WO2007107417A1

WO2007107417A1 - Method and systems for limiting repeated accesses to an electronic device

Info

Publication number: WO2007107417A1
Application number: PCT/EP2007/051457
Authority: WO
Inventors: Frederic Bauchot; Pierre Secondo; Jean-Yves Clement; Gerard Marmigere
Original assignee: International Business Machines Corporation; Compagnie Ibm France
Priority date: 2006-03-23
Filing date: 2007-02-14
Publication date: 2007-09-27
Also published as: CN101405745A; JP2009530727A; EP1997058A1

Abstract

A system for limiting repeated accesses to an electronic device, particularly to an electronic device receiving power from an external source, is disclosed. According to this system, each consecutive access done to this electronic device in less than a predetermined delay increases a counter that value determines another delay during which electronic device is idle. Preferably, the delay during which electronic device is idle is an exponen- tial function of the counter value. Thanks to this delay, one can not reasonably determine the function of the electronic device by testing a great number of input values, preventing copying this device. According to the invention, the system for limiting repeated accesses to the electronic device comprises, a counter, a counter reset that maintains the value of the counter for a predetermined delay after the power off of the system, and a logic access circuit adapted to increase the value of the counter each time an access is done to the electronic device and to idle the electronic device for a delay depending upon the value of the counter.

Description

METHOD AND SYSTEMS FOR LIMITING REPEATED ACCESSES TO

AN ELECTRONIC DEVICE

Field of the Invention

The present invention relates generally to the methods and systems for controlling the access to data stored within electronic devices and more specifically to a method and systems for limiting repeated attempts to access electronic devices .

Background of the Invention

Conventional method and apparatus exist for making it difficult to counterfeit high value items such as rare wines and perfumes, or documents such as official documents and financial document. A basic concept to assure that the item is genuine requires a form of verification of the item, such as identifiers to confirm the items as being genuine. For example, U.S. Patent Application 2004/0000987 discloses a process for detecting check fraud using Radio Frequency Identifier (RFID) tags. According to this invention, the system comprises a first device for receiving from a payor a request to create a check having a radio frequency identifier (RFID) tag associated therewith. A second device is provided for receiving from a payee a request to validate a check having an RFID tag associated therewith. The system further comprises an RFID repository. A processor is provided for (i) receiving check information from the payor, (ii) updating the RFID repository with check information received from the payor, (iii) receiving scanned check information from the payee, (iv) comparing the scanned check information received from the payee with certain information retrieved from the RFID repository, and (v) determining if the check is valid based upon the comparison of the scanned check information received from the payee with the certain information retrieved from the RFID repository. Preferably, the RFID repository comprises a central RFID repository. Likewise, U.S. Patent 6,226,619 discloses a method and system for preventing counterfeiting of an item, including an answering tag attached to the item. The item includes visible indicia for comparison with secret, non-duplicable information stored in the tag designating authenticity.

According to these methods and systems, it is possible to ensure that a given document has been issued by the relevant person, or that an item has been manufactured by the relevant manufacturer, or that a given official document has been issued by the relevant administration. As mentioned above, these methods and systems are based upon identifiers encoded within the RFIDs however, such identifiers can be duplicated on other RFIDs using a RFID scanner and writer.

Electronic tags such as passive RFID are typical examples of electronic devices which are not equipped with a permanent power source. As mentioned above, such devices may play an important role in many fields, such as security enforcement. Indeed they can record secret information that a hacker may try to crack. One of the easiest and most common strategies followed by hackers is to trigger the RFID tag logic by a sequence of different inputs X₁, to collect the sequence of returned information F(X₁), hopping that the set of samples (X₁, F(X₁)) allows to partially or completely "reverse engineer" the function F that hides the secret information . Therefore, there is a need for a method and systems for limiting the risk of reverse engineering the logic imbedded within the chip of an electronic tag such as an RFID.

Summary of the Invention

Thus, it is a broad object of the invention to remedy the shortcomings of the prior art as described here above.

It is another object of the invention to provide an improved electronic device limiting the repeated accesses.

It is a further object of the invention to provide an improved electronic device limiting the repeated accesses, the repeated accesses being non-destructive.

It is a further object of the invention to provide an improved electronic device receiving power from an external source, adapted to limit the repeated accesses.

It is still a further object of the invention to provide a method for limiting repeated accesses to an electronic device.

The accomplishment of these and other related objects is achieved by a system in an electronic device for limiting repeated accesses to said electronic device, said system comprising,

- counting means;

- counter resetting means adapted to maintain the value of said counting means for a predetermined delay after the power off of said system; and, - logic access means adapted to increase the value of said counting means each time an access is done to said electronic device and to idle said electronic device for a delay depending upon the value of said counting means;

and by a method for limiting repeated accesses to an electronic device, said method comprising the steps of,

- resetting a counter when said electronic device is not accessed during a predetermined delay; incrementing said counter each time said electronic device is accessed;

- setting said electronic device in an idle state for a delay depending upon the value of said counter.

Further embodiments of the invention are provided in the appended dependent claims.

Further advantages of the present invention will become apparent to the ones skilled in the art upon examination of the drawings and detailed description. It is intended that any additional advantages be incorporated herein.

Brief Description of the Drawings

Figure 1 depicts an example of the architecture of a passive RFID tag.

Figure 2 comprises figures 2a and 2b. Figure 2a shows an RFID system with a reader having an antenna and an RFID tag having a dipole antenna. Figure 2b illustrates the signal emitted by the antenna of the reader and the modulated signal reflected by the RFID tag.

Figure 3 illustrates an example of a passive RFID according to the invention for limiting the repeated accesses to the data of the tag.

Figure 4 shows an example of the logic associated to the access circuit of the RFID depicted on figure 3.

Detailed Description of the Preferred Embodiment

According to the invention, the time needed to collect a given number of samples (X₁, F(X₁)) upon which hackers rely to crack a secret information hidden in the function F is extended. The longest the time will be to potentially crack a secret information, the less interest will be found by the hacker as this information may become obsolete or as the required cracking effort may turn as unaffordable .

For sake of illustration, the description is based upon the used of passive RFID but it should be understood that the invention can be implemented with any electronic device for limiting repeated accesses, particularly with any electronic device receiving power from an external source e.g, battery free electronic devices. RFID systems

The core of any RFID system is the 'Tag' or 'Transponder', which can be attached to or embedded within objects, wherein data can be stored. An RFID reader, generi- cally referred to as reader in the following description, sends out a radio frequency signal to the RFID tag that broadcasts back its stored data to the reader. The system works basically as two separate antennas, one on the RFID tag and the other on the reader. The read data can either be transmitted directly to another system like a host computer through standard interfaces, or it can be stored in a portable reader and later uploaded to the computer for data processing. An RFID tag system works effectively in environments with excessive dirt, dust, moisture, and/or poor visibility. It generally overcomes the limitations of other automatic identification approaches.

Several kinds of RFID, such as piezoelectric RFID and electronic RFID, are currently available. For example, passive RFID tags do not require battery for transmission since generally, they are powered by the reader using an induction mechanism (an electromagnetic field is emitted by the reader antenna and received by an antenna localized on the RFID tag) . This power is used by the RFID tag to transmit a signal back to the reader, carrying the data stored in the RFID tag. Active RFID tags comprise a battery to transmit a signal to a reader. A signal is emitted at a predefined interval or transmit only when addressed by a reader.

When a passive High Frequency (HF) RFID tag is to be read, the reader sends out a power pulse e.g., a 134.2KHz power pulse, to the RFID antenna. The magnetic field generated is 'collected' by the antenna in the RFID tag that is tuned to the same frequency. This received energy is rectified and stored on a small capacitor within the RFID tag. When the power pulse has finished, the RFID tag immedi- ately transmits back its data, using the energy stored within its capacitor as its power source. Generally, 128 bits, including error detection information, are transmitted over a period of 20ms. This data is picked up by the receiving antenna and decoded by the reader. Once all the data has been transmitted, the storage capacitor is discharged, resetting the RFID tag to make it ready for the next read cycle. The period between transmission pulses is known as the 'sync time' and lasts between 20ms and 50ms depending on the system setup. The transmission technique used between the RFID tag and the reader is Frequency Shift Keying (FSK) with transmissions generally comprised between 124.2kHz and 134.2kHz. This approach has comparatively good resistance to noise while also being very cost effective to implement. Many applications require that RFID tag attached to objects be read while traveling at specific speeds by a readout antenna .

RFID tags can be read-only, write-once, or read-write. A read-only RFID tag comprises a read-only memory that is loaded during manufacturing process. Its content can not be modified. The write-once RFID tags differ from the readonly RFID tags in that they can be programmed by the end-user, with the required data e.g., part number or serial number. The read-write RFID tags allow for full read-write capability, allowing a user to update information stored in a tag as often as possible in the limit of the memory technology. Generally, the number of write cycles is limited to about 500,000 while the number of read cycles is not limited. A detailed technical analysis of RFID tag is disclosed e.g., in RFID (McGraw-Hill Networking Professional) by Steven Shepard, edition Hardcover.

Figure 1 depicts an example of the architecture of a passive HF or Ultra High Frequency (UHF) RFID tag 100. As shown, the dipole antenna comprising two parts 105-1 and 105-2 is connected to a power generating circuit 110 that provides current from received signal to the logic and memory circuit 115, to the demodulator 120, and to the modulator 125. The input of demodulator 120 is connected to the antenna (105-1 and 105-2) for receiving the signal and for transmitting the received signal to the logic and memory circuit 115, after having demodulated the received signal. The input of modulator 125 is connected to the logic and memory circuit 115 for receiving the signal to be transmitted. The output of modulator 125 is connected to the antenna (105-1 and 105-2) for transmitting the signal after it has been modulated in modulator 125.

The architecture of a semi-passive RFID tag is similar to the one represented on figure 1, the main difference being the presence of a power supply that allows it to function with much lower signal power levels, resulting in greater reading distances. Semi-passive tags do not have an integrated transmitter contrarily to active tags that comprise a battery and an active transmitter allowing them to generate high frequency energy and to apply it to the antenna .

As disclosed in "A basic introduction to RFID technology and its use in the supply chain", White Paper, Laran RFID, when the propagating wave from the reader collides with tag antenna in the form of a dipole, part of the energy is absorbed to power the tag and a small part is reflected back to the reader in a technique known as back-scatter. Theory dictates that for the optimal energy transfer, the length of the dipole must be equal to half the wave length, or λ/2. Generally, the dipole is made up of two λ/4 lengths. Communication from tag to reader is achieved by altering the antenna input impedance in time with the data stream to be transmitted. This results in the power reflected back to the reader being changed in time with the data i.e., it is modulated.

Figure 2, comprising figures 2a and 2b, shows an RFID system 200. As depicted on figure 2a, RFID system 200 comprises a reader 205 having an antenna 210. The antenna 210 emits a signal 215 that is received by an RFID tag 220. Signal 215 is reflected in RFID tag 220 and re-emitted as illustrated with dotted lines referred to as 225. Figure 2b illustrates the signal 215 emitted by the antenna 210 of the reader 205 and the signal 225 reflected by the RFID tag 220. As shown on figure 2b, the reflected signal 225 is modulated.

Logic control limiting repeated accesses

The method and systems of the invention for solving the afore mentioned problem is based on the following principles: the more frequent the RFID is accessed, the longest the user will have to wait before receiving from the RFID the expected information. This principle is based on the use of an innovative logic and innovative access circuit which are exercised before control is given to the conven- tional logic embedded within the RFID for accessing data. Figure 3 illustrates an example of a passive RFID 300 according to the invention for limiting the repeated accesses to the data of the tag. RFID 300 comprises a logic circuit 305, an access circuit 310, and an antenna 315. As illustrated, the logic circuit 300 includes the conventional logic 320 and the new access logic 325. The access circuit 310 includes a diode 330 to enforce capacitor 335 discharge direction, and a leaking resistor 340 with high resistivity. Typically the time T needed to discharge the capacitor would be of several orders of magnitude above the time duration for running the conventional logic. The access circuit 310 further includes a reset counter circuit 345, the role of which is to reset (fill with zeros) the counter 350 when powered off, after the capacitor 335 is discharged. The size of the counter 350 depends upon the implementation. This counter can count within a range from zero to C_max. Within this range are defined a set of thresholds C₁. For each threshold C₁ is associated a delay T₁. The definition of the set of parameters C₁ and T₁ depends upon the implementation, for keeping the required flexibility to use the invention in different fields, under different implementation constraints. Typically, the values T₁ will grow with index i, preferably following an exponential law.

The access circuit is directly powered from the same source as the IC executing the conventional logic, typically constituted by the RFID antenna where is received the energy radiated by electromagnetic waves.

The access logic is implemented as the first logic triggered once the IC circuit is waken-up. This constitutes the "boot strap" of conventional chips. It follows the logic described on figure 4. When the RFID 300 is powered-on, the value C of the counter 350 is incremented by one and it is read (step 400) . The value C of the counter 350 is then compared with the thresholds stored within the RFID 300 to determine the threshold C₁ such that C₁ < C < C_1+i (step 405) . When threshold C₁ has been determined, the RFID 300 is set in an idle state during delay T₁ associated to C₁ (step 410) and the control is given to the conventional logic (step 420) .

The conventional logic is typically used to access data stored within the electronic device however, it can also be used to control functions like updating operational parameters, or launching measurement operations, or triggering any embarked process.

Examples of using the system limiting repeated accesses

Let illustrate how the invention works in the following examples, where it is assumed that C₁ = i + 1 and that T₁ = 2^1"1.

First example (normal scenario)

The RFID has not been accessed since a time greater than T. Accordingly the capacitor is discharged, so that the counter is no longer powered and holds a zero value thanks to the counter reset component.

The RFID is powered and thus,

- the access logic starts, increments the value of counter C which takes the value 1 ; - the threshold C₀ = 1 is found; and, - a delay T₀ = 0 (associated to C₀) is added before giving control to the conventional logic.

In this case, one can understand that for the first access i.e., after a power-off time greater than T, the logic only introduces its own processing delay.

Second example (steps following immediately the ones of the previous example)

The RFID has been recently accessed i.e., the delay between the last access and the current one is less than T. Accordingly the capacitor is still charged, so that the counter holds its last value 1.

Then, the RFID is powered and thus,

- the access logic starts, increments the value of counter C which takes the value 2 ; - the threshold Ci = 2 is found; and,

- a delay I₁ = 1 (associated to Ci) is added before giving control to the conventional logic.

Third example (steps following the second example, after n iterations)

The RFID has been recently accessed i.e., the delay between the last access and the current one is less than T. Accordingly the capacitor is still charged, so that the counter holds its last value (n-1) .

Then, the RFID is powered and thus, - the access logic starts, increments the value of counter C which takes the value n;

- the threshold C_(n-i) = n is found; and,

- a delay T_(n__D = 2"^"1 - 1 (associated to C_n-i) is added before giving control to the conventional logic.

With values of n becoming large, the induced delay may reach very high values that may even prevent the use of the conventional logic.

Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many modifications and alterations all of which, however, are included within the scope of protection of the invention as defined by the following claims .

Claims

Claims :

1. A system in an electronic device for limiting repeated accesses to said electronic device, said system comprising,

- counting means; - counter resetting means adapted to maintain the value of said counting means for a predetermined delay after the power off of said system; and,

- logic access means adapted to increase the value of said counting means each time an access is done to said electronic device and to idle said electronic device for a delay depending upon the value of said counting means.

2. The system of claim 1 wherein said logic access means further comprise selecting means adapted to select a predetermined threshold among a set of predetermined thresholds according to the value of said counting means and to select the predetermined delay associated to said selected predetermined threshold, said system being in an idle state during the delay determined by said selected predetermined delay.

3. The system of either claim 1 or claim 2 wherein said counter resetting means further comprise a capacitor powering said counting means for said predetermined delay after said system is powered-off.

4. The system of claim 3 wherein said counter resetting means further comprise a diode to enforce the discharge direction of said capacitor.

5. The system of any one of the previous claims wherein said electronic device is adapted to receive power from an external source.

6. The system of any one of the previous claims wherein said electronic device is a Radio Frequency IDentifier tag.

7. The system of claim 6 wherein said Radio Frequency IDentifier tag is passive.

8. A method for limiting repeated accesses to an electronic device, said method comprising the steps of, - resetting a counter when said electronic device is not accessed during a predetermined delay; incrementing said counter each time said electronic device is accessed;

9. The method of claim 8 further comprising the steps of selecting a predetermined threshold among a set of predetermined thresholds according to the value of said counter and selecting the predetermined delay associated to said selected predetermined threshold, said electronic device being set in an idle state during the delay determined by said selected predetermined delay.