Choosing a topic for a PhD dissertation?

Question

Internet of Things

Good afternoon! Not long ago I entered graduate school (the form of an applicant).
The question arose about choosing a topic in the specialty methods and means of protecting information, information security.
Picked up a few topics forgive to give their advice.
1. The problem of information security in IoT devices.
2. Methods and models for protecting information in the industrial Internet of things using machine learning.
Keywords: IoT, IIoT, Machine Learning, Azure, CyberSecurity, Security.

Answer 1

Topic: "The ability to build a network of distributed computing based on IoT devices."
Roughly speaking, will Skynet (or some kind of hacker) be able to make a supercomputer out of kettles, refrigerators and TVs.