Semiconductor memory card and computer readable program
View Patent ↗The present invention provides a semiconductor memory card which no longer allows an illegal practice of acquiring contents of a deleted file. Here, when a deletion event is generated, a deletion handler gives a priority to a null-clear operation of a file entry and a FAT for a file to be deleted over a null-clear operation to other constituents of the file. A null-clear operation to a file entity of the file is distributed to a plurality of event handlers including the deletion handler.
1. A semiconductor memory card comprising:
a nonvolatile memory that stores a file constituted by an entity and management information; and
a tamper-resistant module that includes a processing unit and an internal memory, the processing unit including:
an analysis unit operable to analyze a command issued by a device to which the semiconductor memory card is connected and generate an event corresponding to a result of the analysis; and
a deletion unit operable to, if a deletion event for the file is generated, (i) create a location table on the internal memory in the tamper-resistant module, and (ii) overwrite the management information, wherein
the location table indicates a location of the entity, and is referred to by the deletion unit when the deletion unit overwrites the entity,
the internal memory stores an encryption key with which the entity has been encrypted, and
the deletion unit includes:
a main deletion unit operable to, if the deletion event is generated, first overwrite the encryption key with which the entity has been encrypted and subsequently create the location table and overwrite the management information; and
a sub deletion unit operable to, if an event different from the deletion event is generated, overwrite the entity with reference to the created location table.
2. The semiconductor memory card of claim 1 , wherein
the deletion event is generated by the analysis unit wben the device to which the semiconductor memory card is connected issues a command to delete the file, and
the different event is a command-end event that is generated by the analysis unit when the processing unit completes the operation corresponding to the command.
3. The semiconductor memory card of claim 1 , wherein
the deletion event is generated by the analysis unit when the device to which the semiconductor memory card is connected issues a command to delete the file, and
the different event is one of a reading event and a writing event, the reading event being generated by the analysis unit when the deviee issues a command to read a different file in the semiconductor memory card, and the writing event being generated by the analysis unit when the device issues a command to write to the different file in the semiconductor memory card.
4. The semiconductor memory card of claim 3 , wherein
the main deletion unit is a deletion handler that starts operating in response to the generation of the deletion event, and
the sub deletion unit is included in a reading/writing handler that starts operating in response to the generation of one of the reading event and the writing event.
5. The semiconductor memory card of claim 1 , wherein
the management information of the file has been encrypted with an encryption key which is different from the encryption key for the entity, the encryption key for the management information being stored in the internal memory, and
when the deletion event is generated, the main deletion unit overwrites the encryption key for the management information before overwriting the encryption key for the entity.
6. The semiconductor memory card of claim 1 , wherein
the entity of the file is divided into fragments, and
the location table shows (i) a start address of each of the fragments constituting the entity, and (ii) a flag which is set as “OFF” if each of the fragments has not been completely overwritten and set as “ON” if the fragment has been completely overwritten.
7. The semiconductor memory card of claim 1 , wherein
the semiconductor memory card operates by means of either contact or contactless power supply from a device, and
the processing unit performs the overwriting only when the semiconductor memory card operates by means of the contact power supply from the device.
8. The semiconductor memory card of claim 1 wherein
the nonvolatile memory is constituted by a first memory module and a second memory module,
a unit of writing for the second memory module is smaller than a unit of writing for the first memory module, and
the management information is stored in the second memory module.
9. The semiconductor memory card of claim 8 , wherein
the second memory module is one of a Ferro Electric Random Access Memory and a Magnetoresistant Random Access Memory.
10. The semiconductor memory card of claim 1 , wherein
the internal memory is constituted by a first memory module and a second memory module,
a unit of writing for the second memory module is smaller than a unit of writing for the first memory module, and
the location table is stored in the second memory module.
11. The semiconductor memory card of claim 10 , wherein
the second memory module is one of a Ferro Electric Random Access Memory and a Magnetoresistant Random Access Memory.
12. A control program embodied on a computer-readable medium, the control program being executed by a CPU in a tamper-resistant module included in a semiconductor memory card, the tamper-resistant module including an internal memory, and the semiconductor memory card including a nonvolatile memory for storing a file constituted by an entity and management information, the control program causing the CPU to execute:
an analysis step of analyzing a command issued by a device to which the semiconductor memory card is connected and generating an event corresponding to a result of the analysis; and
a deletion step of, if a deletion event for the file is generated, (i) creating a location table on the internal memory in the tamper-resistant module, and (ii) overwriting the management information, wherein
the location table indicates a location of the entity, and is referred to by the control program when the control program overwrites the entity,
the internal memory stores an encryption key with which the entity has been encrypted,
the deletion step includes:
a main deletion step of, if the deletion event is generated, first overwriting the encryntion key with which the entity has been encrypted and subsequently creating the location table and overwriting the management information; and
a sub deletion step of, if an event different from the deletion event is generated, overwriting the entity with reference to the created location table.