I think you might have a hard time at this finding an attack that is worthy of a Master's Thesis.   For this I think you would need to find your own attack or at least your own variant, and sounds like a very hard to do.    It might be possible... but I would look at other options then an attack.

Before you get to far in this have you thought about instead of an attack looking at using a study of "Blockchain".  It is kinda all the rage to use "Blockchain" technology when someone launches something that want's investors anymore.   It is something if you had a good thesis in you might be able to use to help get a job.   I think a thesis in "Blockchain" is going to be much more achievable on a master's level then a attack unless you are very talented at finding exploits.