According to one embodiment, an information storage medium comprises a content encrypted by a content encryption key; a content encryption key file encrypted by a first encryption key or third encryption key; an encryption key block from which a third encryption key prime providing a source of the first encryption key or third encryption key by being processed by using a second encryption key of a player; and a program configured to make the player calculate the third encryption key from the third encryption key prime. The content encryption key file comprises a flag indicating whether the key file is encrypted by the third encryption key or first encryption key.