But Mr. Gensler believes that better-known virtual currencies like Ether and Ripple should be in that conversation as well and should likely be categorized as securities, given the way they have been created and sold.

“2018 is going to be a very interesting time,” Mr. Gensler said. “Over 1,000 previously issued initial coin offerings, and over 100 exchanges that offer I.C.O.s, are going to need to sort out how to come into compliance with U.S. securities law.”

The people behind both Ether and Ripple have argued that their tokens are not securities. But there are signs that the S.E.C. could be receptive to Mr. Gensler’s argument. Regulators have indicated in private meetings with industry participants that they are considering whether Ether should be categorized as a security.

All the outstanding Ether were worth around $65 billion at Sunday’s price, while the Ripple tokens in the hands of investors are worth around $35 billion.

If they are deemed to be securities, it could become illegal for Americans to trade them on most of the exchanges where they are now traded. That would make it harder to buy and sell them and depress their prices.

Mr. Gensler developed a reputation for standing up to powerful financial interests when he was the head of the Commodity Futures Trading Commission.