Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-02-17
2001-05-01
Kuntz, Curtis (Department: 2643)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S410000, C455S411000, C379S144020, C379S145000, C379S357040, C235S380000, C235S451000
Reexamination Certificate
active
06226530
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of detecting fraud involving an electronic memory card of given operating frequency used in a telephone set.
A particularly advantageous application of the invention lies in combatting fraudulent calls set up from a telephone set, particularly but not exclusively a public telephone set.
BACKGROUND OF THE INVENTION
Descriptions of memory card technology in popular electronic journals, and in technical training establishments, have greatly contributed to attempts at making fraudulent use of telephone sets by emulating electronic memory cards or “phone cards” designed to operate with such telephone sets. Furthermore, the widespread commercial availability of highly technical components, such as programmed microprocessors, and the ease with which they can be used as acquired in school laboratories or from the programmers of microprocessors, means that this type of fraud can be expected to increase.
There exist two broad categories of phone card simulators, namely:
wired 1 gic simulators known as “passive” simulators which imitate a phone card by connecting together discrete components; and
programmed logic simulators, known as “active” simulators, which are devices essentially comprising a programmed microcontroller associated with a few passive components (resistors, capacitors). By means of an internal program, the microcontroller simulates the behavior of a phone card. Components of that type are now widely available on the non-professional market, as are tools for programming and development, in particular in the form of software running on personal computers.
In general, phone card fraud consists in connecting the active or passive simulator to the electrical contact zones of the electronic module of the card via connection wires, so as to connect the electronic simulator to the telephone set. In order to detect that type of fraud, the telephone set is provided with a specific device known as an external connection detector (ECD). The detector device is mainly constituted by a large and plane electrode suitable for overlaying the connection wires connecting the simulator to the contact zones. When there are no fraudulent connection wires, the only electrical capacitance present between the card and said electrode is a capacitance C
0
due to the environment of the card and the electronics. However, the presence of fraudulent connection wires creates a distributed capacitance C
1
between the plane electrode and the contacts of the pay phone terminal. An ECD is thus based on the principle of detecting an increase in capacitance from C
0
to C
0
+C
1
when a phone card is inserted having connection wires fitted thereto and leading to a simulator.
ECD detection suffers from the drawback that the extra capacitance C
1
drifts with temperature and humidity, which means that in order to obtain best performance in terms of number of wires to be detected, it must have automatic correction based on hardware or semi-automatic correction based on software. It is then advantageous to make use of a differential circuit so as to cancel out the effects of the drift in the extra capacitance.
SUMMARY OF THE INVENTION
Specifically for the purpose of avoiding the above-specified drawback, the present invention provides a method of detecting fraud concerning an electronic memory card having a given operating frequency and used in a telephone set. The invention applies an excitation signal of variable frequency to said card, records a response pattern supplied by the card at a low excitation frequency, and determines that fraud is taking place in the event of said response pattern being deformed at an excitation frequency that is lower than the operating frequency of the card.
As explained in greater detail below, the method of the invention makes it possible to detect the fraudulent presence of an active phone card simulator by making use of the fact that simulation of a phone card by programmed logic can be done only on the basis of a microcontroller together with a programmed algorithm which can operate correctly only up to a maximum frequency Fs which depends on the clock specific to the microcontroller and on the number of cycles required to enable the algorithm to operate, whereas the operating frequency of a phone card depends solely on the technological characteristics of the component. Generally, for the widely available microcontrollers that might be used for fraudulent purposes, this maximum frequency Fs is well below that of an authentic component.
If no deformation of the response pattern is observed at a frequency lower than the operating frequency of the card, it can only be deduced that there is no active simulator based on a microcontroller, which does not mean, however, that there is no simulator at all, since a passive simulator based on wired logic behaves exactly like an authentic phone card in response to the excitation signal delivered by the pay phone.
In order to detect the presence of such a passive simulator, the invention performs an impossible write operation and then reads back that bit. A determination is made that fraud is taking place when the read-back is successful. Only fraudulent phone cards are capable of writing to memory under write conditions that are impossible for authentic cards.
Similarly, still for the purpose of detecting passive simulators, the invention applies an additional step of performing a memory read operation on a number of bits greater than the number of bits in the memory. With an authentic card, above the number of bits in the memory, addressing restarts from zero and bits are read back starting again from the first bit, whereas reading from a fraudulent card will be undefined.
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patent: 5416423 (1995-05-01), De Borde
patent: 5434387 (1995-07-01), Diehl et al.
patent: 5478996 (1995-12-01), Muto et al.
patent: 5510720 (1996-04-01), Vauclin
patent: 5923191 (1999-07-01), Nemetz et al.
patent: 5945662 (1999-08-01), Vallat
patent: 682 520 (1993-09-01), None
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patent: 2 640 061 (1990-06-01), None
Barakat Simon
Cavailles Charles
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Kuntz Curtis
Schlumberger Systemes
Taylor Barry W
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