TinySec : Link Layer Security Architecture for Wireless Sensor Networks

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TinySec Link Layer Security Architecture for
Wireless Sensor Networks

• Chris Karlof Naveen Sastry David Wagner
• Presented by Anil Karamchandani
• 10/01/2007

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What is ???

Tiny OS
Link layer
Wireless Sensor Network
Tiny Sec
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Contents

• Motivation TinySec
• Contributions by the paper .
• Difference between Sensor Networks and Other
  Networks .
• Security threats in WSN.
• What is TinySec and its goal .
• Why Link Architecture .
• Design Goals .
• Security Primitive.
• Design of TinySec .
• Modes of Encryption and their drawbacks.
• Security Analysis of TinySec .
• Implementation and Evaluation.

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What was the motivation ???

• Sensor Networks Resource Constraint networks ,
  small memory , weak processor , limited energy ,
  less Bandwidth .
• 80 of all 802.11 wireless networks operate in
  the clear i.e. without cryptographic protection
• Need for an architecture which could change
  things around. TinySec
• SW / HW

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Contributions of this paper

• To introduce TinySec as a protocol for link layer
  cryptography in Sensor Networks.
• To Measure the bandwidth , latency and energy
  costs of TinySec .
• To encourage people to volunteer and perform
  research in further higher level of protocols.

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What is the Difference between WSN and other
Network ?

• WSN

• Other Networks

• Bandwidth - less
• Devices have very little computational power
• Energy is less with Wireless Sensor devices
• Wireless Networks are difficult to protect
• Vulnerable to resource consumption
• Information Hop by Hop .

• Bandwidth more
• Comparatively devices have more computational
  power.
• Energy for devices in other networks is high.
• Comparatively much easier to protect .
• Not Vulnerable to resource consumption.
• Information- end to end (not necessary for all
  networks)

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Security Threats in WSN

• WSN are difficult to protect .
• WSN are in a Broadcast medium
• WSN are vulnerable to resource consumption
  attacks .
• Intruders can waste network bandwidth

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What is TinySec and its Goal

• Lightweight link layer Security Mechanism for
  Sensor Networks .
• Goal Is to minimize the overhead with
  reasonable protection from
• Energy
• Bandwidth
• Latency

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Why Link Architecture ???

• Conventional networks authenticity and
  integrity , confidentiality end to end
  mechanism (SSH , SSL).
• End to end Security is vulnerable to DOS (Denial
  of Attacks).
• Message integrity should not be checked at the
  end alone.

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Design Goals

• Security
• Access control
• Message integrity
• Message confidentiality
• Performance
• Energy
• Bandwidth
• etc.
• Ease of use

• MESSAGE AUTHENTICATION CODE
• ENCRYPTION
• DECREASE MESSAGE LENGTH
• PUT IN TinyOS

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Security Primitive

• Message Authentication code
• A cryptographic checksum for checking the message
  integrity
• MAC

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Security Primitives (cont .)

• Encrypting the same plain text two times should
  get two different cipher texts
• Initialization Vectors ( IV)
• -A side input to the Encryption Algorithm
• -Not kept secret , sent with the message .

shared key
shared key
MESSAGE
(YES/NO)
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Why design TinySec ??

• Why Design TinySec when existing protocols are
  present .
• - IPSec ,SSL / SSH are too heavy weight to be
  used in Sensor Networks .
• -The packet format adds many bytes of overhead
  and they were not being designed to built on WSN.

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Design of TinySec

• Two different security Options
• --Authentication Encryption TinySec AE
• --Authenticated only TinySec Auth
• In both the cases the data is authenticated with
  MAC and thus maintaining Data Integrity.

encrypted
Header
Message
MAC
Header
MACs
Message
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How can we Encrypt ??

• Requirements for encryption
• To select an encryption scheme
• To specify the IV format
• 8 Byte IV format

CIPHER BLOCK CHAINING CBC
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Different modes of Encryption

• A stream Cipher uses a Key and IV .
• Together they are ex-ored with message to get the
  cipher text (C MK.IV).
• Drawbacks - If same IV is used to encrypt 2
  different packets then there is a possibility of
  retrieving both the packets.

Symmetric key encryption schemes
Modes of operation using block cipher
Stream Ciphers
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What is CBC mode of Encryption??

• Link
• In (CBC) mode, each block of plaintext is XORed
  with the previous ciphertext block before being
  encrypted.
• This way, each ciphertext block is dependent on
  all plaintext blocks processed up to that point.

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Drawbacks of CBC Mode .

• Given two plaintexts P and P .If the IV used
  for the two plaintexts are same then there exists
  a possibility that the length of the longest
  shared message is shared / known .

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How does the packet format for TinySec Looks like
??
Dest Destination address AM Active Message
Handler type L length of the data Src source
of the address
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Security Analysis of TinySec Message Integrity
and Authenticity

• Security of a CBC MAC is proportional to the
  length of the MAC .
• Choice of 4 bytes MAC ??

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Implementation of TinySec

• Implemented on Berkeley Sensor Nodes
• Integrated into TOSSIM simulator
• 3000 Lines of nesC code
• Works in FIFO format
• Thus TinySec has got 2 priority Schedulers

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Evaluation

• Energy Consumption
• Power Consumption
• Bandwidth
• - Energy 24 bytes of data was transmitted

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Evaluation
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Evaluation (Cont)

• Since the power consumed by TinySec-AE is maximum
  ( for majority of time )the energy consumed by
  TinySec AE will also be maximum
• While sending with TinySec the packets are also
  larger in length

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Bandwidth

• To measure Bandwidth- 24 bytes packets were sent
  using TinyOS , TinySec Auth , Tiny-Auth Enc .
• Measured the number of packets that were
  successfully received .

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Conclusions

• We have learnt that there are design
  vulnerabilities in the conventional protocols for
  sensor networks.
• TinySec addresses this with extreme careful
  design and takes advantage of the limitations of
  Sensor Networks

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References

• http//www.webopedia.com/quick_ref/OSI_Layers.asp
• http//camars.kaist.ac.kr/hyoon/courses/cs710_200
  4_fall/rhoyo.ppt
• http//en.wikipedia.org/wiki/Block_cipher_modes_of
  _operationCipher-block_chaining_.28CBC.29