**1. Introduction**

In the past decades, wireless Sensor Networks (WSNs) attracted many researchers. A lot of them considered important issues such as: routing, security, power awareness and data abstraction, But security is prior common assumption in the most of works. On the other hand, WSNs should collect small size and especially secure data in real-time manner. This problem is considered because sensor nodes are small, low power with low storage. Therefore, classical algorithms maybe inapplicable, i.e. considering constrained sensor, these algorithms cannot guarantee the security of data. The aforementioned problem is very critical in the new generation of WSNs referred to as Unattended or disconnected wireless sensor networks.

The disconnected networks are established in critical or military environments. Hence, sink or collector is unable to gather data in real-time manner. Moreover, the network will be leaved unattended and will be periodically visited. This property provides some threats such as discovering and compromising sensor nodes by adversary without detection. Moreover, adversary invisibly performs to be intractable and unpredictable. Also, some adversary is curious and aims just to disclose data, while some aims search data to replace them with forged. The third kind of network adversary whiles to inject invalid data to corrupt network called DoS attack or mislead sink. In such setting, the main challenge is assurance about data survival for long time.

In this research, we propose scheme that firstly shares generated data and encodes them to provide confidentiality and integrity. Moreover, utilizing efficient mathematical solution, every sensor with unique identification encodes shares, in which encoding process is oneway with initial boundary conditions. Then a linear signing algorithm applies to provide authentication and prevent DoS attack. In addition, in order to defend curious adversary, the signed generated data will be broadcasted to the neighbour sensors. Every neighbour uses network-encoding for received shares and homomorphic signs to remove previous signature and generate unique signature. This process decrease size of total received shares.

*Organization:* Section 2 reviews the related work of UWSNs. Section 3 sketches our proposed algorithm including applied network coding, homomorphic and mathematical solution. In section 4 we have demonstrated our scheme efficiency implemented by Maple. We have ended this chapter with conclusion section.

Linearly Time Efficiency in Unattended Wireless Sensor Networks 215

**Energy (mJ)**

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[2] In order to implement and evaluate some key operations for re-encryption process, the code of the MIRACL library [3] is adapted. They measure inversion and exponentiation operations through the polynomial arithmetic which depend on the field chosen. The algorithm used for inversion is a polynomial version of the Extended Euclidian algorithm from Lim and Hwang [4]. They have chosen a general algorithm for exponentiation. Although the symmetric algorithms are not expensive, the re-encryption strategy is still the main alternative against proactive adversaries. Moreover, according to [2], the Elliptic Curve Cryptography (ECC) schemes show an important drawback of the re-encryption solutions,since the exponentiation is not as suitable as polynomial operations. Hence Public

Ren et al. [5] prove that in order to achieve perfect security, data sharing between neighbours is suitable way. Therefore, in our scheme, sensor node collects data *data* and breaks it to equal shares *d1, d2…, dn*. Using following process, the sensor sends signed

After sensor *vi* collects data *data*, it proceeds following steps to achieve data integrity,

2. Using our mathematical encoding solution (refer to section 3.5), the sensor encodes

*i* to the each neighbour.

δ*i*).

δ

**3.1 Share generation, encoding, signing and broadcasting processes** 

Fig. 1. Time costs for super-encryption (100 executions)

Key Cryptography (PKC) should be considered.

encoded *Yi* to the randomly selected neighbours.

confidentiality and also authenticity. 1. Shares *data* into equal *d1,d2,…,dn*.

3. Every *Yi* will be signed by sensor *vi*(

4. Lastly, sensor *vi* broadcasts every

**3. Proposed scheme**

every *di* to *Yi*.

Table 1. Super-encryption energy consumption (100 executions)
