# US 2013/0159696 A1 · Sending messages by oblivious transfer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0159696 A1 - Document ID: US20130159696A1 - Status: Published application - Kind: A1 - Application number: 13/706,672 - Filed: 2012-12-06 - Published: 2013-06-20 - Earliest claimed: 2011-12-16 - Assignees: International Business Machines Corporation - Inventors: Takaaki Tateishi; Yuji Watanabe - Web page: https://patentgrep.com/patent/US20130159696A1 ## CPC - H04L 9/08: Key distribution {or management, e.g. generation, sharing or updating, of cryptographic keys or passwords (network architectures or network communication protocols for supporting key management in a packet data network H04L63/06)} - G06F 16/285: {Clustering or classification} - H04L 9/14: using a plurality of keys or algorithms - H04L 9/3006: {underlying computational problems or public-key parameters} - H04L 63/06: {for supporting key management in a packet data network (cryptographic mechanisms or cryptographic arrangements for key management H04L9/08)} - H04L 2209/50: Oblivious transfer - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract A system includes a server connectable to a client, the server configured to allow the client to acquire a message of an index designated by the client among N messages held by the server where N is an integer of two or more. The server includes a classification unit configured to classify the N messages into M classified messages by contents of the messages; a message encryption unit configured to encrypt each of the M classified messages; a message provision unit configured to provide the M encrypted classified messages to the client; and a key sending unit configured to send the client, by oblivious transfer, a message key for decrypting the classified message corresponding to the message of the index designated by the client. ## Claims ### Claim 1 A system, comprising: a server connectable to a client, the server configured to allow the client to acquire a message of an index designated by the client among N messages held by the server where N is an integer of two or more, the server further comprising: a classification unit configured to classify the N messages into M classified messages by contents of the messages; a message encryption unit configured to encrypt each of the M classified messages; a message provision unit configured to provide the M encrypted classified messages to the client; and a key sending unit configured to send the client, by oblivious transfer, a message key for decrypting the classified message corresponding to the message of the index designated by the client. ### Claim 2 (depends on 1) The system according to claim 1, wherein the client comprises: a key reception unit configured to receive the message key for the message of the designated index from the server by the oblivious transfer; and a message decryption unit configured to decrypt the classified message corresponding to the message of the designated index by using the received message key among the M encrypted classified messages provided from the server. ### Claim 3 (depends on 2) The system according to claim 2, wherein the key sending unit sends the client a pointer together with the message key by the oblivious transfer, the pointer indicating the classified message which is decryptable by using the message key sent to the client among the M encrypted classified messages. ### Claim 4 (depends on 3) The system according to claim 3, wherein the key reception unit receives the pointer together with the message key, and the message decryption unit decrypts the classified message indicated by the pointer, by using the received message key. ### Claim 5 (depends on 1) The system according to claim 1, wherein the message provision unit sends the client the M encrypted classified messages through a network. ### Claim 6 (depends on 5) The system according to claim 5, wherein the message provision unit sends the client the M encrypted classified messages before the client designates the index. ### Claim 7 (depends on 1) The system according to claim 1, wherein the message provision unit provides the client with the M encrypted classified messages arranged in ascending order of data size. ### Claim 8 (depends on 1) The system according to claim 1, wherein the message provision unit provides the client with the M encrypted classified messages arranged in random order changed from the original arrangement order of the N messages. ### Claim 9 (depends on 1) The system according to claim 1, wherein the client further comprises a classified message storage unit configured to store the M encrypted classified massages in advance prior to the designation of the index. ### Claim 10 A server implemented method of allowing a client to acquire a message of an index designated by the client among N messages held by a server where N is an integer of two or more, the method comprising: classifying, by the server, the N messages into M classified messages by contents of the messages; encrypting each of the M classified messages; providing the M encrypted classified messages to the client; and sending the client, by oblivious transfer, a message key for decrypting the classified message corresponding to the message of the index designated by the client. ### Claim 11 (depends on 10) The method according to claim 10, wherein the client is configured to: receive the message key for the message of the designated index from the server by the oblivious transfer; and decrypt the classified message corresponding to the message of the designated index among the M encrypted classified messages provided from the server, by using the received message key. ### Claim 12 (depends on 2) The method according to claim 2, wherein the server sends the client a pointer together with the message key by the oblivious transfer, the pointer indicating the classified message which is decryptable by using the message key sent to the client among the M encrypted classified messages. ### Claim 13 (depends on 12) The method according to claim 12, wherein the server is configured to receive the pointer together with the message key, and the message decryption unit is configured to decrypt the classified message indicated by the pointer, by using the received message key. ### Claim 14 (depends on 10) The method according to claim 10, wherein the server sends the client the M encrypted classified messages through a network. ### Claim 15 (depends on 14) The method according to claim 14, wherein the server sends the client the M encrypted classified messages before the client designates the index. ### Claim 16 (depends on 10) The method according to claim 10, wherein the server provides the client with the M encrypted classified messages arranged in ascending order of data size. ### Claim 17 (depends on 10) The method according to claim 10, wherein the server provides the client with the M encrypted classified messages arranged in random order changed from the original arrangement order of the N messages. ### Claim 18 (depends on 10) The method according to claim 10, wherein the client is configured to store the M encrypted classified massages in advance prior to the designation of the index.