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As the wireless sensor networks are easily deployable, the volume of sensor applications has been increased widely in various fields of military and commercial areas. In order to attain security on the data exchanged over the network, a hybrid cryptographic mechanism which includes both symmetric and asymmetric cryptographic functions is used. The public key cryptographic ECC security implementation in this paper performs a matrix mapping of data’s at the points on the elliptical curve, which are further encoded using the private symmetric cipher cryptographic algorithm. This security enhancement with the hybrid mechanism of ECC and symmetric cipher cryptographic scheme achieves efficiency in energy conservation of about 7% and 4% compared to the asymmetric and symmetric cipher security implementations in WSN.

The use of wireless sensor network has been evolved in practise due to the inconvenience of using the wired technology. With the development in network and communication technology, WSN is used in wide areas such as remote sensing, health monitoring, industrial process monitoring, military and various commercial applications. WSN has the ability to balance the harsh environmental conditions, node failures during transmission, scalability of large scale deployment and etc. This network faces the problem of high energy consumption during communication. And various techniques were proposed to conserve energy among the sensors in the network.

Since the sensors are highly involved in data transmission and reception, they pave ways for the attackers to inject suspicious bits into the original message, eaves drop the messages and inhibit various other threat and attacks that affects the confidentiality, integrity and authenticity of the original plaintext [

The data transmission security is commonly achieved through cryptography in WSN. Cryptography secures the data through the encryption and decryption [

The elliptic curve cryptographic technique follows a public key mechanism, which uses different keys for encryption and decryption process [

The authors Hemalatha and Rajamani [

In order to provide a high degree of security for WSN, the author Oreku [

An Elliptic curve cryptography, another public key cryptographic (PKC) algorithm providing same level of security as the RSA but with smaller key size requirements, was used by the author Kodali [

In order to exchange the data among the nodes and the base station in WSN in a secure manner, the authors Kodali and Budwal [

Since the security and excessive power consumption of WSN is becoming the major concerns in recent times, the authors Xu Huang [

Since the ECC security mechanism over the messages can be achieved at the elliptic curve points, this paper follows a new matrix mapping mechanism [

The rest of the section is organized as follows: Section 2 outlines the procedure to process the proposed functions, the results are analysed in Section 3 and finally the Section 4 concludes the proposed work.

In order to ensure security during the data transmission among the sensor nodes in WSN, a public key cryptographic algorithm and a symmetric cipher functions to encode and decode the mapped points on the elliptic curve are used in this paper. Since elliptic curve cryptographic algorithm offers equal security with smaller key size thus reducing the bandwidth and computational complexity compared to RSA, ECC is preferred among all the public key cryptographic techniques.

The following sections explain the procedure to implement the security on the transmitted data over the network.

With the elliptic curve points, operations such as point inverse, point addition, subtraction, and multiplication can be performed. Let a finite field

Where

Mapping can be done in static method and dynamic method [

Let the finite field

STEP 1: The alphanumeric values of each character in the transmitted message should be transferred into their respective ASCII values.

STEP 2: A scalar value that represents the derived ASCII value of the character should undergo a point multiplication with the base point in the elliptic curve. For instance, if x represents a scalar value, then a point multiplication of “x * p” should be performed. This process should be repeated for all the characters in the string.

STEP 3: A “2 × b” matrix “R” should be constructed with the entries of the generated elliptic curve points.

If n is the length of the original message then a = n/2. The space will be represented by the points on the curve that are padded with α.

STEP 4: A 2 × 2 non-singular matrix “S” is chosen as

STEP 5: Finally, the resultant mapped points can be obtained by constructing “U” with the point multiplication and addition process, represented as U = RS + T, resulting in

where,

Once all the alphanumeric characters of the message string are mapped onto the constructed elliptic curve, the mapped points will further be encoded using the symmetric cipher algorithm, which is explained in detail in the next section. The transmitted original message will be retrieved by decoding the message with the symmetric cipher key used to encode the plaintext, followed by the inverted matrix mapping mechanism.

In order to make the message non-readable for the opponent, a symmetric cipher security technique which conserves energy in the WSN is used to encode and decode the mapped message at the point on the curve (

ENCODING

STEP 1: The ASCII value of the alphanumeric character should be generated and their respective binary value should be produced.

STEP 2: Divide the reversed form of the 8 bit binary number generated in step1 with a 4 bit divisor key.

STEP 3: The 8 bit encrypted text should be stored as, the remainder in the first 3 digit and the quotient in the following 5 digit.

DECODING

The encrypted 8 bit cipher text undergoes the below mentioned steps to retrieve the transmitted original message.

STEP 1: The last 5 digit binary value of the encrypted cipher text should undergo a multiplication with the 4 bit symmetric key.

STEP 2: The result obtained in step 1 should be added with the first 3 digits of the encrypted cipher text which forms an 8 bit number.

STEP 3: The transmitted original plaintext can be obtained by reversing the 8 bit digit in step 2.

This section presents a comparative analysis on the energy consumption by the nodes in WSN, among the asymmetric, symmetric and the hybrid cryptographic security implementation. The comparison is done at the intermediate nodes, source nodes, destination nodes and the overall energy consumption in the network.

The experimentation is carried with varying message size of 1024, 2048, 4086 and 8192 bytes on the Atmega 128 16 MHz 8 bit architecture instruction set. The experimentation will start with the basic implementation of sensor network in OPNET Modeler Simulator. Sensor field will be used as logical area with various sensor nodes. We start our proceeding with pre deployment of sensor nodes and continue with implementation of traffic on sensor network. Later the pre-defined asymmetric keys will be distributed to all the sensor nodes. This key distribution will inhibit public encryption to the deployed network. Energy will be measured and must be more than threshold energy level. For the complete segregation of the users, we will use MD5 algorithm at login of the query initiation process which will be processed for ECC encryption further.

cryptographic method is efficient in storage and transmission requirements due to its smaller key size, and the symmetric method is efficient in conserving energy among the sensors during transmission, the entire proposed scheme is found to reduce the energy consumption greatly.

A hybrid cryptographic security mechanism including both symmetric and asymmetric cryptographic techniques is used in this paper to achieve security to maintain the confidentiality, integrity and authenticity of the messages exchanged among the sensors in WSN. The usage of public elliptic cryptography method achieves bandwidth and transmission efficiency due to its smaller key size. The matrix based mapping methodology maps all the alphanumeric characters at the point on the elliptic curve thereby securing the secrecy of the message highly. These

points are finally encoded using the symmetric cipher method. This proposed hybrid security scheme results in the overall energy conservation of about 7% and 4% compared to the individual asymmetric and symmetric cryptosystems in WSN. This work can further be enhanced with factors like lifetime of Sensor nodes, data-block size and transmission range in the network.

S. Hemalatha,V. Rajamani,V. Parthasarathy, (2016) Security Implementation in WSN with Symmetric and Matrix Mapping on Asymmetric ECC Cryptographic Techniques. Circuits and Systems,07,3204-3211. doi: 10.4236/cs.2016.710273