## 3 Background Study of Assistive Multimodal Robots
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Requirements** & **Motivation** & **Current State** & **Possible Solution** \\ \hline \multirow{8}{*}{Transparency} & \multirow{8}{*}{User would know what, why, and when actions are taken by the robot.} & No known blockchain solutions exist for a multimodal robotic system, but a detailed survey about blockchain solutions in robotics is highlighted in [55]. There are lots of blockchain solutions in different applications, as provided by different authors in [49; 50; 51; 57; 59; 60; 61]. It could also be applied for a security solution in a multimodal robotic system. & A private blockchain with permission based access control mechanism is a potential solution. So that only authorised users can access the data, but it would be designed in such a way that the consensus technique and storage does not affect the blockchain network performance. The design would consider the block storage mechanism, data transmission update, and validation process and participation of nodes during consensus to improve efficiency and reduce overheads. & The threat model differs depending on the environment, presence of users, local or remote access, and the presence of intruders or unauthorised users. Therefore, secure frameworks would be develeoped in such a way that the robot communicates with the users if and only if the user’s privacy is protected and the environment is safe and channel secure. & User and assistive robot communication should be secured. However, it would be impossible to secure all the channels, e.g., the verbal conversation, signals, and signs in presence of other users. Therefore, the robot should know what to do and what to say and when to say it, or when to provide the service (in other words teaching the robot to behave in such scenario may be the best solution to secure data and preserve user’s privacy). If technology is used to communicate with assistive multimodal robots then this can be secured easily using any standard encryption techniques, but the method used should not degrade the robot’s performance and response time. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Security and Privacy Requirements and Prospective Solution Directions [46; 49; 50; 51; 55; 56; 57; 58; 59; 60; 61]. \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Requirements** & **Motivation** & **Current State** & **Possible Solution** \\ \hline \multirow{9}{*}{Data Integrity and Avalability} & \multirow{5}{*}{To avoid non-repudiation and tampering. Detect and protect from attacks to increase data availability etc.} & Secure standard hashing algorithms should be used like SHA2, SHA3 etc. Because hashing like SHA0, MD4, MD5 are no longer secure, so it should be avoided [56], even SHA1 is no longer secure, since hash collision attack was found by Google ([[https://security.googleblog.com/2017/02/announcing-first-shal-collision.html](https://security.googleblog.com/2017/02/announcing-first-shal-collision.html)]([https://security.googleblog.com/2017/02/announcing-first-shal-collision.html](https://security.googleblog.com/2017/02/announcing-first-shal-collision.html)), accessed on January 22) recently. Authors of [58] conduct a systematic review paper on robotic attacks, counter-measures and recommendations but not related to multimodal security system. & No new mechnsisms for data integrity would be developed, but the most effective mechanisms would be explored and incorporated in a blockchain solution. A novel approach of an efficient integrity detecting technique would be developed within a merkle tree of a blockchain system, so that any attempt at tampering is self-healing within a node. This would avoid invoking other nodes or devices for approval or concensus when changes within a block take place after it is created and validated. This approach would revert any changes safely to the original state of the block.