Protection from Unauthorized Replacement. As the storage capacity is limited, a replacement process must be carried out when the capacity exceeds its limit. It means the situation that a currently stored content must be removed from the storage space in order to make space for the new coming content. However, how to decide which content should be removed is very important. If an unauthorized replacement happens, the content which the user doesn‘t want to delete will be removed resulting in an accident of the data loss. Furthermore, if the important content such as system data is removed by unauthorized replacement, the result will be more serious.
