  Crypto Currencies have recently gained enormous popularity amongst the
general public. With each passing day, more and more companies are radically
accepting crypto cur-rencies in their payment systems, paving way for an
economic revolution. Currently more than 700 crypto-currencies are avail-able
at Coindesk alone for trade purposes. As of November 2016, the Crypto
currencies hold a total market share of over 14 Billion USD1 [5]. With no
centralized institution to monitor the movement of funds, Crypto currencies and
their users are susceptible to multiple threats. In this paper we present an
effort to explain the functionality of some of the most popular crypto
currencies available in the online market. We present an analysis of the mining
methodologies employed by these currencies to induce new currency into the
market and how they compete with each other to provide fast, decentralized
transactions to the users. We also share, some of the most dangerous attacks
that can be placed on these crypto currencies and how the overall model of the
crypto currencies mitigates these attacks. Towards the end, we will present
taxonomy of the five highly popular crypto currencies and compare their
features.
