## 10 Security in WMSN  
Many applications of WMSN have their additional and special requirements in terms of privacy and security, such as military applications, medical care applications, and other video surveillance systems. In addition to the fact that sensor networks are vulnerable to attacks more easily than the wired networks because of their use of a broadcast medium. Therefore, in order to guarantee message authenticity, integrity, and confidentiality, security in WMSN should be taken into account at the design phase of the network, while at the same time maintaining the efficiency and scalability of the network. In order to assure authentication and data integrity for multimedia data delivered over WMSN, an energy-aware adaptive wavelet-based watermarking technique for real time image delivery is presented in [88]. This technique embeds additional data called a watermark into some location in an image object so it can be detected later to make an affirmation about the object. The watermarking locations or positions are adaptively chosen by using two thresholds to insert the watermark according to network conditions so that the energy efficiency and security can be achieved. In order to degrade the effect of the distortion of watermarked image, the proposed scheme embeds the watermark into few positions as possible to make it invisible and allocates extra network resources to protect this embedded watermark from high distortion so it can be detectable. In addition, it also embeds watermark coding redundancies into the original image so the watermark becomes more robust to packet loss. The frequency-based (middle band) discrete wavelet transform (DWT) has been selected because it is more robust, easy to recognizable and authenticated at the receiver side, and it reduces computation complexity and process delay by exploiting the correlation of the inter-frames. In [89], a privacy paradigm called HoLiSTiC is proposed that secures routing and topology information for WMSNs against outsider attacks. The paper assumes a clustered network with some nodes equipped with free-space optical (FSO) capabilities. Also it assumes that the BS and CHs have bidirectional communication links and the camera and transport nodes have unidirectional links. The proposed protocol requires that each node to have an individual key shared with the BS and pairwise keys shared between adjacent visual nodes in a cluster. In addition, every network entity has two pre-deployed network-wide keys. All keys are employed for symmetric cryptography to provide a variety of security services. A secure data converter architecture is proposed in [90] for WMSN that employs fingerprinting and encryption capabilities for simultaneously digitize and authenticate sensor readings. The proposed architecture suggested hardware modifications to the data converter and aims to reduce the computational complexity of the security algorithms at the aggregation points in the systems that need in-network processing. This can be done by embedding an authenticator payload into the data converter or the modulator output in a way that it is not easily extractable without access to the secret key, and can be used to verify the integrity of the sensor reading. New trends in security schemes for WMSNs seem to point to energy-aware and lighter-weight security schemes than for traditional networks. Nevertheless, their nodes can use more processor-consuming algorithms than the ones that would be suitable for Scalar Wireless Sensor Networks. This is so, because at least the nodes that have to process multimedia will have more processing capabilities than the typical scalar node. There have been several papers that propose the use of symmetric cryptography since its lighter processing requirements, but that requires distributed trust by the use of secret sharing or a similar solution, which might be a good solution for some scenarios in scalar WSNs, but not so for WMSNs.