Former Federal Reserve chairman Ben Bernanke spoke about crypto in an interview with CNBC, noting that as a substitute for fiat money, which they were intended to be, cryptocurrencies haven’t succeeded, but as a speculative asset they are successful.

Bernanke, who served as the Fed chairman from 2006 to 2014, believes the main use of bitcoin is mostly for underground economic activities and often things that are illegal or illicit, and doesn’t expect it to take over as an alternative form of money.