Cameron and Tyler Winklevoss, whose legal feud with Facebook was famously depicted in the movie The Social Network, are bullish on Bitcoin.

A few months ago, shortly after a major Bitcoin price spike, the twins revealed they owned about one percent of all Bitcoins in circulation. Such an investment was worth, at that time, around $11 million.

"We have elected to put our money and faith in a mathematical framework that is free of politics and human error," Tyler Winklevoss said at the time.

Now they're launching a venture meant to make it easy for the everyman investor to get a piece of the Bitcoin action. The Winklevosses have filed paperwork with the Securities and Exchange Commission revealing plans to sell $20 million of public stock in the Winklevoss Bitcoin Trust, an exchange-traded fund in which owning stock corresponds to owning a certain amount of Bitcoins.

On the first day of trading, one million shares will be sold, with each one expected to correspond to about 0.2 Bitcoins. Overall, shares in the Winklevoss Bitcoin Trust will track to a weighted average of Bitcoin prices, which they call the Blended Bitcoin Trust.

In their S-1 filing, the twins list all kinds of risk factors that investors may want to consider. Some of them state what's obvious to anyone following Bitcoin news: the currency is volatile, for instance. Others are more far-out possibilities that are nonetheless interesting to consider: Miners could become discouraged, the Bitcoin Network could be hacked into by a botnet, or the open-source Bitcoin software could be "forked" into a separate network, the Winklevoss Trust notes. Any of those developments could damage the value of Bitcoins or what they call "Digital Math-Based Assets." If the company goes public as planned, it would be the first Bitcoin-centric IPO in US markets.

This announcement comes at a time when the chief Bitcoin exchange, Mt. Gox, is under investigation by US federal law enforcement and has had some of its assets seized. Late last week, Mt. Gox finally registered with FinCEN, the US Treasury Department's anti-money-laundering regulator.