Idling away the hours in a darkened room in Gaza with two other hostages, Andrey Kozlov sometimes heard one of his captors on the other side of the door typing away on a laptop.

The man was a constant presence in the apartment, while other guards worked shifts and went out to the market, Mr. Kozlov said in an interview, from a hotel room in a Tel Aviv suburb a month after his rescue from captivity.

The guards were unmasked, but they were careful not to reveal their names, telling the hostages to call them all Muhammad.

To differentiate between them, Mr. Kozlov said the hostages gave them nicknames like Big Muhammad and Little Muhammad. Their main jailer had a rounded face, so they called him “Muhammad H’dudim,” Hebrew slang for “Muhammad Chubby Cheeks.”

Mr. Kozlov, 27, a Russian Israeli, provided an exceptionally detailed account of his total of eight months in captivity, together with Almog Meir Jan, 22, and Shlomi Ziv, 41.

He described being held in six locations in the first two months, finally moving to the apartment in mid-December. In some places, he and the other hostages had only a pail for a toilet and food was scarce. Mr. Kozlov said he lost about 20 pounds.