Last year, the digital currency market was unstoppable. Having begun the year with a market cap of $17.7 billion, the aggregate value of virtual currencies soared by more than 3,300% to finish 2017 at $613 billion. It was very likely the single greatest year we've ever witnessed for an asset class.There's certainly been no shortage of catalysts that've pushed the market caps of cryptocurrencies higher.For instance, the emergence of blockchain technology is a big reason some investors are so bullish on the virtual currency movement.