## 1 Introduction  
The Internet of Things (IoT) is an emerging concept that refers to billions of interconnected (non-human) information sources, also denoted as \"smart objects\", typically equipped with sensors or actuators, a tiny microprocessor, a communication interface, and a power source. Existing deployed smart objects typically use proprietary technologies, tailored to one specific application, which results in poor, if any, interoperability and thus limited diffusion on a large scale. Building interconnected and interoperable smart objects requires the adoption of standard communication protocols. International organizations, such as the Internet Engineering Task Force (IETF) and the IPSO Alliance, promote the use of the Internet Protocol (IP) as the standard for interoperability for smart objects. As billions of smart objects are expected to come to life and IPv4 addresses have eventually reached depletion, IPv6 [1] has been identified as a candidate for smart-object communication. The protocol stack that smart objects will implement will try to match classical Internet hosts in order to make it feasible to create the so-called Extended Internet, that is, the aggregation of the Internet with the IoT. Security in the IoT scenarios is a crucial aspect that applies at different levels, ranging from technological issues to more philosophical ones, such as privacy and trust, especially in scenarios like Smart Toys. The security challenges derive from the very nature of smart objects and the use of standard protocols. In [2], the security challenges and requirements for an IP-based IoT are presented by analyzing existing Internet protocols to be applied to IoT and the limitations and problems that such a solution might introduce. In [3], the authors summarize security threats in IoT as follows:  
1. cloning of smart things by untrusted manufacturers;
2. malicious substitution of smart things during installation;
3. firmware replacement attack;
4. extraction of security parameters since smart things may be physically unprotected;
5. eavesdropping attack if the communication channel is not adequately protected;
6. man-in-the-middle attack during key exchange;
7. routing attacks;
8. denial-of-service attacks;
9. privacy threats. Threats 1, 2, 3, and 4 are related to the physical nature of smart objects, which are typically deployed in public areas and cannot be constantly supervised, thus leading to potential damages or counterfeits. Threats 5, 6, 7, and 8 are examples of security issues due to the fact that one has to deal with objects that communicate with each other. Finally, Threat 9 is related to the fact that smart objects might deal with personal or sensible data, which, if intercepted by unauthorized parties, may create ethical and privacy problems. While it is possible to cope with physical nature-related issues only by adopting safe supplying and installation measures, such as avoiding untrusted manufacturers and installers, and by trying to protect smart objects in safe places, all other security threats can be tackled by adopting means, such as secure communication protocols and cryptographic algorithms, in order to enforce the following basic security properties:  
* Confidentiality: transmitted data can be read only by the communication endpoints;* Availability: the communication endpoints can always be reached and cannot be made inaccessible;
* Integrity: received data are not tampered with during transmission; if this does not happen, then any change can be detected;
* Authenticity: data sender can always be verified and data receivers cannot be spoofed. There is an additional property of security that should always be taken into account: authorization. Authorization means that data can be accessed only by those allowed to do so and should be made unavailable to others. This aspect, which requires to identify the communication endpoints, is particularly relevant in those scenarios where it is necessary to ensure that private data cannot be accessed by unknown or unauthorized parties.