Method and apparatus for de-duplicating encrypted file through verification of file possession, and method and apparatus for storing encrypted file

A method for storing an encrypted file in a server by a client, comprising:

• transmitting a first client identifier of the client and a first encrypted file identifier for a first encrypted file to the server;
• receiving a random number from the server, when the first encrypted file identifier is present in the server;
• hashing the random number and the first encrypted file to generate a first verification value;
• and
• transmitting the first verification value to the server.

A server comprising:

• a first database;
• and
• a processor searching a first encrypted file identifier in the first database when the first encrypted file identifier is received from a client,
• wherein the processor transmits a random number to the client and hashes a first encrypted file corresponding to the first encrypted file identifier among encrypted files stored in a second database and the random number to generate a first verification value, when the first encrypted file identifier is searched, and
• the processor compares the first verification value and a second verification value based on the random number with each other to confirm whether or not the client possesses the first encrypted file, when the second verification value is received from the client.