# US 5,708,710 A · Method and apparatus for authentication in a communication system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,710 A - Document ID: US5708710A - Status: Granted - Kind: A - Application number: 08/493,951 - Filed: 1995-06-23 - Granted: 1998-01-13 - Earliest claimed: 1995-06-23 - Assignees: Motorola, Inc. - Inventors: Michael C. Duda - Web page: https://patentgrep.com/patent/US5708710A ## CPC - H04L 9/0891: {Revocation or update of secret information, e.g. encryption key update or rekeying} - H04L 9/3271: {using challenge-response} - H04L 2209/80: Wireless - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method and apparatus for performing authentication in a communication system. The method includes the steps of detecting an unexpected authentication message, updating a counter value, comparing the counter value to a threshold value, and performing an encryption key update operation in response to the comparison between the counter value and the threshold value. The apparatus includes a base station (152), a switching center (128) coupled to the base station (152), and an authentication center (149) responsive to the switching center (128). The switching center (128) detects an unexpected authentication message received by the base station (152). The authentication center (149) updates a counter when the switching center (128) detects the unexpected authentication message and compares the updated counter with a threshold value. The authentication center (149) initiates an encryption key update operation when the updated counter value exceeds the threshold value. ## Claims ### Claim 1 A method of performing authentication in a communication system comprising the steps of: detecting an unexpected authentication message, said unexpected authentication message including but not limited to at least one of the following: an unsolicited base station challenge message; and an unsolicited unique challenge response message; updating a counter value; comparing the counter value to a threshold value; and performing an encryption key update operation in response to the comparison between the counter value and the threshold value. ### Claim 2 (depends on 1) The method of claim 1, wherein the encryption key comprises shared secret data (SSD). ### Claim 3 (depends on 1) The method of claim 1, wherein the encryption key comprises an A-key value. ### Claim 4 (depends on 1) The method of claim 1 wherein the unsolicited base station challenge message comprises a received base station challenge message that is not in repose to prior encryption key update message. ### Claim 5 (depends on 1) The method of claim 1 wherein the unsolicited unique challenge response message comprises a received unique response message that is not in response to a prior unique challenge message. ### Claim 6 (depends on 1) The method of claim 1, wherein a plurality of unexpected authentication messages are detected and the counter value is updated in response to the detection of each of the plurality of unexpected authentication messages. ### Claim 7 (depends on 1) The method of claim 1, further comprising the steps of: updating a second counter value; comparing the second counter value to a second threshold value; and performing a second encryption key update operation in response to the comparison between the second counter value and the second threshold value. ### Claim 8 An apparatus for performing authentication in a communication system comprising: a base station receiving an unexpected authentication message, said unexpected authentication message including but not limited to at least one of the following: an unsolicited base station challenge message; and an unsolicited unique challenge response message; a switching center coupled to the base station; a counter that is updated in response to the received unexpected authentication message; and an authentication center responsive to the switching center, said authentication center initiating an encryption key update operation when the counter exceeds a threshold value. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein said authentication center is incorporated into the switching center. ### Claim 10 (depends on 8) The apparatus of claim 8, wherein the encryption key comprises shared secret data (SSD). ### Claim 11 (depends on 8) The apparatus of claim 8, wherein the encryption key comprises an A-KEY value. ### Claim 12 (depends on 8) The apparatus of claim 8 wherein the unsolicited base station challenge message comprises a received base station challenge message that is not in response to a prior encryption key update message. ### Claim 13 (depends on 8) The apparatus of claim 8, wherein the mobile switching center detects a plurality of unexpected authentication messages and the counter is updated in response to the detection of each of the plurality of unexpected authentication messages. ### Claim 14 (depends on 8) The apparatus of claim 8, wherein said communication system comprises a wireless communication system. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein said wireless communication system comprises a system selected from the group consisting of a code division multiple access, a time division multiple access, and a frequency division multiple access cellular system. ### Claim 16 A method of performing authentication in a communication system comprising the steps of: receiving a base station challenge message at a base station; determining whether the received base station challenge message is an unexpected authentication message by determining whether a prior shared secret data (SSD) update order was sent by the base station; incrementing a first counter if the received base challenge message is an unexpected authentication message; comparing the first counter to a first threshold value; performing an SSD key update and incrementing a second counter if the first counter exceeds the first threshold value; comparing the second counter with a second threshold value; and performing an A-key update if the second counter exceeds the second threshold value.