## 10 Conclusions and Future Direction  
Trust is one of the key factors in technology adoption, especially in health-related applications. To enhance trust, it is mandatory to safeguard users' privacy and protect users' data from any form of cyber-attack and leaking of information to unauthorised users. In an assistive multimodal robotic system, it is a daunting task to ensure user privacy and protect user data, because there are multiple alternative channels of interaction (e.g., audio, video, gestures) that can be exploited to access personal information. Often, to improve the decision-making process and services of an assistive multimodal robot, smart home sensors and health and wellbeing monitoring systems are integrated and open new channels of multimodal interaction that could be vulnerable. Nevertheless, these alternative channels have minimal or no security mechanisms in place. This is due to their complexity, which makes the application of standard solutions challenging, from both technical and usability points of view.  
This article highlighted some of the main security and privacy challenges of a multimodal assistive robotic system, with the aim of promoting investigation and new solutionsto secure multimodal interactions in assistive robotic systems. We remarked that to improve users' trust, it is important to make the activity and the decision-making process transparent to them. Blockchain, with a resource-aware framework, is envisaged as a potential solution. It was discussed that controlling the assistive robot is a way forward to safeguard users' privacy and avoid data leakage to unauthorised users. It was observed that designing continuous multifactor authentication mechanism is vital, otherwise unauthorised users could easily access services and even extract user's data from the robot. However, the right trade-off between the acceptability and usability of the system must be determined. This trade-off should be related to the type of data and personal preferences. A safe adoption mechanism for remote client connection was also discussed in this article. Moreover, this article highlighted the key cyber-security issues and challenges, and suggested prospective solutions to make assistive multimodal robotic systems adoptable with high confidence among the population. Finally, this article presented and discussed a secure-by-design approach, which could be personalized to achieve an acceptable trade-off between security prompts and usability of the system for the specific user. In future, the proposed security framework solutions will be implemented, tested, and validated with an assistive multimodal robotic system in real scenarios.  
Conceptualisation, J.M. and A.D.N.; methodology, J.M. and A.D.N.; investigation, J.M. and A.D.N.; writing--original draft preparation, J.M. and A.D.N.; writing--review and editing, J.M. and A.D.N.; funding acquisition, A.D.N. All authors have read and agreed to the published version of the manuscript.  
The work of [PERSON] was supported by the European Union under the Horizon 2020 Grant n. 955778 (PERSEO) and by the UK EPSRC with the grant EP/W000741/1 (EMERGENCE).  
Not applicable.  
The authors declare no conflict of interest.