They can be regulated by proxy by licensing and taxing miners' electrical consumption, and crypto exchanges that transmit fiat. But bitcoin, ether, litecoin and most other protocols (although not Ripple's XRP, which is a true token created administratively) just hash data using known algorithms (such as SHA-256). Use of such algorithms cannot be restricted in nations with any kind of rule of law. (Only poverty can do that, such as is found in Cuba and N. Korea.) Nor can the digital products of such algorithms (bitcoins, ethers, litecoins) be banned for the purposes of commerce. Not being fiat, to use such products to obtain goods and services is to engage in literal trade, or barter. The only regulatory potential there relates to tax enforcement, not suppression.