ISTANBUL — After sharing a prison cell for more than a year, the top executives of Turkey’s oldest newspaper were convicted in April and given heavy sentences for aiding terrorism. But they returned to work last week with determination and a string of jokes.

“In the past I was doing my job smiling,” said Akin Atalay, the chief executive of the newspaper, Cumhuriyet. “Now I am grinning.”

“I have only one problem,” he said, gesturing to Murat Sabuncu, his editor in chief, laughing beside him in the newspaper’s boardroom. “We were together for 24 hours” a day, “and now I don’t want to see him, but I cannot get rid of him.”

Their good humor could hardly disguise the seriousness of the threat against them. For 18 months, the two men have been fighting a group indictment against 18 members of their newspaper, including executives, writers, a cartoonist, accountants and lawyers. Eleven of them were jailed for months in pretrial detention but have slowly been released.