## 3 Prototype Description and Implementation
### Security Threat Analysis
This latter subsystem is the one that prevents effective data tampering: once the information is saved onto the network, it is done so with a unique hash number (an output that works as a piece of information characterizing the content of an image) and a timestamp, with both becoming embedded to the data provided. Since the hash number results from applying a hash function to the data, any change on the image or video collected will alter the hash number/output, thus resulting in a hash number/output different from the one that the other participants of the network have, so it will become rapidly evident who the spurious party is. In addition to this, it must be considered that IPFS uses a series of identifiers to guarantee that the data provided neither has been changed, nor the party that first provided it has changed its identification by any means. The IPFS peer identifier ensures that the identification of the node is used to know what user uploaded the files shared with all the other nodes. Additionally, the IPFS hash-based identifiers for the uploaded files provide another unique way of identifying the files in a way that resembles the presented in the blockchain part, so any change in such hash will be noticed by all the other parties sharing that information. 6. UAV hijacking. It could happen that a spurious party gets into the system and manages to alter the UAV normal flight. Since this attack is located at the very end of the system (there is no other subsystem beyond the UAV, nor the UAV connects to any subsystem except for the purpose of taking actions based on the commands that have been received) any security flaw in the wireless interface used to control it or in any previous stage (i.e., credentials to access the CGS got leaked, as it will be mentioned in the next point) can be responsible for the success of this cyberattack. To prevent this, the best action that can be carried out is making use of a secure wireless connection between the CGS and the UAV. In our implementation of the proposed system, this has been done with the built security capabilities provided by the 802.11 ac wireless protocol used for command and data transfer between the CGS and the UAV. CGS credentials exposure. If access to the CGS is obtained by an illegitimate user, they will have complete access to one of the most prominent elements of the system and most of the other security measures will become useless. To prevent this, credentials must be created following several guidelines, which include updating those credentials periodically or making them stronger by applying hash functions or cryptography features on them. Considering all the hardware and software components present in the system, security in this manuscript has been deployed as shown in Figure 9. It can be noted how there are security capabilities at almost every level of communications, as shown below:  
1. The wireless, physical interface is based on 802.11 ac, which provides data encryption capabilities that secure communications when real-time commands are transmitted to the UAV, or images are transmitted from it. 2. At the transport layer, Transport Layer Security (TLS) protocol can be offered as an additional security solution where the transport layer that transfers segments through the network becomes secure as well. Besides, HTTPS requires the usage of TLS for its own functionalities, so its usage is little less than mandatory in this context: with a TLS certificate, HTTPS can encrypt web requests and responses (which becomes especially useful when requesting information to the IPFS network) that can be digitally signed. 3. Security protocols provided at the application level before reaching the IPFS network has also been offered by means of using HTTP Secure (HTTPS) as the application layer protocol, which will enable further securitization of communications when working combined with TLS. 4.