## 5 Emerging Challenges and Opportunities
### Security and Privacy  
As part of the essential needs for emergency management, sensing data cannot belong solely to individuals. Security and privacy issues thus become more important and challenging.  
_Cyber-world security_: in case of emergencies, wireless mobile devices may need to interact when they encounter each other. Security thus becomes more important than in other cyber-physical systems. Secure pairing of mobile devices [79] allows mobile devices to simply shake (or sense) together, as in earthquakes, so as to construct a common cryptographic key based on data from accelerometers. Such approaches may not always work in emergencies. Instead of authentication by shaking, in [80], two mobile devices are allowed to share data only when they are in proximity of each other. A shared secret key will be generated automatically between the two devices based on their common ambient wireless signals. Mobile devices close to each other will perceive similar fluctuations in wireless signals, whereas they will perceive different fluctuations in wireless signals for devices further away from each other. In this way, mobile devices can authenticate with each other and, thus, secure data exchanges that are freer from malicious attacks (e.g., remote terrorists). As cloud computing boosts many promising services, several efforts focus on the security issue of back-end cloud centres. A conventional way is to encrypt (resp., decrypt) each piece of data before data contributors (resp., consumers) push (resp., pull) the data. In [81], the _user revocation issue_ is discussed; it involves the overheads for key redistribution and data re-encryption when a data contributor wants to revoke some data consumers' access privileges (for example, civilians may revoke pushed data after leaving form emergencies). In this work, each data contributor provides the cloud with a re-encryption key for each valid data customer, where the re-encryption key also helps transform encrypted information between each pair of contributor and consumer. Once a data customer is revoked by a data contributor, the data contributor simply commands the cloud to destroy the re-encryption key so that no overhead is incurred, due to key redistribution and data re-encryption. In practice, multiple types of emergency services (e.g., evacuation in fire events and rescue in earthquakes) may need to collaborate with each other or share resources. Considering the intra-cloud and inter-cloud security, [82] relies on a trusted third-party agreement government to provide all collaborating services with a contract, so as to enable secure communications between multiple services.  
_Physical-world privacy_: as location-based services rely on location information of mobile users, evacuation and rescue applications need even more accurate location information of civilians, raising the issue of privacy. Instead of keeping the detailed locations of mobile users in back-end servers, the approach in [83] pre-fetches location-enhanced content (e.g., a local map) into mobile devices and caches it in advance before it is actually needed. When evacuation and rescue applications require the content, it is retrieved from the cache rather than pushed from the location of civilians with a live query. Due to mobility of civilians, the information can be downloaded and updated at a favorable time (e.g., when WiFi connection is available). Since cloud computing can provide customers with seamless technologies to access distributed database systems (e.g., Amazon SimpleDB [84]), the work in [85] considers separating the user database from service servers for greater privacy. High-privacy data is only stored in the private service server, while the public cloud database stores low-privacy data.