Homework 3 in Bitcoin course
https://gist.github.com/debanshu/eab9ccf8376eb2ce270638610329fabf
This assignment have a little bit different from the original
This provide RSA API instead of Crypo Class in the original
https://github.com/msilb/coursera-cryptocurrency/blob/master/assignment-1-scroogecoin/TxHandler.java