上周摩根大通的首席執行官痛斥比特幣為“騙局”，“比荷蘭郁金香泡沫還惡劣。”如果你同意他的說法，可能會想到做空。摩根大通高管抨擊以后，比特幣交易價確實出現下挫，雖然價格較今年1月仍漲了四倍（本周二價格為每個3850美元）。沒準，做空比特幣的機會真來了。

怎樣才能做空全球人氣最高的數字貨幣——比特幣？由于（和其他資產相比）比特幣相關的金融產品比較少，而且某些手段只有專業投資者才會操作，普通人想做空并不容易。不過采用以下五種方法還是可以實現的。

1）通過保證金交易買入比特幣，然后拋售

通過Coinbase旗下的GDAX之類比特幣交易平臺，用戶可以通過保證金買入。雖然保證金買入交易通常用于加杠桿做多某項資產，但也可以通過保證金賣出比特幣，之后再平倉。如果比特幣價格在交易期間下跌，就可以獲利。

用這種方法需要注意幾點。一是GDAX要求，如果美國公民希望利用保證金交易，其個人可支配投資金額至少得有500萬美元（總部位于舊金山的交易平臺Kraken看來并沒有相關限制）。二是保證金交易的持倉時間相對較短，比如GDAX允許持倉最多27天。這意味著，做空客戶賭的是比特幣短期內會下跌，否則將不得不回補空單，彌補比特幣漲價的損失。

2）做空比特幣ETF

今年美國證券交易委員會拒絕了雙胞胎文克萊沃斯兄弟推出比特幣交易所交易基金（ETF）的請求。若這一申請獲批，該ETF的股份就可以在大型交易所交易，普通投資者能像做空普通的個股一樣，通過個人投資賬戶做空比特幣ETF。

SEC正在重新考慮之前的決定。在此期間，唯一一個類似股票可供做空的選擇是ETF Bitcoin Investment Trust。顧名思義，Bitcoin Investment Trust是一只對標比特幣的信托基金，交易代碼為GBTC，投資者可以買賣份額。

這種方法也有要注意的事項。一是GBTC還沒能登陸大交易所，只能在場外交易市場（OTC）（所謂“粉單”市場）交易，和尚未滿足上市標準的證券一樣買賣。投資者通過TD Ameritrade之類大經紀商可以購買OTC交易的證券，但不能做空，所以做空GBTC難度更大。最后要指出，GBTC的交易價已經和比特幣價格（基本上GBTC已經變成單純的投資工具）脫鉤，所以做空GBTC并不完全等于做空比特幣。

3）在期權交易所LedgerX購買比特幣的衍生品（實際推出后）

經驗豐富的投資者可能希望借道期權和其他衍生品做空比特幣，尤其是買入“看跌期權”，日后以當前的高價賣出比特幣。如果比特幣交易價開始下跌，看跌期權就會增值，持有者就可以獲利。

目前市面上還沒有這種衍生品合約，但應該很快問世。今年7月，一家名叫LedgerX的公司獲得美國商品期貨交易委員會（CFTC）批準成立清算所，處理虛擬數字貨幣看跌和看漲期權、掉期合約和其他各類衍生品合約的交易和清算。預計LedgerX很快就會開展業務。

（更新：位于香港的Bitmex一直是處理比特幣相關衍生品交易的平臺。要注意的是，該平臺的所有交易都通過比特幣進行，包括計算盈虧，所以在做空比特幣以前必須先買入比特幣。）

4）請高盛幫你做空

這種方法不太適合一般投資者，我是在咨詢一些很有錢的風投基金時聽說的。最近有一次吃晚飯時我問風投大佬們，既沒有衍生品也沒有其他常用的交易手段時怎樣做空比特幣。

他們的答案是，高盛之類投行可以幫你交易空單，做空任何標的。（大家還記得電影《大空頭》的主人公請銀行幫忙做空美國房產市場嗎？）因此，如果相信比特幣是個泡沫，也許可以定制合約押注比特幣崩盤。

5）做空追蹤比特幣價格的個股

風險資本家、數字貨幣興起之初的投資者尼克希爾·卡爾加特基認為，加密數字貨幣市場如今發展遇阻，因為大玩家缺少進行對沖的策略。對此他提出了一種做空比特幣的方法：挑選一些追隨比特幣價格而動的個股建立投資組合，然后逐個做空。但卡爾加特基也承認將相關股票挑出來不太容易。

卡爾加特基不是唯一一個提出這種方式的。英國《金融時代》的博客Alphaville最近將芯片制造商英偉達列為做空比特幣的標的，因為英偉達的產品在挖礦加密數字貨幣的行當中十分受歡迎。然而英偉達還有其他領域的產品，簡單將其當成比特幣龍頭股有點簡單粗暴。

歸根結底，普通投資者想做空比特幣的話現在還沒什么簡單的方法。如果堅定看空，自然能找到做空的方法。如果沒那么篤定，或許要等到比特幣ETF或者衍生品上市再做打算了。（財富中文網）

譯者：Pessy

審稿：夏林

The CEO of J.P. Morgan this week called bitcoin a "fraud" and "worse than tulip bulbs." If you agree, it may be tempting to bet against the digital currency. Sure, the price has taken a beating of late but it's still up 400% from January ($3,850 as of Thursday) —offering an opportunity for bitcoin bears.

So how exactly do you short bitcoin? It's not easy due to a lack of financial products (relative to other assets) and because some tactics are restricted to professional investors. That said, here are five approaches for bears to bet against the world's most popular digital currency.

1) Buy it on margin and then sell it

Trading platforms like Coinbase-owned GDAX allow you to buy on margin. While margin purchases typically involve adding leverage to go long on an asset, it's also possible to go short by selling bitcoins on margin, and then closing out the position later on. If the price of bitcoins drops during this time, you'll profit on the trade.

There are a couple caveats. One is that GDAX requires U.S. residents to have at least $5 million if they want to trade on margin. (San Francisco-based rival Kraken doesn't appear to have this restriction). The other is that customers can only leave margin positions open for a relatively short period of time—27 days in the case of GDAX—which means those betting on a fall in bitcoin need it to tumble in short order, or else they will have to cover the price increase.

2) Short shares of the Bitcoin Investment Trust

The SEC this year rejected an application by the Winkelvoss twins to launch a bitcoin ETF. The shares of the ETF would have traded on a major exchange, and let ordinary investors use their brokerage accounts to short them in the same way as an ordinary stock.

The SEC is reconsidering the decision but, in the meantime, the only stock-like alternative is the Bitcoin Investment Trust. As its name suggests, this is a trust that holds bitcoin and lets people trade its shares under the ticker GBTC.

Once again, there are catches. One is that GBTC is not eligible to trade on major exchanges, so instead it's listed on OTC Markets (aka the "pink sheets") alongside other misfit toys of the equities world. Big brokerages like TD Ameritrade do let investors buy OTC-listed stocks—but not short them, which makes it harder to bet against GBTC. Finally, the price of Bitcoin Trust shares have become untethered to the price of bitcoin (it's basically broken as an investment vehicle) so a short bet is not exactly a bet on bitcoin itself.

3) Buy derivatives on LedgerX (when they arrive)

Experienced investors may wish to wade into the world of options and other derivatives as a way to be bearish on bitcoin. Specifically, they could buy a "put option" to sell bitcoin at its current high-flying price. If the price of bitcoin starts dropping, the option will increase in value and its owner can pocket a profit.

These derivative contracts are not available yet, but they should be soon. In July, the Commodity Futures Trading Commission approved a bid by a firm called LedgerX to open a clearinghouse for crypto-currency puts, calls, swaps and all sorts of other exotic contracts. LedgerX is expected to be open for business in the near future.

(Update: There's also Hong Kong-based Bitmex, which is a long-time purveyor of bitcoin-related derivatives. One catch: all transactions, as well as profits and losses, are conducted in bitcoin—meaning you must buy bitcoin before you can short it).

4) Ask Goldman Sachs to write you a contract

This approach is admittedly not for Joe Blow investors. It came up when I asked a few wealthy VCs at a recent dinner how they would short bitcoin given the current absence of derivatives and other common trading strategies.

Their answer was that investment banks like Goldman will write you a short position on anything you like. (Remember that scene in The Big Short when the protagonists ask banks to help them short the U.S. housing market?). So someone who believes bitcoin is a bubble could create a bespoke contract to bet on just that outcome.

5) Pick stocks that track bitcoin prices—and short them

Nikhil Kalghatgi, a venture capitalist and early digital currency investor, believes the cryptocurrency market is hindered right now by a shortage of ways for big investors to deploy hedging strategies. In response, he suggests one way to bet against bitcoin is to create a basket of stocks that move with the price of bitcoin and short them accordingly. Alas, Kalghatgi says he is not confident enough to pick what those stocks would be.

He's not the only one to propose this idea. The Financial Times'Alphavilleblog recently singled out shares of the chip maker Nvidia, whose products are hugely popular with cryptocurrency miners, as a potential proxy for those looking to short bitcoin. But Nvidia makes products for all sorts of other industries, so using it as a bellwether for bitcoin would be a crude metric.

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The bottom line is that, for now at least, there is no simple way for ordinary investors to short bitcoin. Determined bears can and will find ways to do so—but everyone else might want to hold out for a bitcoin ETF or derivatives to arrive.