1997-01-13
1998-11-24
Nguyen, Hoa T.
Excavating
365201, G11C 2900, G11C 700
Patent
active
058417869
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the testing of the content of memory associated with a microprocessor. The memory may be memory whose contents cannot be altered (Read Only Memory or ROM) or memory whose contents can be altered such as Electrically Programmable Read Only Memory (EPROM) or RAM (Random Access Memory).
There are many instances in which memory which holds predetermined information is required to be tested. An example is in the use of integrated credit cards, otherwise know as smart cards. Conventionally, smart card memory is tested by connecting the card to a reader, reading out the memory contents and performing a check on the readout, perhaps by way of check-sum verification or by comparison of the read-out with data which should be present. Often, the memory contents are confidential and it is possible that unauthorised access to the information could be obtained by simulating a memory test. An object of the invention is to overcome this problem.
According to a first aspect of the invention there is provided a method of testing the proper functioning of an electrically alterable memory associated with an integrated circuit, the method consisting in writing test data to the memory, applying predetermined data as input to the integrated circuit, comparing the data internally within the integrated circuit with the test data held in the memory, and issuing a verification output from the integrated circuit whereby the write function and the retention properties of the memory may be verified as correct or not according to the verification output.
By this method, the write function and retention properties of an electrically alterable memory can be tested.
According to a second aspect of the invention there is provided a method of testing the content of memory associated with a microprocessor in a module, the method consisting in applying predetermined data as input to the module, encrypting the predetermined data, comparing the encrypted predetermined data internally within the module with data held in the memory and issuing a verification output from the module according to whether the memory content is verified as correct or not by the comparison.
According to the second aspect of the present invention, the data held in the memory may be data permanently or semi-permanently resident in the memory, such as program data and/or initialisation data, or it may be data written to the memory as a first step in the test method. By this latter method, the write function and retention properties of an electrically alterable memory can be tested.
The module may be an integrated circuit including the memory and the microprocessor or may be a set of integrated circuits physically bonded by encapsulation or the like. Typically the module is an integrated circuit in a smart card.
By use of an internal memory comparison technique as described above the memory contents are externally inaccessible directly. All that is output is a verification signal.
It is possible that fraudulent attempts to determine the content of the memory may be made by automatically inputting successive sets of test data which are systematically changed in content until a verification output indicates that the memory content corresponds with the input data. There are ways of dealing with this problem.
According to a feature of the invention the microprocessor is programmed to delay the issue of each verification or non-verification output. The delay between successive outputs may be a matter of microseconds or seconds. The object is to render the time taken for systematic checking to be prohibitively long.
Another way of preventing fraudulent memory checking is to arrange that the input data is encrypted, for example by being operated on by a secret algorithm, before comparison. Then the input data would have no clear correlation with the memory content. The algorithm or a key to it could be different from batch to batch of the smart cards.
The invention will further be described with reference to the accompanying drawing, of which the sole FIGU
REFERENCES:
patent: 4782486 (1988-11-01), Lipcon et al.
patent: 5568437 (1996-10-01), Jamal
National Westminster Bank PLC
Nguyen Hoa T.
LandOfFree
Testing of memory content does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Testing of memory content, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Testing of memory content will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1711236