TinySec : Link Layer Security Architecture for Wireless Sensor Networks

1. TinySec : Link Layer Security Architecture for Wireless Sensor Networks Chris Karlof :: Naveen Sastry :: David Wagner Presented by Anil Karamchandani 10/01/2007

2. What is ??? Tiny OS Link layer Wireless Sensor Network Tiny Sec

3. 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.

4. 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

5. 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.

6. What is the Difference between WSN and other Network ? WSN Other Networks 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) • 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 .

7. 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

8. 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

9. 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.

10. Design Goals • Security • Access control • Message integrity • Message confidentiality • Performance • Energy • Bandwidth • etc. • Ease of use • MESSAGE AUTHENTICATION CODE • ENCRYPTION • DECREASE MESSAGE LENGTH • PUTIN TinyOS

11. Security Primitive • Message Authentication code • A cryptographic checksum for checking the message integrity • MAC

12. 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)

13. 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.

14. 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 Message Header MAC Message MACs Header

15. 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

16. Different modes of Encryption Symmetric key encryption schemes • A stream Cipher uses a Key and IV . • Together they are ex-ored with message to get the cipher text (C = M+K.IV). • Drawbacks :- If same IV is used to encrypt 2 different packets then there is a possibility of retrieving both the packets. Stream Ciphers Modes of operation using block cipher

17. 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.

18. 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 .

19. 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

20. 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 ??

21. 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

22. Evaluation • Energy Consumption • Power Consumption • Bandwidth - Energy : 24 bytes of data was transmitted

23. Evaluation

24. 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

25. 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 .

27. 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

28. References • http://www.webopedia.com/quick_ref/OSI_Layers.asp • http://camars.kaist.ac.kr/~hyoon/courses/cs710_2004_fall/rhoyo.ppt • http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Cipher-block_chaining_.28CBC.29