# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 3 BBN Design Considerations
### Security Policies for BBN  
Given their restricted resources, especially in terms of energy supply, often body sensors are vulnerable to data injection attacks, that aim to consume the resources of a target WBAN by flooding its nodes with false data. Especially, when a WBAN roams from one BBN to another, a handover mechanism takes place increasing the risk of the physical capture of the WBAN. Thus, mostly invasive attacks happen during the mobility of WBANs beyond the BBN borders or APs' coverage zone. Yet, issues related to security must be investigated in BBNs, and security schemes should be designed in accordance with the intended applications and their possible threats. In a U-healthcare context, holistic security scheme is, above all, a mandatory requirement for U-health BBN application design, since human lives are definitely at stake. Privacy measures, as well as intrusion detection mechanisms, are mandatory in such networks. Therefore, through the implementation of tough data encryption and constant network monitoring, WBANs could preserve their own privacy. Very few works investigate the security issue in BBNs, such as [73], where a chaotic compressive sensing (CCS) is implemented to solve three major issues in BBNs: storage space, energy saving and data security. Chaotic compression is intended, specially, to encrypt images, as it is a highly recommended function of BBNs, in order to report real-time situations in remote healthcare, rescue or military applications. In [74] the authors proposed a hybrid security solution based on preloaded keys and biometric-generated keys. It provides an efficient solution for intra-WBAN and inter-WBAN communications:* Intra-WBAN: the sensors measure physiological values (PVs) of the human body and then the keys are generated using those PVs to secure communications. * Inter-WBAN: preloaded keys are used. The technique is memory-saving since it combines auto-generation and preloading key to enhance security. Any personal server (PS) can use biometric information to generate a key pool that it shares to the WBANs. The medical server (MS) assigns the responsibility of refreshing the key to any PS generator. This hybrid solution averts from different attacks like outsider attack, PS compromise, sensor node compromise, etc., and ensures the confidentiality, authentication and integrity of WBAN communications. Such a solution could be useful for a BBN scenario, since it considers the inter-WBAN communications, which include the communication among the PSs to deal with situations when a PS is out of range of the MS. However, this hybrid security mechanism does not consider dynamic scenarios where WBANs are mobile and, thus, could encounter further security threats, due to their position changes. Yet, authors of [75] proposed a cluster-based security mechanism for intra and inter-WBAN communications in a healthcare context. It takes into consideration the mobility of WBANs to the extent that it implements a WBAN neighborhood discovery mechanism, re-clustering in case of cluster head leaving or new arrival WBAN configuration, and WBAN addition or eviction. The proposed security mechanism consists of an energy-efficient key management scheme for WBANs that monitors the energy level of the node during the key management process. This framework supports both intra and inter-WBAN security and is then highly recommended for BBNs. On the other hand, authors in [76] proposed a new method to improve WBAN security by decreasing the required memory, control packets complexity, control buffers and mend the existing damages resulting from the high speed of transferring data between nodes. To ensure these goals, ref [76] proposes a cryptography scheme to secure the intra-WBANs communications, by combining the advanced encryption standard (AES) and sensor node bio-signals. Besides, there are several security proposals in the literature for WBANs and their applications, the work in [77] reviews some of them.