there are some university in NEw york which have started masters degree. and there is a university in Cyprus which provides an online masters for crypto currency. they are providing the introduction course for free irrespective you enrol in masters or not.
You can research on algorithms they use and take up the subject as your phd program. there is a indian origin professor in a university in USA(i dont rememebr which) but you can find his details from a term paper writing service course he is providing in coursera. You can contact him and find out if he can admit you as his student for phd. if they dont allow crypto currency as a subject, you can take the underlying topics in crypto like cloud encryptions(used for online wallets) etc. The Massachusetts Institute of Technology, New York University and Cornell University are the top three universities that offer courses and majors in blockchain technology (New York University was the first one to do that last year). But Curtin University is now one of the most discussed Australian universities, cause it has created a PhD scholarship program which is funded by cryptocurrency. Coursera and edX give the basics, but it's not enough to write an academic research. I chose Stern School of Business (New York University) and I'm glad I made that choice.