The Bitcoin itself is essentially untraceable if the owner wants to maintain anonymity, and political candidates who accept them must rely largely on donors’ disclosing their identity.

Federal law bans contributions to individual candidates from foreigners, corporations or straw donors, among other restrictions, and campaigns are expected to make their “best efforts” to collect and publicly identify donors who contribute more than $200 in a year and to detect contributions that may be illegal.

“At some level, we are trusting candidates,” said Richard L. Hasen, a campaign finance expert at the University of California, Irvine, School of Law. The system already relies on some measure of trust from candidates, he said, “but the difference with Bitcoin is that it is inherently untraceable.”

In a ruling last year, the Federal Election Commission agreed to allow a political action committee to accept Bitcoins with a voluntary limit of $100, but the commissioners split over how the online currency — which can fluctuate widely in value — should be treated on a broader scale or whether it should be capped.