi, and with the increasing of hop counts between the source
      node and the sink node, the safety strength (security period)of LPSS
      increases evidently dramatically than LPR, but LPSS can only play full
      advantage when it is used with fake packets strategy, otherwise it isn't
      superior than LPR and DEFP comprehensively.</t>

      <t>The above three protocols can resist sink attackers (including of
      patience sink attackers and cautious sink attackers), and they all have
      their pros and cons, we need select the appropriate protocol according
      to specific application requirements.</t>
    </section>

    <section title="Security Consideration">
      <t>This paper divides attackers into two types based on the properties
      of the objects which need be protected: source attackers and sink
      attackers, then establishes corresponding attack models, after that we
      propose appropriate protocol in accordance with attack models, including
      phantom routing (PhR), source location privacy preservation protocol in
      wireless sensor networks using source-based restricted flooding
      (PUSBRF), location-privacy routing protocol (LPR), location privacy
      support scheme (LPSS), differential enforced fractal propagation (DEFP).
      At last we have comprehensive analysis and comparison of these location
      privacy protection protocols systematically, mean while sum up the
      advantages and disadvantages of each protocol.</t>
    </section>

    <section title="IANA Consideration">
      <t> To be completed. </t>
    </section>
  </middle>

  <back>
    <references>
      <reference anchor="RFC4948">
        <front>
          <title>Spins: security protocols for sensor networks</title>

          <author fullname="A.Perrig" initials="A" surname="Perring"/>

          <author fullname="R.Szewczyk" initials="R" surname="Szewczyk"/>

          <author fullname="D.Tygar" initials="D" surname="Tygar"/>

          <author fullname="V.Wen" initials="V" surname="Wen"/>

          <author fullname="D.Culle" initials="D" surname="Culle"/>

          <date month="May" year="2007"/>
        </front>
      </reference>

      <reference anchor="RFC4949">
        <front>
          <title>A key-management scheme for distributed sensor
          networks</title>

          <author fullname="L.Eschenaur" initials="L" surname="Eschenaur"/>

          <author fullname="V.Gligor" initials="V" surname="Gligor"/>

          <date month="August" year="2007"/>
        </front>
      </reference>

      <reference anchor="PhR">
        <front>
          <title>Enhancing source location privacy in sensor network
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  </back>
</rfc>

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