Abstract: In a file sharing system, a key manager unit realizes a correspondence between the first user identifier and the first public key in response to a registration request of the first user, generates a first key material for encrypting the first file into a first encrypted file, and generates a first credential according to the first user identifier, the first file identifier, the first public key and the first key material after receiving an access-right claim request to the first file from the first user. A file storage unit stores the first encrypted file and the first credential. The first user uses the first user identifier, the first file identifier and the first private key to retrieve the first key material out of the first credential, and uses the first key material to decrypt the first encrypted file into the first file.

Abstract: An optical system affixed to an electronic apparatus is provided, including a first optical module, a second optical module, and a third optical module. The first optical module is configured to adjust the moving direction of a first light from a first moving direction to a second moving direction, wherein the first moving direction is not parallel to the second moving direction. The second optical module is configured to receive the first light moving in the second moving direction. The first light reaches the third optical module via the first optical module and the second optical module in sequence. The third optical module includes a first photoelectric converter configured to transform the first light into a first image signal.

Abstract: A method for recovering system status consistently to a designed recovering time point in a distributed database, wherein the distributed database comprises a primary server and multiple region servers, comprising: when the region servers detect a change of system status, analyzing an event for the change to generate an event log and storing the event log to the database; after a preset condition, the region servers generate a snapshot respectively; when the primary server receives the instruction to recover the system status to a designed time point, indicates the region servers to implement: reading the event log and snapshots stored in region servers; finding the snapshot closest to the designed time point; finding the event log and snapshot corresponding to an time interval between the time recorded in the snapshot and the designed time point to recover the system status to the designed time point.

Abstract: A method for recovering system status consistently to a designed recovering time point in a distributed database, wherein the distributed database comprises a primary server and multiple region servers, comprising: when the region servers detect a change of system status, analyzing an event for the change to generate an event log and storing the event log to the database; after a preset condition, the region servers generate a snapshot respectively; when the primary server receives the instruction to recover the system status to a designed time point, indicates the region servers to implement: reading the event log and snapshots stored in region servers; finding the snapshot closest to the designed time point; finding the event log and snapshot corresponding to an time interval between the time recorded in the snapshot and the designed time point to recover the system status to the designed time point.