Whoever they are, the diplomat said, these people need to be reassured that their information, analyses or comments will be treated with discretion, particularly when meant to be passed on to decision makers in foreign capitals. Without that kind of discretion — yes, secrecy — there can be no trust, he said.

“We are entrusted by our governments to be discreet, not to divulge our sources, to stay informed, for the sake of the security of our countries,” said the diplomat. “We are not out there with poison-tipped umbrellas.”

Assessing the damage caused by Private Manning and WikiLeaks is hard to do, said Patrick F. Kennedy, the U.S. under secretary of state for management, in testimony at the Manning trial. “It is impossible to know when someone is not sharing information with you.”

There have been reported cases of people — generals in Zimbabwe, a journalist in Ethiopia, for instance — who have been targeted because of the exposed cables. Contacts in tricky places have become warier, the diplomat said. The fact that newspapers like The New York Times or The Guardian did their best to shield the names of informants is hardly comforting.

“There was a big dump of raw data,” said the diplomat. “I can’t imagine that certain governments restricted themselves to just reading The New York Times version.”

This summer, the Manning case was conflated with the continued pursuit of Edward J. Snowden, wanted by the U.S. government for leaking documents about government surveillance.

The stories are different, but both are essentially about secrets — when governments are entitled to keep theirs, and when they should be allowed access to ours.