Mobile communication terminal device and method of preventing improper rewriting of information

Abstract: In a mobile communication terminal device, a serial number for use in charging control of a subscriber and so on is prevented from being incorrectly rewritten and hence the subscriber is prevented from being incorrectly charged. An electrically writable/erasable memory 10 in the mobile communication terminal device includes a first storage region RG1 for storing information as an encoded serial number and a storage region RG2 for storing said serial number before encoding, and further a CPU 2 includes means for decoding said encoded information and comparing it with said serial number, and disabling the mobile communication terminal upon incoincidence being noted.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication terminal system, and more specifically to a mobile communication terminal device such as that in portable telephone sets and mobile phones capable of preventing pieces of information such as serial numbers each for use in charging control of subscribers and so on from being improperly or otherwise incorrectly rewritten and to a method of preventing information from being improperly or incorrectly rewritten. 2. Description of the Prior Art Referring to FIG.1, a prior art mobile communication terminal device is illustrated which comprises a CPU 2, an EEPROM 3 as a ROM capable of electrical writing/erasing, a ROM 4, a RAM 5, a TRX as a transmitter/receiver section, an antenna 7, an interface (I/O) 8, and an I/O connector 9. Herein, upon writing in a storage region RG in the EEPROM 3 a serial number (hereinafter, referred to as ESN) for use in charging control and so on, the CPU 2 receives and analyzes ESN data fed through the I/O connector 9 and the interface 8, and thereafter writes the same in the storage region RG. When the mobile communication terminal device 1 makes a call, the ESN is sent to a base station as data together with a MIN (Mobile Indentification Number) as a subscriber's number. In the base station, it is judged on the basis of the received data whether coincidence is attained or not between the combination of the ESN and the MIN and a previously registered corresponding combination, and if so a subscriber identified by that number is charged. In this case, if any information concerning a subscriber's ESN and MIN could improperly be obtained and his ESN and MIN could be written in another person's mobile communication terminal 1, the original subscriber would be wrongly charged. The MIN has to be rewritten after shipping, but the ESN, which is the number inherent in and particularly to the device, does not need to be rewritten after it is once written upon shipping. Further the ESN has no limitation to its writing, and hence it is rewritable with ease once the method of its writing is known. Such a prior art mobile communication terminal device therefore has a difficulty that an ESN written in an EEPROM may be rewritten with ease by investigating a storage address of the ESN in the EEPROM and rewriting that data. JP-A-03.099.532 discloses a method of preventing illicit use of a cellular mobile communication terminal in which the ESN is duplicated in a second ROM. In operation, the two ESNs are compared. If they coincide, the terminal performs the normal processing. If they are different, the terminal is disabled. SUMMARY OF THE INVENTION To solve the difficulty with the prior art, it is a first object of the present invention to provide a mobile communication terminal device wherein effective use of the device is frustrated if information inherent to the device such as the ESN is rewritten. In such circumstances, the result is that unauthorised or improper rewriting of the inherent information is prevented by rendering it nugatory. It is a second object of the present invention to provide in a mobile communication terminal device a method of preventing or otherwise frustrating incorrect rewriting of information inherent to the device. To achieve the above objects, in one aspect the invention provides a mobile communication terminal device comprising an electrically writable/erasable memory having a first storing area and a second storing area for storing information particular to the device, characterised in that said information is stored in said first storing area in an encoded form and in said second storing area in a non-encoded form, said memory further having a third storing area for storing data, inherent to the encoded information, in either a first state in which the rewriting of both the information in said second storing area and the data in said third storing area is permanently prohibited and a second state in which such rewriting is allowed; said device further comprising means for permanently disabling rewriting of said information in said first and second storing area and of said data in said third storing area if said data is in said first state; means for decoding the stored encoded information; means for comparing the decoded information with the stored non-encoded information prior to energising the device; and means for disabling effective operation of the device if the non-encoded information is not identical with the decoded information. The invention also provides a method of preventing information inherent in a mobile communication device from being incorrectly rewritten, said method being characterised by comprising the steps of storing said information in an electrically writable/erasable memory both in an encoded form and in a non-encoded form; storing data, inherent to the encoded information, in either a first state in which the rewriting of both the information in said second storing area and the data in said third storing area is permanently prohibited and a second state in which such rewriting is allowed; permanently disabling rewriting of said information in said first and second storing area and said of said data in said third storing area if said data is in said first state; decoding said encoded stored information prior to initiation of speech operation after power is supplied to the device and comparing the decoded information with said stored non-encoded information; and disabling the speech operation if the non-encoded information is not coincident with the decoded information. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative examples. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a block diagram schematically illustrating a prior art mobile communication terminal device; FIG.2 is a block diagram schematically illustrating a mobile communication terminal device according to the present invention; FIG.3 is a flow chart illustrating a method of preventing incorrect rewriting according to the present invention; and FIG.4 is a flow chart illustrating writing of a serial number (ESN) in the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT In what follows, an embodiment of the present invention will be described with reference to the accompanying drawings. Referring to FIG.2, there is provided a block diagram illustrating a mobile communication terminal device as an embodiment of the present invention. In FIG.2, symbols identical to those of the prior art example illustrated in FIG.2 have the same functions. In the present embodiment, an EEPROM 10 includes two storage areas: a RG1 for storing an ESN(E) after encoded and a RG2 for storing an ordinary ESN(D) before encoded. Referring to FIG.3, there is illustrated a method of writing ESN data according to the present invention. With a writing request upon shipping in step F-1, a CPU 2 confirms an ESN writing level in step F-2. If the writing is allowed, then the ESN(E) encoded in conformity with a predetermined encoding format is inputted through an I/O connector 9 in step F-3. The CPU 2 reads the encoding format and a check code both stored in the ROM 4, and checks that the encoded ESN(E) inputted through the I/O connector 9 is correctly encoded in step F-4. If it is correct, then the encoded ESN(E) is written in the storage region RG2 of the EEPROM 10 in step F-5. Thereafter, the encoded ESN(E) is decoded in step F-6, and an ordinary ESN(D) so decoded is written in the storage region RG1 of the EEPROM 10 in step F-7. Although a writing level of such an ESN in general should not be altered after the inherent ESN is written in the EEPROM 10 because rewriting thereafter should be prohibited, there is sometimes a need for the ESN to be rewritten owing to unexpected alteration of the destination of shipping. For this, it is investigated whether or not the writing level of the ESN has been altered in step F-8. If it has been altered, then writing of ESNs thereafter becomes a prohibition state in step F-9. Unless the the writing level of the ESN is altered, then the present ESN writing level is held for the purpose of writing of ESNs thereafter in step F-10. The writing prohibition state or the holding of a writing level, ie. a writing permission state is stored in a storage region of the EEPROM 10 not illustrated (different from the storage regions RG1 and RG2). If it is now later attempted to re-write the ESN, then a writing request of the ESN is existent as in the step F-1. The CPU 2 successively confirms the writing level of the ESN as in the step F-2. As a result, since the writing of the ESN has been prohibited in step F-9, (the ESN writing level having been altered in the step F-8), the writing of the new ESN, is denied in step F-11 and the ESN already written is destroyed in step F-12 to disable the mobile communication terminal device 1. Hereby, incorrect rewriting of the ESN after shipping is prevented. Any mobile communication terminal device once prohibited as such in writing thereinto is impossible to be altered without replacing the EEPROM for a new one. Referring to FIG. 4, there is illustrated a method of preventing incorrect charging according to the present invention. With a power supply turned on by a subscriber upon the use of the mobile communication terminal device 1, the CPU2 reads and decodes the encoded ESN(E) stored in the storage region RG2 of the EEPROM 10 in step P-2, and further reads the decoded ESN(D) from the storage region RG1 of the EEPROM 10 in step P-3, for comparison therebetween in step P-4. As a result, if both are coincident, then the operation advances ordinary speech operation in step P-5, but if they are not coincident, then the operation is directed to displaying the prohibition and the device is disabled in step P-6. The comparison in the step P-4 detects non-coincidence if the ESN has been improperly rewritten, and hence chargeable use of the device is prevented, and no incorrect charge is billed to the original subscriber's account. According to the present invention, as described above, an ESN is doubly stored in the EEPROM, and both are compared upon power supply being turned on, so that even though an incorrect user rewrites one thereof, the mobile communication terminal device is prevented from being incorrectly used owing to incorrect rewriting of the ESN. Further, since one of the ESNs doubly stored is encoded, both ESNs are unlikely to be rewritten simultaneously, thus safeguarding against incorrect use of the ESN.

Claims: A mobile communication terminal device comprising; an electrically writable/erasable memory (10) having a first storing area (RG2) and a second storing area (RG1) for storing information particular to the device, characterised in that said information is stored in said first storing area in an encoded form and in said second storing area in a non-encoded form, said memory further having a third storing area for storing data, inherent to the encoded information, in either a first state in which the rewriting of both the information in said second storing area and the data in said third storing area is permanently prohibited and a second state in which such rewriting is allowed; said device further comprising: means for permanently disabling rewriting of said information in said first and second storing area and of said data in said third storing area if said data is in said first state; means for decoding the stored encoded information; means for comparing the decoded information with the stored non-encoded information prior to energising the device; and means for disabling effective operation of the device if the non-encoded information is not identical with the decoded information. The mobile communication terminal device according to Claim 1, wherein the information is a serial number of the device. A method of preventing information inherent in a mobile communication device from being incorrectly rewritten, said method being characterised by comprising the steps of: storing said information in an electrically writable/erasable memory (10) both in an encoded form and in a non-encoded form; storing data, inherent to the encoded information, in either a first state in which the rewriting of both the information in said second storing area and the data in said third storing area is permanently prohibited and a second state in which such rewriting is allowed; permanently disabling rewriting of said information in said first and second storing area and said of said data in said third storing area if said data is in said first state; decoding said encoded stored information prior to initiation of speech operation after power is supplied to the device and comparing the decoded information with said stored non-encoded information; and disabling the speech operation if the non-encoded information is not coincident with the decoded information. A method according to Claim 3, wherein said stored information is a serial number of said mobile transmission terminal device. A method according to Claim 3 or Claim 4, wherein said comparison between said decoded information and said non-encoded information is performed upon power being supplied to the device.

Inventors: KOMODA MOTOYOSHI, NAMIKI HIDEO, KOMODA, MOTOYOSHI, NAMIKI, HIDEO, KOMODA, MOTOYOSHI, C/O NEC CORPORATION, Namiki, Hideo, c/o NEC Corporation
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1993
Main classification: H04Q7
IPC codes: H04W88, H04M1