# US 8,787,573 B2 · Cipher communication method and apparatus for the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,573 B2 - Document ID: US8787573B2 - Status: Granted - Kind: B2 - Application number: 13/572,458 - Filed: 2012-08-10 - Published: 2013-11-21 - Granted: 2014-07-22 - Earliest claimed: 2012-05-17 - Assignees: Electronics and Telecommunications Research Institute - Applicants: Taek-Jun Nam; Byeong-Ho Ahn - Inventors: Taek-Jun Nam; Byeong-Ho Ahn - Web page: https://patentgrep.com/patent/US8787573B2 ## CPC - H04L 63/0428: {wherein the data content is protected, e.g. by encrypting or encapsulating the payload} - H04L 63/068: {using time-dependent keys, e.g. periodically changing keys (cryptographic mechanisms or cryptographic arrangements for controlling usage of secret information H04L9/088)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A cipher communication method for an encryption apparatus an includes: receiving a second encryption key while performing a cipher communication using a first encryption key; storing encryption key input information on the first and second encryption keys in a static region; copying the stored encryption key input information into a dynamic region; selecting any one of the first and second encryption keys based on the copied encryption key input information and current time information; generating encryption key position information and encryption key selection information on the selected encryption key; and transmitting a cipher text and the encryption key selection information to another encryption apparatus connected to the encryption apparatus through a network such that the another encryption apparatus acquires an encryption key to decrypt the cipher text. ## Claims ### Claim 1 A cipher communication method of an encryption apparatus for seamless cipher communication with another encryption apparatus, the method comprising: receiving a second encryption key from another encryption apparatus connected to the encryption apparatus over a network while the encryption apparatus is using a first encryption key to make a cipher communication; storing encryption key input information on the first encryption key and the second encryption key in a static region; copying the stored encryption key input information into a dynamic region; selecting any one of the first and second encryption keys by comparing the copied encryption key input information on the first encryption key, the copied encryption key input information on the second encryption key, and current time information; generating encryption key position information and encryption key selection information on the selected encryption key; and transmitting a cipher text and the encryption key selection information to the other encryption apparatus such that the other encryption apparatus acquires an encryption key to decrypt the cipher text. ### Claim 2 (depends on 1) The cipher communication method of claim 1, wherein the encryption key selection information comprises 0 or 1. ### Claim 3 (depends on 2) The cipher communication method of claim 2, wherein the encryption key selection information is generated as 0 when the selected encryption key is an encryption key of which the start time is faster between the first and second encryption keys, and generated as 1 when the selected encryption key is an encryption key of which the start time is slower between the first and second encryption keys. ### Claim 4 (depends on 1) The cipher communication method of claim 1, wherein the encryption key input information comprises information about encryption key, an encryption key start time, and an encryption key end time. ### Claim 5 (depends on 1) The cipher communication method of claim 1, wherein the storing the encryption key input information on the first and second encryption keys in the static region comprises storing the encryption key input information on the first encryption key and the encryption key input information on the second encryption key in different regions from each other among regions included in the static region. ### Claim 6 (depends on 1) The cipher communication method of claim 1, further comprising: comparing position information of the selected key within the static region to position information of the key within the dynamic region; and when the position information of the selected key within the static region is different from the position information of the key within the dynamic region, copying the corresponding key into the dynamic region from the static region and updating the position information of the key. ### Claim 7 (depends on 1) The cipher communication method of claim 1, further comprising: receiving a fourth encryption key while performing a cipher communication using a third encryption key; storing encryption key input information on the third and fourth encryption keys in a static region; copying the stored encryption key input information into a dynamic region; receiving encryption key selection information and a cipher text from another encryption apparatus; selecting an encryption key to decrypt the received cipher text based on the received encryption key selection information and the encryption key input information copied into the dynamic region; and decrypting the cipher text based on the selected encryption key. ### Claim 8 An encryption apparatus for seamless cipher communication with another encryption apparatus, comprising: an interface unit configured to receive a second encryption key from another encryption apparatus connected to the encryption apparatus over a network while performing a cipher communication using a first encryption key; a storage management unit configured to store encryption key input information on the first and second encryption keys in a static region and store the stored encryption key input information in a dynamic region; and a controller configured to select any one of the first and second encryption keys by comparing the copied encryption key input information on the first encryption key, the copied encryption key input information on the second encryption key, and current time information, generate encryption key position information and encryption key selection information on the selected encryption key, and transmit a cipher text and the encryption key selection information to the other encryption apparatus such that the other encryption apparatus acquires an encryption key to decrypt the cipher text. ### Claim 9 (depends on 8) The encryption apparatus of claim 8, wherein the storage management unit stores the encryption key input information on the first encryption key and the encryption key input information on the second encryption key in different regions from each other among regions included in the static region. ### Claim 10 (depends on 8) The encryption apparatus of claim 8, wherein the encryption key input information comprises information about encryption key, an encryption key start time, and an encryption key end time. ### Claim 11 (depends on 8) The encryption apparatus of claim 8, wherein the encryption key selection information comprises 0 or 1. ### Claim 12 (depends on 11) The encryption apparatus of claim 11, wherein the controller compares starts times of the first and second encryption keys, generates the encryption key selection information as 0 when the selected key is an encryption key of which the start time is faster between the first and second encryption keys, and generates the encryption key selection information 1 when the selected key is an encryption key of which the start time is slower. ### Claim 13 (depends on 8) The encryption apparatus of claim 8, wherein the controller compares position information of the selected key within the static region to position information of the key within the dynamic region, and copies the corresponding key into the dynamic region from the static region to update the position information of the key, when the position information of the selected key within the static region is different from the position information of the key within the dynamic region. ### Claim 14 (depends on 8) The encryption apparatus of claim 8, wherein the interface unit receives a fourth encryption key while performing a cipher communication using a third encryption key, wherein the storage management unit stores encryption key input information on the third and fourth encryption keys in the static region, and copies the stored encryption key input information into the dynamic region, and wherein the controller selects an encryption key to decrypt the received cipher text based on the received encryption key selection information and the encryption key input information copied into the dynamic region, and decrypts the cipher text based on the selected encryption key, when encryption key selection information and a cipher text are received from another encryption apparatus.