Radio telephone hand set network restriction

Details Radio telephone hand set network restriction Radio telephone hand set network restriction

1999-02-10

2001-06-26

To, Doris H. (Department: 2682)

Telecommunications

Radiotelephone system

Security or fraud prevention

C455S575100, C455S528000, C340S005200

Reexamination Certificate

active

06253073

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to mobile phones and in particular it relates to a security function for restricting the use of individual radio telephone hand sets to selected operator networks.
The hand set for which the invention is provided is a digital radio transceiver programmed to operate under the control of a central processing unit (CPU).
(2) Description of the Prior Art
Owing to the variations in pricing policy of network operators, the nominal selling price of mobile phones is often heavily discounted in favour of a higher call tariff. The possibility exists therefore of a user obtaining at very low, or even no cost, a hand set for use on a specified network with a relatively high call tariff. If the hand set were then to be used on a low call tariff network for which the charge for hand sets remained at full selling price then both network operators would be deprived of revenue. It is important to network operators therefore that use of hand sets be restricted to specified networks.
The adaptation of telephone hand sets by copying from or imitating a licensed hand set, normally for unauthorized sale or use, is known as cloning and this definition of cloning is used herein.
Prior art methods for prevention of unauthorized use and prevention of cloning of telephone hand sets include so called secret numbers and U.S. Pat. No. 5,430,892 for example describes a use of secret numbers stored in a ROM (read only memory).
Removal of the ROM from the circuit board of a telephone hand set properly connected to a target network would, however, allow unauthorized copies of the ROM to be obtained. An unscrupulous person would then be in a position to alter very many telephone hand sets merely by supplying the appropriate ROM.
SUMMARY OF THE INVENTION
It is an object of this invention to provide, inexpensively, an increased level of protection against unauthorized use or cloning of mobile telephone hand sets.
According to the invention there is provided a mobile telephone hand set programmed to operate under the control of a CPU and protected against unauthorized use or cloning by means of a security engine, the security engine comprising a re-programmable write only memory, an interface register and a challenge timer and operating by the issue of a challenge from the challenge timer to the CPU, the CPU on receipt of a challenge responding by writing a value to the interface register for comparison therein with a value stored in the re-programmable write only memory and the interface register signaling the result of the comparison.
The above and other objects, features and advantages of the present invention will become apparent from the following description referring to the accompanying drawing which illustrates an example of a preferred embodiment of the present invention.


REFERENCES:
patent: 5021776 (1991-06-01), Anderson et al.
patent: 5430892 (1995-07-01), Motegi
patent: 5457737 (1995-10-01), Wen
IEEE100 The Authoritative Dictionary of IEEE Standards Terms, 7th Edition, See pp. 1286-1287, Dec. 2000.

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