# US 2019/0173858 A1 · Message server, method for operating message server and computer-readable recording medium > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0173858 A1 - Document ID: US20190173858A1 - Status: Published application - Kind: A1 - Application number: 16/269,863 - Filed: 2019-02-07 - Published: 2019-06-06 - Earliest claimed: 2015-10-27 - Assignees: LINE Corporation - Applicants: LINE Corporation - Inventors: Ki Bin SHIN; Jong II Won - Web page: https://patentgrep.com/patent/US20190173858A1 ## CPC - H04L 63/0442: {wherein the sending and receiving network entities apply asymmetric encryption, i.e. different keys for encryption and decryption (cryptographic mechanisms or cryptographic arrangements for public-key encryption H04L9/30)} - H04L 9/0861: {Generation of secret information including derivation or calculation of cryptographic keys or passwords} - H04L 63/0428: {wherein the data content is protected, e.g. by encrypting or encapsulating the payload} - H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)} - H04L 63/08: {for authentication of entities (cryptographic mechanisms or cryptographic arrangements for entity authentication H04L9/32)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract One or more example embodiments include user terminals, methods, and/or computer-readable recording mediums storing computer programs, in which information encrypted or decrypted not to be decoded by a message server that controls transmission and reception of messages between one or more user terminals is not shared with the message server. One or more example embodiments include user terminals, methods, and/or computer-readable recording mediums storing computer programs, which encrypt a first message by using an encryption key, transmit the first message from a first user terminal to a second user terminal, and decrypt a second message received from the second user terminal by using the encryption key. ## Claims ### Claim 1 A message server comprising: a memory configured to store computer-readable instructions; and one or more processors configured to execute the computer-readable instructions, wherein the one or more processors are further configured to: receive, from a first user terminal, a first message including a first attached file encrypted with a first encryption key to transmit, to a second user terminal, a second message including the first attached file encrypted with the first encryption key; in association with the first message, receive, from the first user terminal, first data in which the first encryption key is encrypted with a first asymmetric key associated with the first user terminal and the second user terminal, to transmit the first data to the second user terminal; receive, from the first user terminal, a third message including the first attached file encrypted with the first encryption key to transmit, to a third user terminal, a fourth message including the first attached file encrypted with the first encryption key; and in association with the second message, receive, from the first user terminal, second data in which the first encryption key is encrypted with a second asymmetric key associated with the first user terminal and the third user terminal and transmit the second data to the third user terminal. ### Claim 2 (depends on 1) The message server of claim 1, wherein to receive the first message includes to receive, from the first user terminal, the first message including the first attached file encrypted with the first encryption key that has been randomly generated by the first user terminal. ### Claim 3 (depends on 1) The message server of claim 1, wherein to receive the first message includes to receive, from the first user terminal, the first message including the first attached file that has been encrypted by using a hash value of the first attached file by the first user terminal. ### Claim 4 (depends on 1) The message server of claim 1, wherein the one or more processors are further configured to: when the first message is received from the first user terminal, store the first attached file encrypted with the first encryption key; when the third message is received from the first user terminal, store the first attached file encrypted with the first encryption key; determine whether the first attached file encrypted with the first encryption key is duplicated on the message server; and deduplicate the first attached file encrypted with the first encryption key from the message server. ### Claim 5 (depends on 4) The message server of claim 4, wherein to deduplicate the first attached file includes to deduplicate the first attached file encrypted with the first encryption key from the message server according to a predetermined period. ### Claim 6 (depends on 1) The message server of claim 1, wherein the one or more processors are further configured to: store the first attached file encrypted with the first encryption key on the message server in association with a first index; in response to receiving a request for forwarding the first attached file to a fourth user terminal from the second user terminal, transmit the first attached file encrypted with the first encryption key to the fourth user terminal by using the first index; receive, from the second user terminal, third data in which the first encryption key is encrypted with a third asymmetric key associated with the second user terminal and the fourth user terminal, and transmit the third data to the fourth user terminal. ### Claim 7 (depends on 1) The message server of claim 1, wherein the one or more processors are further configured to: when the first message is received from the first user terminal, determine whether the first attached file encrypted with the first encryption key is existed in the message server; and when the first attached file encrypted with the first encryption key does not exist in the message server, store the first attached file encrypted with the first encryption key. ### Claim 8 A method for operating a message server, the operating method comprising: receiving, from a first user terminal, a first message including a first attached file encrypted with a first encryption key transmitting, to a second user terminal, a second message including the first attached file encrypted with the first encryption key; in association with the first message, receiving, from the first user terminal, first data in which the first encryption key is encrypted with a first asymmetric key associated with the first user terminal and the second user terminal, transmitting the first data to the second user terminal; receiving, from the first user terminal, a third message including the first attached file encrypted with the first encryption key transmitting, to a third user terminal, a fourth message including the first attached file encrypted with the first encryption key; and in association with the second message, receiving, from the first user terminal, second data in which the first encryption key is encrypted with a second asymmetric key associated with the first user terminal and the third user terminal and transmitting the second data to the third user terminal. ### Claim 9 (depends on 8) The method of claim 8, wherein the first message includes the first attached file encrypted with the first encryption key randomly generated by the first user terminal. ### Claim 10 (depends on 8) The method of claim 8, wherein the first message includes the first attached file encrypted by using a hash value of the first attached file. ### Claim 11 (depends on 8) The method of claim 8, further comprising: when the first message is received from the first user terminal, storing the first attached file encrypted with the first encryption key; when the third message is received from the first user terminal, storing the first attached file encrypted with the first encryption key; determining whether the first attached file encrypted with the first encryption key is duplicated on the message server; and deduplicating the first attached file encrypted with the first encryption key from the message server. ### Claim 12 (depends on 11) The method of claim 11, wherein the first attached file encrypted with the first encryption key is deduplicated from the message server according to a predetermined period. ### Claim 13 (depends on 8) The method of claim 8, further comprising: storing the first attached file encrypted with the first encryption key on the message server in association with a first index; transmitting the attached file encrypted with the first encryption key to a fourth user terminal in response to a request for forwarding the first attached file to the fourth user terminal by using the first index from the second user terminal; receiving, from the second user terminal, third data in which the first encryption key is encrypted with a third asymmetric key associated with the second user terminal and the fourth user terminal, and transmitting the third data to the fourth user terminal. ### Claim 14 (depends on 8) The method of claim 8, further comprising: when the first message is received from the first user terminal, determining whether the first attached file encrypted with the first encryption key is existed in the message server; and when the first attached file encrypted with the first encryption key does not exist in the message server, storing the first attached file encrypted with the first encryption key. ### Claim 15 A non-transitory computer-readable recording medium storing computer-readable instructions, the computer-readable instructions comprising: receiving, from a first user terminal, a first message including a first attached file encrypted with a first encryption key transmitting, to a second user terminal, a second message including the first attached file encrypted with the first encryption key; in association with the first message, receiving, from the first user terminal, first data in which the first encryption key is encrypted with a first asymmetric key associated with the first user terminal and the second user terminal, transmitting the first data to the second user terminal; receiving, from the first user terminal, a third message including the first attached file encrypted with the first encryption key transmitting, to a third user terminal, a fourth message including the first attached file encrypted with the first encryption key; and in association with the second message, receiving, from the first user terminal, second data in which the first encryption key is encrypted with a second asymmetric key associated with the first user terminal and the third user terminal and transmitting the second data to the third user terminal.