How do you define "currency"? Really anything could be a currency. If my friends (who are they? :) and I wanted to trade with cocoa beans today we could. Would it then be a crime for us to buy cocoa beans from each other using our country's fiat money? One possible way of defining "currency" would involve fiatness, but Bitcoin doesn't have fiatness. It would at least be debatable if such a law would apply to trading back and forth between bitcoins and local fiat money if "currency" isn't nailed down well for the purposes of that law.