1. Efficient aggregation of encrypted data in Wireless Sensor Network Author: Einar Mykletun, Gene Tsudik Presented by Yi Cheng Lin Date: March 13, 2007

2. Outline Introduction Conditions Additive Homomorphic Encryption Aggregation Result Conclusion

3. Introduction Security in Wireless sensor networks (WSNs) is a popular research topic in recent years Aggregation techniques are used to reduce the amount of data communicated within a WSN and thus conserves battery power This paper blend inexpensive encryption techniques with simple aggregation methods to achieve very efficient aggregation of encryption data

4. Conditions(1/2) Multi-level network tree (3-ary) Additive homomorphic encryption M: message space C: ciphertext space M is a group under operation C is a group under operation c1 = Enc k1 (m1), c2 = Enc k 2 (m2)

5. Conditions(2/2) Computing the average and variance The packet header is 56 bits End-to-end aggregation in WSNs Compare to hop-by-hop (HBH) and No-Agg

6. Additive Homomorphic Encryption

7. n different ciphers c i M >= >= with t = max(m i ) The key stream k can be generated by using a stream cipher, such as RC4 t

8. Aggregation Computing the Average  c xi = Enc(x i, k i, M), M = n*t, log(M)=log(n)+log(t)  C x =  S x = Dec(C x, K, M) = C x – K (mod M), where K =  Avg = S x /n Computing the Variance  y i = x i 2, c yi = Enc(y i, k i ’, M’), M’ = n*t 2, log(M’)=2*log(n)+log(t)  C y =  V x = Dec(C y, K’, M) = C y – K’ (mod M), where K’ =  Variance = V x /n – Avg 2

9. Result

10. Conclusion(1/2) This scheme is slightly less bandwidth efficient than the hop-by-hop aggregation scheme However it provides a much stronger level of security One limitation of this proposal is that the identities of the on-responding nodes need to be sent along with the aggregate to the sink

11. Conclusion(2/2) Reduce n (number of nodes) or t (value)