Secure mobile radio telephony

• US 4,549,308 A
• Filed: 07/12/1982
• Issued: 10/22/1985
• Est. Priority Date: 07/12/1982
• Status: Expired due to Fees

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: LoPinto, Frank J.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US06/397,131
• Time in Patent Office: 1,198 Days
• Field of Search: 455/26, 455/27, 179/1.5 R, 178/22.07, 178/22.08, 178/22.12, 178/22.14, 178/22.17, 340/825.34, 235/379, 235/382
• US Class Current: 380/272
• CPC Class Codes: H04B 7/2621 using frequency division multiple access [FDMA] H04B7/2615 takes precedence
• CPC Class Codes: H04L 2209/125 Parallelization or pipelining, e.g. for accelerating processing of cryptographic operations
• CPC Class Codes: H04L 2209/805 Lightweight hardware, e.g. radio-frequency identification [RFID] or sensor
• CPC Class Codes: 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
• CPC Class Codes: H04L 9/0861 Generation of secret information including derivation or calculation of cryptographic keys or passwords
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying
• CPC Class Codes: H04W 12/50 Secure pairing of devices

Abstract

An arrangement for generating an encryption key for use in encrypting communications between a mobile radio telephone unit and a base station is disclosed which can be readily changeable in real time. Each mobile unit is equipped with a machine-readable nonbroadcast code and the base station can access a translation table correlating the nonbroadcast code with the public directory number of the mobile unit. Upon changing frequencies, as for example, when a mobile unit moves from one geographical cell area to another, the current and previous frequencies or channel numbers are left to select sets of digit positions in the nonbroadcast code. The contents of these digit positions are then convolved and inserted into a modified version of the nonbroadcast code generated by convolving the original code with a shifted replica thereof. The key so generated may be used to encrypt communications for the use of any known encrypting circuitry.

Claims

1. An arrangement for generating an encryption key for a mobile radiotelephone unit capable of utilizing any of a group of predetermined communications channel frequencies and having an original, machine-readable plural-bit nonbroadcast code, comprising:

means for forming an altered version of said original machine-readable nonbroadcast code in accordance with criteria defined by communication channel frequencies utilized by said unit, and

means for convolving the contents of respective bit positions of said original and said altered nonbroadcast code with each other to provide said encryption key.

2. An arrangement according to claim 1 wherein said means for forming said altered version of said nonbroadcast code includes means for storing an indication of the frequency of the channel currently in use by said mobile unit and a frequency previously used by said mobile unit,

means controlled by said storing means for identifying respective mutually-exclusive segments of said original nonbroadcast code, and

means for convolving said segments with each other to derive a control segment.

3. An arrangement according to claim 2 wherein said means for forming said altered version of said nonbroadcast code comprises means for rotating said original nonbroadcast code in accordance with the value of said control segment.

4. An arrangement for generating an encryption key for encrypting communications between a mobile radiotelephone unit and a base station capable of communicating over any of a group of changeable communications channel frequencies, said radiotelephone unit having an original, machine-readable plural bit nonbroadcast code, comprising:

means for storing an indication of a currently in-use one of said communications channel frequencies and of another of said communications channel frequencies,

means responsive to each said stored indication for identifying a respective set of bit positions in said original machine-readable nonbroadcast code,

means for performing a binary operation on the contents of each said set of bit positions to derive a further set of bit values, said further set being distinctive from each said set,

means for providing an altered version of said machine-readable nonbroadcast code in accordance with said further set of bit values, and

means for exclusively-ORing said original machine-readable nonbroadcast code with said altered version to produce said encryption key.

5. An arrangement for generating an encryption key for use with a mobile radiotelephone unit capable of employing any of a group of communications channel frequencies, said radiotelephone unit being equipped with an original, machine-readable plural-bit nonbroadcast code, comprising:

means responsive to a change in said communications channel frequencies for forming an altered version of said original plural-bit nonbroadcast code, and

means for convolving said original plural-bit nonbroadcast code with said altered version of said nonbroadcast code to provide said encryption key.

6. A method for generating an encryption key at a base station and at a remote unit from a respectively stored nonbroadcast code, comprising:

convolving the nonbroadcast code with a shifted replica thereof to form a product, and

replacing a predetermined number of bit positions in the convolved product with the result of convolving sets of predetermined bit positions defined by communication channel frequencies used in communications between said base station and said remote unit, in mutually exclusive portions of the nonbroadcast code.