SAN FRANCISCO—Barton Gellman, one of the few journalists that has been given access to the entire trove of documents provided by whistleblower Edward Snowden, told the RightsCon conference Tuesday that American federal authorities have declined to provide him with a secure means to communicate with them.

Gellman told the assembled crowd that he had never before revealed this information in public.

“There's a peculiar thing: [intelligence agencies and I] do have conversations about stories that I'm going to publish,” he said. “I want to know context and I want to authenticate information or not be radically out of context. And sometimes they want to make a case to me about something that I don't know that would make a difference on what to publish. So I’ve said to them: 'How would you like to communicate other than open e-mail or telephone?' And they've yet to give me a secure channel—which I find surprising.”

Gellman explained that the government has set up a self-imposed classified trap, where officials are not allowed to discuss classified materials on nonclassified channels. They also can’t discuss declassified materials over open networks.

“It seems to me that they could solve this problem and ought to,” he said.

Last week, Gellman told another conference at Georgetown University that he had been informed that his phone records had been subject to a National Security Letter.

Gellman's book, Angler: The Shadow Presidency of Dick Cheney, was the only book that Snowden took with him when he fled from Hawaii to Hong Kong in June 2013.