I. Introduction
Blockchain technology exploded onto the computer science scene in 2008 when an anonymous user (or users), writing under the pseudonym Satoshi Nakamoto [21], sent to a cryptography mailing list a description of new technology by the name of "Bitcoin". Bitcoin was the first successful decentralized digital asset that is now generally known as a type of cryptocurrency. Popular attributes of cryptocurrencies include the idea that they are completely decentralized and do not rely on a third-person intermediary for transactions which, however, is true for all other conventional currencies.