## 2 Security on LoWPAN Networks  
Note that both LoWPAN networks and general resource unconstrained networks share almost the same security requirements [12, 16]. However, due to the node resource constraints, the number of nodes and the absence of an organized communication infrastructure, supporting security services in LoWPAN networks is more challenging when compared with resource unconstrained networks. Confidentiality, authenticity, integrity, availability, data freshness, robustness, and survivability are the most relevant security requirements in LoWPAN networks [17, 18]. Confidentiality ensures that only legitimate entities have access to the data transmitted and stored in the network nodes. Authenticity ensures that data is actually provided by its source nodes. Integrity guarantees that no data is changedby any other entity, without being detected. Availability ensures that services provision is always available to their legitimate users. Data freshness prevents other entities from replaying old messages. Network robustness and survivability guarantees that the network still works properly even in the presence of intrusions, attacks, accidents and failures. Following [19], LoWPAN security attacks can be broadly classified as external _versus_ internal attacks, passive _versus_ active attacks and more-class _versus_ laptop-class attacks. In external attacks, the attacker device can only use its own resources to perform the attack and has no access to the resources of the other LoWPAN nodes. External attacks can be prevented with cryptography. For example, a cryptographic mechanism used to support authentication and confidentiality prevents an external attacker from eavesdropping third-party messages or injecting false messages. In internal attacks, the attacker device is able to compromise legitimate nodes by using their resources to perform the attacks. Internal attacks involve either the injection of malicious code into target nodes (exploiting flaws in the application modules) and/or the access of key material code and data of the target nodes. This type of attack enables the attacker to appear as a legitimate node in the network gaining the trust of the other legitimate nodes. Internal attacks are much harder to detect when compared with external attacks [20]. Passive attacks are based on information gathering without modification. Eavesdropping and monitoring are examples of passive attacks. The active attacks involve modifications on the legitimate data stream or false data injection. In the more-class attacks, nodes with similar resources as the legitimate nodes are used to perform the attack. In laptop-class attacks, an attacker uses devices with more resources, such as laptops, to perform the attack. Laptop-class attacks are especially effective, for example, to jam the wireless channel. Security attacks against LoWPAN networks can also be classified, according to security requirements, in the following three main groups [16]: attacks against secrecy and authenticity, attacks against network availability, and stealthy attacks (_i.e._, attacks against service integrity). Eavesdropping, packet replay, tampering and spoofing are examples of attacks against the secrecy and authenticity. Denial of service (DoS) is the main example of an attack against the network availability and can be targeted at the different layers of the networking stack [9, 10]. In the stealthy attacks, the main goal is to make a legitimate node to accept false data values generated by the attacker and, in this way, the compromised legitimate node can also be used to amplify the dissemination of false data through all other legitimate nodes. Several mechanisms, most of them based on cryptography, can be used to address these different requirements in LoWPAN networks. Currently, the research on providing security solutions for LoWPAN networks has been focused mainly in three categories: (i) key management, (ii) authentication and secure routing and (iii) secure services.