Program Integrity Verification (PIV)

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• Program Integrity Verification (PIV)
• in Wireless Sensor Networks (WSN)
• Based on Park and Shin 2005
• presented by Therese Paul

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Outline

• Introduction to WSN
• Security issues with WSN
• Introduce Program Integrity Verification (PIV)
• Security Framework in PIV
• PIV Architecture
• Distributed Authentication of PIV in WSNs
• Summary
• Reference

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Wireless Sensor Networks (WSN)

• Consists of large numbers of minimum capacity,
  small devices operating in demanding real-world
  environment
• Typically covers a wide area, requiring thousands
  or even millions of sensors, each of which is
  capable of specific functions
• Consists of Sensors, Data-collection Nodes and
  Control Nodes
• For cost and size reasons, sensors are designed
  to minimize resource requirements
• Each device has limited battery energy, memory,
  computation, and communication capacities

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WSN Architecture
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Applications of WSN

• Environmental monitoring and habitat study
• Military surveillance in battle fields
• Condition based maintenance in factories
• Infrastructure health monitoring in buildings
• Precision agriculture, indoor climate control
• Monitoring complex interactions, including
  wildlife habitats, disaster management, emergency
  response, asset tracking, healthcare, and
  manufacturing process flow

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Security Issues in WSN

• Physical attacks on sensor devices, e.g.,
  destroying, analyzing, and/or reprogramming
  sensors
• Service disruption attacks on routing,
  localization, and time synchronization
• Data attacks, e.g., Traffic capture, replaying,
  and spoofing
• Resource-consumption and denial-of-service (DoS)
  attacks

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Security Issues in the Sensor

• Despite the critical role in their intended
  applications, sensor networks are vulnerable to
  various security attacks.
• A captured sensor may be
• Reverse-engineered to figure out what the
  sensors program is supposed to do
• Modified with malicious code
• Abused by the adversary
• Adversary can deploy multiple copies of the
  manipulated sensor device in the network

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Current Solutions

• Make a sensor device tamperproof using
• Code obfuscation - transform the executable code
  to make analysis/modification difficult
• Result checking- examine the validity of
  intermediate results produced by the program
• Self-decrypting programs- store the encrypted
  executables and decrypt them before execution
• Self-checking- within programs, embed codes for
  hash computation as well as correct hash values
  to be invoked to verify the integrity of the
  program under execution

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Current Solution Issues

• Code Obfuscation easier to tamper with the
  program code as the code size in low-cost sensor
  devices shrinks
• Result-Checking/Self-Decryption expensive to
  be employed in resource-limited sensor devices
  because they continuously incurs the overhead of
  verification or decryption, shortening the
  sensors battery lifetime
• The security of self-decrypting programs can be
  easily broken unless the decryption routines are
  protected from reverse-engineering
• All these approaches are unsuitable for sensor
  networks where a program runs on a slow,
  less-capable CPU in each sensor device

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Is There a Better Solution?

• Require each sensor to register itself with a
  dedicated server after verification of its
  program
• Examine and verify the program in sensors as
  needed
• Program Integrity Verification (PIV)
• A protocol that verifies the integrity of the
  program residing in each sensor device when it
• joins the network or
• has experienced a long service blockage

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What PIV Protocol Offers

• Prevents manipulation/reverse-engineering/reprogra
  mming of sensors
• Does not degrade normal sensor functions since
  PIV is triggered infrequently and relies on
  neither self decryption nor result checking
• Purely software-based (and, thus, can be used
  with/without tamper-resistant hardware)
• Tailored to the sensor devices with severe
  resource limitation (e.g., Motes with an 8-bit
  CPU and 4 KB RAM each)

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PIV Security Framework

• PIV consists of PIV Servers (PIVSs) that
  interact with PIV compliant sensors to verify
  programs in the sensors
• Key Management typically hinges on a cluster
  based architecture, in which a cluster-head
  distributes/renews a cluster-specific key
  periodically or whenever a sensor within its
  cluster is found (via PIV) to have been
  compromised
• Intrusion Detection runs on each cluster-head,
  continuously monitors/probes network activities
  to detect malfunctioning devices and, upon
  finding a suspicious device, requests its
  re-verification

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PIV Security Framework Overview
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PIV Components

• PIV Servers (PIVSs)
• equipped with more computation and storage
  capacities than sensor
• examine each sensors program and check if it is
  the same as the original
• maintains a local PIV_DB and stores IDs of the
  sensors belonging to its own cluster
• performs the PIV protocol on a sensor and
  cooperates with other PIVSs in the network to
  update/manage PIV_DB

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PIV Components Contd

• PIV Code (PIVC)
• a special-purpose mobile agent that is generated
  by a PIVS and executed on a sensor being verified
  to read/process the program
• Authentication Server (AS)
• acts as a trusted third party by which the sensor
  can make sure that the PIVS is authentic and,
  hence, it is safe to execute the PIVC
• maintains a list of all legitimate PIVSs in the
  network and updates the list whenever a PIVS is
  added or removed
• authenticates a PIVS using either public-key
  cryptography or a secret authentication key
  shared with each sensor

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PIV Interactions

• The interactions among AS, PIVS, and the sensor
  during PIV consists of the following three tasks
• Authentication of PIVS via AS
• Transmission and execution of PIVC
• Program verification by PIVS/PIVC

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PIV Architecture Details
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The Verification Protocol Between PIVS and Sensor
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The Verification Steps

• Step 1- Initialize This step starts the
  verification protocol between the PIVS and the
  sensor by exchanging their IDs. The sensor, after
  receiving the ID of PIVS, asks an AS for
  authentication of the PIVS and, if the
  authentication fails, terminates the protocol
• Step 2- SendPIVC The PIVS generates a PIVC and
  then sends it to the sensor. It also records the
  time when PIV starts
• Step 3- AckPIVC The sensor sends an
  acknowledgment back to the PIVS
• Step 4- StartPIVC The sensor executes the
  received PIVC

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The Verification Procedure Contd

• Step 5- RequestVerification The PIVC computes a
  hash value on the program by executing and sends
  it back to the PIVS
• Step 6- NotifyVerification The PIVS, if it
  received the hash result within a certain timeout
  period, examines the received hash value to check
  if the program has not been tampered with. If it
  passes the test, the PIVS registers the sensor in
  the PIV_DB. Then, the PIVS notifies the PIVC of
  the verification result
• Step 7- Activate/lock sensor The PIVC, based on
  the verification result, either activates or
  locks the sensor. The sensor state will be
  changed to either ACTIVATED or LOCKED,
  accordingly

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Sensor Verification

• A Randomized Hash Function (RHF)
• Used for computing hash on the program
• For each sensor verification, the PIVS creates a
  new RHF and sends it to the sensor in the PIVC
• Verify the integrity of the program of each
  sensor device by comparing the hash value of the
  sensor program digests maintained in its local
  database with the hash value returned by the
  sensor after calculating it by executing the PIVC
• Only sensors that passed the verification will be
  registered in PIV DB rest will be deleted from
  the database and becoming unable to join the
  network

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State Diagram of a Sensor
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Is PIV Really Secure?

• Sensor Security
• How to Protect the sensor from a malicious
  server/code disguised as a PIVS/PIVC?
• Sensor security is achieved by using the
  authentication server (AS)
• Code security
• How to Protect the PIVC from a malicious sensor?
• Code security by verifying PIVC using the
  Randomized Hash Function (RHF)

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Suggested Improvements to PIV

• Provide Distributed Authentication of PIV
• Eliminates the requirement of the centralized
  authentication server and make PIV a fully
  distributed protocol
• Avoid bottleneck for reliability, security, and
  communication
• Be consistent with the distributed structure of
  sensor networks
• Solution DAPP

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Distributed Authentication Protocol of PIVSs
(DAPP)

• Used by sensors to securely communicate with
  PIVSs without the dedicated and trusted
  Authentication Server (AS)
• DAPP enable sensors to validate a PIVS before
  using it for their verification
• Sensors and PIVSs establishes a pair-wise key and
  for PIVSs to authenticate one another
• Provides a protocol for PIVSs to cooperatively
  detect and revoke malicious PIVSs in the network
• DAPP reduces the sensors communication traffic
  in the network by more than 90 and the energy
  consumption on each sensor by up to 85, as
  compared to the case of using a centralized AS
  for authenticating PIVSs

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DAPP Overview
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Summary

• PIV Offers
• Prevention of manipulation, reverse-engineering,
  and reprogramming of sensors
• Purely software based protection with/without
  tamper-resistant hardware
• Infrequent triggering of the verification
• PIV Protocol security analysis shows that PIV
  effectively defeats possible attacks like replay
  attacks and the only plausible attack requires
  modification of sensor hardware.
• Performance analysis/evaluation demonstrated that
  the communication and processing overheads are
  very small
• The hash computation algorithm has a small time
  overhead

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Reference

• Soft Tamper-Proofing via Program Integrity
  Verification in Wireless Sensor Networks By
  Taejoon Park, Student Member, IEEE, and Kang G.
  Shin, Fellow. IEEE TRANSACTIONS On Mobile
  Computing, Vol. 4, No. 3, May/June 2005
• Distributed Authentication of Program Integrity
  Verification in Wireless Sensor Networks By
  Katharine Chang, Kang G. Shin. Proceedings of
  2nd International Conference on Security and
  Privacy in Communication Networks (SecureComm),
  Baltimore, MD 2006 IEEE
• Secure Routing In Wireless Sensor Networks
  Attacks And Countermeasures By Chris Karlof and
  David Wagner. University of California at
  Berkeley, Berkeley, CA 94720, USA
• Wireless Sensor Networks By F. L. Lewis. Smart
  Environments Technologies, Protocols, and
  Applications ed. D.J. Cook and S.K. Das, John
  Wiley, New York, 2004.

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Questions??