Open Encryption.

To encrypt the memory card without saving the key, select Memory card > Encrypt without saving key. If you select this option, you cannot use the memory card in other devices, and, if you restore factory settings, you cannot decrypt the memory card.

To encrypt the memory card with a key you have received, select Memory card > Encrypt with restored key.

To encrypt the memory card and save the key manually in the default folder, select Memory card > Encrypt and save key. For security, store the key to a safe place outside the device. For example, you can send the key to your computer.