WO2007048399A1

WO2007048399A1 - Method for interception-proof near-field communication with inductive transponders of electronic documents

Info

Publication number: WO2007048399A1
Application number: PCT/DE2006/001895
Authority: WO
Inventors: Peter Kronegger
Original assignee: Acg Identification Technologies Gesellschaft Mbh
Priority date: 2005-10-26
Filing date: 2006-10-25
Publication date: 2007-05-03
Also published as: DE102005051493A1

Abstract

Writing and reading processes using integrated transponders can be detected and evaluated from a distance by unauthorized individuals with the aid of radio wave receivers such that privacy and sensitive data are not sufficiently protected against access. The inventive device effectively prevents such unauthorized access. The disclosed device for interception-proof near-field communication (1) comprises an interference signal source or masking signal source (3) in addition to the useful signal source (2), both of which lie within the same radio frequency band. At least one device (5) for forming a sum signal or difference signal has a strong influence on the radio wave modulation outside the reading zone. Said superposition causes the useful signal to be masked or deleted in the carrier. The inventive device provides optimal interference-proof near-field communication without requiring encoding of the communication channel.

Description

description

DEVICE FOR AUDIO-SAFE NAHFELD COMMUNICATION WITH INDUCTIVE TRANSPONDERS OF ELECTRONIC DOCUMENTS

The present invention relates to the technical field of electrical engineering, in particular to telecommunications and data transmission technology. Transponder communication devices can be read out via magnetic alternating fields or radio waves and sometimes also described. Passive transponders can also be supplied with the required energy via the radio waves. The energy and data transmission occurs contactless via electromagnetic waves. If no energy is transmitted, the transponder remains mute. During a reading or writing operation between a reader and a transponder, a magnetic alternating field is created which can be captured over longer distances with suitable receivers (radio receivers), although the distance for reading out a passive transponder is limited to a few due to the maximum permissible power of the remote feed Centimeters to a maximum of meters. To prevent or complicate such hostile interception is the cause of the use of elaborate encryption methods and coding methods. Disclosed is an apparatus for selectively preventing unwanted wiretapping of near field communications between a reader and one or more transponders. Preferably, these are passive inductive transponders with near-field antennas. The device allows the selective (Zer-) interference of signal contents or signals electromagnetic waves or alternating magnetic fields by a comparison with the prior art modified electrical circuit for Nahfeld- Kόmmunikation with inductive transponders. This restricts the range of intelligible communication between the reader antenna and the transponder antenna to the detection range of the reader, making it absolutely impossible to hear the signal outside. The main task is to protect the communication between reader and transponder by canceling or disturbing additional signal rejection.

State of the art

Electronic components are increasingly being used to secure and label or logistically monitor products and documents. RFID (Radio Frequency IDentifϊkations -) devices are miniaturized components with integrated semiconductor circuits produced for example in CMOS technology whose main terminals antennas for information transmission and possibly also for power supply are contacted. The reading of the RFID devices as a result of short as Transponder refers preferably via radio waves or magnetic alternating fields from a short distance.

Inductive transponders require an antenna coil of at least one turn, which has different shape. For example, the coil is circular, spiral, oval, or triangular and quadrilateral with mostly rounded corners. A similarly designed antenna coil is required on the communication device for reading out or writing to the transponder. With sufficient proximity of the two coils of the transponder can absorb enough energy from an alternating field and perform the data communication. This is done by modulating the magnetic field comparable to a transformer without iron core.

In order to achieve protection against transponders, various possibilities have been developed. Emphasis is put on encryption methods, whereby symmetrical or asymmetrical encryption algorithms are used. Big keys prevent any decryption of the data unless the key falls into the wrong hands.

If the private information is not transmitted but only reference numerals or reference numbers, a listening operation can only be successful if there is also an information carrier with the referenced information.

Changing the transmission channels (carrier frequency hopping) or time windows (time hopping) makes listening difficult, since a plurality of transmission channels would have to be eavesdropped at the same time.

Ultra broadband transmission enables the reduction of data transmission to very small temporal windows (secretly defined temporal ranges) and consequently very short pulse lengths.

Even shielding the entire communication path is, albeit consuming, a practiced and proven anti-interference means.

Blocker tags, designed to simulate a large number of transponder addresses, can also be used as eavesdropping protection when placed outside the communication zone.

The patent US 2005/0058292 a method and an apparatus for secure two-way communication is presented. In this case, an encrypted by a noise signal RF carrier signal is used, whereby the message of the communication is no longer extractable without the same means elsewhere by listening devices. In particular, this is experienced by a a noise signal encoded RF signal after modulation by the transponder removal of the encryption. For encryption is an amplitude, a frequency or a phase modulation circuit or combinations thereof. The modulation components are a voltage-controlled oscillator for frequency generation and modulation of the frequency or phase and / or an adjustable amplifier for amplitude modulation. In addition, a two-part coding key can be transmitted, which can also be partially varied. A password is possible. An encryption algorithm is possible. Overall, a very complex security procedure with different complexity is described, which also has a removable encryption of the carrier signal. The disadvantage is the increased system overhead, the effort to generate the reader signal and to secure the information and the effort to extract the data information. Furthermore, the modulation and Störsignalaufbringung not independent of each other possible.

Another disadvantage is the spread of the spectrum of the reader device, which regulatory approvals could not be granted.

Object of the invention

It is a cost and user-friendly device to be created, which limits the radius for authorized or unauthorized detection of transponder communication content on the radius of the maximum effective communication distance between a communication device (a reader) and a transponder. This is to make it impossible to listen to the communication contents during the writing or reading sequence outside a defined zone.

The protection request

The object is achieved by the subject invention, which is a device for monitoring near-field communication with inductive transponders of electronic. In this case, this device has a useful signal source and an interference signal source and at least one device for forming a sum or difference signal from the useful signal and the interference signal for masking or for extinguishing the useful signal. At least one device is used for local decoupling of useful signal and interference signal.

For the formation of the sum or difference signal within the device can advantageously be provided an electrical or an electronic adding circuit or an electrical or electronic subtraction circuit. Another device is mithüfe a Subtraktionsschaltung for electrical or electronic elimination of the Interference signal from the sum signal analog can be done from the difference signal by an adder circuit. As a result, the interference signal is decoupled from the useful signal again.

Alternatively or additionally, a sum or difference signal can also be generated by a device for geometric superimposition of at least two magnetic fluxes or electromagnetic waves for formation.

In this case, it is advantageous if at least one antenna is connected to the output of the useful signal source or to the output of the adding circuit for the sum signal, for example, useful and interference signal, and at least one further antenna to the output of a noise source or to the output of a subtractor is formed for the difference signal, for example, from useful and Störsignal.

Taking into account the different attenuation of a magnetic excitation with the distance, for example, from coil antennas of different diameters and different signal amplitude, the excitation by the useful signal in the near range can be higher than the excitation by the interfering signal. Conversely, in the far range, the lower attenuation of a coil with a larger diameter and with a higher interference signal level can serve to cover the useful signal.

Of particular importance is the use of a means for local decoupling of at least one antenna - for the useful signal or for a sum or difference signal with the useful signal - with respect to all other antennas of the near field communication device. This means can be, for example, a tool for the rectangular orientation of the antenna axes, such as orthogonally oriented printed circuit boards or air coils. However, it can also be a magnetically highly conductive field concentrator, for example an iron yoke or a ferrite core which has a strong filter effect near field due to the field concentration, whereas in the far field the useful signal disappears in the interference signal. A combination of the use of a field concentrator with the orthogonal orientation is also a goal-oriented means to enable the data reception in the near field. Magnetic shielding elements made of magnetically conductive material, such as iron sheets, represent a further alternative or supplementary means for local decoupling.

For recovering the original useful signal or a derived signal which carries the communication message due to the modulation by the antenna impedance variation of the transponder (eg the antenna current of the apparatus for the interception-protected near field communication), there are two possibilities. In the case of using an adder for masking or canceling the modulated useful signal is advantageous, the output of the adder with a first input of a Subtracting circuit connected, and the output of the noise source connected to a second input of the subtractor, and whose output is connected to a signal evaluation circuit.

If a subtraction circuit is used for the formation of the signal for masking or canceling out the modulated useful signal, then conversely an adder circuit is used for the signal acquisition. In this case, the output of the subtraction circuit is connected to a first input of this adder circuit, and the output of the interfering signal source is connected to a second input of the adder circuit _^ and its output is connected to a signal evaluation circuit.

The result in both cases is a signal at the input of the signal evaluation circuit, which corresponds to that of conventional unprotected near-field communication devices.

Well suited and advantageous is the use of a random value generator for switching the noise source. The value of the generator is preferably formed of a pseudo-random signal generator, a stochastic signal of a noise signal generator or the like.

To make it difficult to identify a noise source or to prevent the interference of other devices, it is advantageous that the noise source is activated, controlled or formed by the modulation signal of at least one transponder. Once a modulation by a transponder (backscattering signal) is detected by a change detector of the subject invention, the noise source is active. A watchdog circuit advantageously keeps the interference signal source active until a detector signal does not arrive for a sufficiently long time. Also, the noise source can be activated delayed, or the signal of the change detector itself serves as a noise source by means of a time delay element. Conveniently, a shift register or the like is suitable for this, as a result of which the signal at the output of the register is again added to or subtracted from the useful signal with the means mentioned.

Finally, it may be advantageous if the interfering signal source itself is the useful signal source, or equal to the useful signal source, or is formed from the caused by the Transponderantennen- impedance modulation signal, as far as possible decoupled antennas for the far field are fed destructively interferent. Thus, the antennas which are not in close coupling with a transponder can be driven invertedly, or the winding sense of the coil is different than that of the useful antenna.

The invention and possible embodiments will be described below with reference to the figures. Show it: FIG. 1 shows the principle circuit diagram with the device 1 for monitoring near-field communication and a transponder 6.

Figure 2 and Figure 3 show possible arrangements and embodiments of the antennas.

Figures 4 to 12 show embodiments of the apparatus for forming a sum or difference signal.

Figures 13, 14 and 15 show possibilities for decoupling the antennas 43 and 44, in particular for the near field.

FIG. 16 outlines a possible extraction of the transponder (backscatter) information in the case of electrical or electronic addition of interfering and useful signal.

FIG. 17 outlines a possible extraction of the transponder (backscatter) information in the case of electrical or electronic subtraction of interfering and useful signal.

FIG. 18 and FIG. 19 show sketching of different types of interfering signals.

FIG. 20 shows a possibility for generating an interference signal for deleting the useful signal in the far field by destructive interference.

As shown in Figures 1, 16 and 17, two signal generators 2, 3 for generating a Nutzsignaf and a noise signal are possible. These may have the same or similar carrier frequency. The useful signal is usually suitable for the energy supply of the transponder and approved carrier signal of certain frequency and is generated by the generator 2. This carrier signal is transmitted to a read-out transponder by the coupling of the near-field antenna 4 with the transponder antenna 61 to the transponder, which thereby absorbs energy. The variation of the energy intake e.g. by varying the input impedance of the transponder 6 is visible by a change of the primary coil current of the transformer formed by the antennas, whereby a data transport to the device 1 is made possible.

The second generator 3 serves to disturb the alternating magnetic fields or radio waves around or even within the communication distance. It generates a signal that has indefinite, ambiguous, and non-repetitive content. This useless information is only for the privacy of the communication process. By means of the device 5 for the formation of at least one sum or difference signal, an interference signal is added or subtracted from the useful signal. This can happen on the electrical level or on the magnetic level. In the second case, as indicated by dashed lines in FIG. 1 and shown in FIG. 20, an additional antenna 44 is provided for the interference signal. Then the magnetic fields of the antennas 43, 43 additively overlap. With opposite superimposition, the magnetic field components are extinguished. The geometric superposition of the magnetic fields or the radio waves is symbolized by the frame 53.

In FIG. 2, coil antennas 4, 41, 61 are used for energy and data transmission. When using a second antenna 44, this should aulweisen as decoupled orientation as useful signal antenna and transponder antenna.

FIG. 3 shows another example of the design of the near-field antenna. Here, a printed circuit, one or more printed circuit board elements or carriers of metallic or conductive layers serve to form a loop antenna 42 or a plurality of loop antennas 43, 44.

FIG. 4 shows the switching symbol of an adding function 51 as it can be embodied by the device 5. FIG. 6 shows an electrical embodiment through a current node. 1 shows an electronic addition of two signals with an operational amplifier, which originate from generators, eg in the form of an electrical alternating voltage for the useful signal and an irregularly pulsed second alternating voltage for the interfering signal.

FIG. 5 shows the switching symbol of a subtraction function 52 for the device 5. In FIG. 7, the electrical subtraction is represented by a current node, wherein the phase position of the interference signal is rotated by 180 degrees (signal inversion). FIG. 9 shows an electronic subtracter. Normally, the electronic and electrical circuits are still adjusted power output stages. If a subtraction function 52 is used, the energy is strongly attenuated at the same frequency of the useful and interference signal. At the same amplitude even extinguished. Then no data transmission can take place. If a similar frequency is used, a beat occurs, with the difference frequency, thereby generating energy supply pulses. If they are too short, the complete information can not be transferred. Additional switching on and off of the Störsignalfrequenzgebers at irregular intervals cause an interference signal, which leads to high security against eavesdropping.

If the addition or subtraction of the signals is effected by two antennas, one serving as a coupling antenna for the transponder and the second as an interfering antenna, the apparatus 5 can also be simple connections with decoupled antennas, as shown in FIG. Depending on the orientation of the antennas to each other, there is a geometric addition or subtraction of useful and interfering field components.

Figures 11 and 12 show the functional diagram when, for example, the sum signal of an adder 51 of useful signal and interference signal supplied to an antenna and the difference signal of a subtractor 52 is fed to another antenna, whereby the transponder modulates a signal changed by means of noise source. By subtraction of sum and difference signal can be easily recover the modulation signal. FIG. 13 shows a possible means 7 for decoupling the magnetic fluxes: the orthogonal arrangement of the loop antennas 42, one of which is the useful signal antenna 43 and one the interfering signal antenna 44.

Another possible means 7 for decoupling is the guidance of the magnetic flux in highly magnetically conductive materials, as set forth in FIG. The iron yoke 72, which is preferably formed by laminations, on the one hand serves for the field concentration for the useful signal, and on the other hand for the decoupling of the two windings 43, 44 for the data traffic via the transponder 6 and the interference signal generation via the antenna 44 for the environment.

FIG. 15 shows the possibility of shielding 73 of the useful field antenna 43 from the interference field antenna 44 as a decoupling device 7.

When the sum signal of the adder 51 is supplied to the communication antenna 4, a subtracter 54, as shown in FIG. 16, provides simple signal recovery capability for further processing in the signal evaluation circuit 8.

17, the principle is reversed, wherein the difference signal of the subtractor 52 of the communication antenna 4 is supplied and the adder 55, the signal for further processing in the signal evaluation circuit 8 is generated.

1, 16 or 17, where the generation of the interference signal by a "random" signal from the signal evaluation circuit 8 serves to control a switch, transmission gate or amplifier Random value generator 9 can be a noise source with window discriminator or a pseudo-random generator or else the time-shifted modulation signal of the transponder.

The latter is outlined in FIG. For the time shift, a time delay element 112 or a shift register 113 can serve. But it can also be a monoflop activated by the Tränsponder- Modufatjon. This switches on (retriggerable or not) the interference signal source for a limited time or off.

Finally, FIG. 20 shows an exemplary embodiment in which the signal of the useful signal source is tapped off and amplified is supplied to the interference signal path. As a result, with suitable control, a partial to complete extinction of the communication signal outside the near field can be effected. LIST OF REFERENCE NUMBERS

1 near-field communication device with privacy protection

2 useful signal source

3 noise source

4 near field antenna

41 coil of wound wire

42 loop antenna, formed by the conductive layer of a printed circuit

43 Antenna for the useful signal or for a sum signal of useful and interference signal

44 Antenna for the interference signal or for a difference signal from useful and interference signal

5 Apparatus for forming a sum or difference signal 51, 55 adding circuits

511 Electrical adder circuit

512 Electronic adding circuit 52, 54 subtracting circuits

521 Electric subtractor circuit

522 Electronic Subtraction Circuit

53 Device for geometric superimposition of at least two magnetic fluxes or electromagnetic waves

6 transponders

61 transponder antenna

7 means for local antenna decoupling

71 means for orthogonal orientation of the antenna axes

72 field concentrator (ferrite, iron core)

73 magnetically conductive shielding plate

8 signal evaluation circuit (typical reader evaluation circuit)

9 random number generator

10 change detector

11 control circuit

111 watchdog circuit

112 time delay element

113 shift registers

12 amplifiers

Claims

claims

1. Device (1) for the tap-proof near-field communication with inductively coupled transponders (6), characterized in that the device (1) a useful signal source (2) and a Störsignalquelle (3) and at least one device (5,53) to form a Has sum or difference signal from the useful signal and the interfering signal, and at least one device (8,53) is provided for local decoupling of useful signal and interfering signal.

2. Device (1) according to claim 1, characterized in that a device (5) for forming a sum or difference signal, an electrical (511, 521) or electronic (512, 522) adding (51) - or subtracting (52) Circuit and a device (8) for electrical or electronic elimination of the interference signal from the sum signal by means of a subtraction circuit or from the difference signal by an adder, whereby the interference signal is decoupled from the useful signal.

3. Device (1) according to claim 1 or 2, characterized in that a device (53) for forming a magnetic or electromagnetic sum or difference signal from useful signal and interference signal in the near field as possible decoupled geometric arrangement.

4. Apparatus according to claim 3, characterized in that for transmitting the useful signal and for superposition by the interference signal at least two near-field antennas (43,44) are provided, preferably in the form of a coil (41) or conductor loop of wound wire or as a printed circuit (42) are implemented with at least one conductive layer of a printed circuit board material.

5. The device according to claim 4, characterized in that the device (53) by at least one antenna (43) to the output of the useful signal source (2) or to the output of the adder circuit (51) is connected, and at least one further antenna (44 ) is connected to the output of the interfering signal source (3) or to the output of the subtracting circuit (52).

Device according to Claim 5, characterized in that it comprises means (7) for local decoupling of at least one antenna (43) from all other antennas (43, 44) of the device (1), preferably means (71) for orthogonal orientation the antenna axes, a magnetically highly conductive field concentrator (72), for example, an iron yoke or a ferrite core and / or a magnetic shielding element (73) of magnetically conductive material, for example made of sheet iron.

7. The device according to at least one of claims 1 to 6, characterized in that the output of the adder circuit (51) is connected to a first input of a subtraction circuit (54), and the output of the interference signal source (3) with a second Input of the subtractor (54) is connected, and whose output is connected to a signal evaluation circuit (8).

8. The device according to at least one of claims 1 to 6, characterized in that the output of the subtractor (52) is connected to a first input of an adder circuit (55), and the output of the interference signal source (3) having a second input the adder circuit (55) is connected, and whose output is connected to a signal evaluation circuit (8).

9. Device according to at least one of claims 1 to 8, characterized in that the interference signal source (3) is switched by a random value generator (9) whose value is preferably formed from a pseudo-random signal generator, from a stochastic signal of a noise signal generator.

10. The device according to at least one of claims 1 to 9, characterized in that the interference signal source (3) by the modulation signal (backscattering) at least one transponder (6) via an amplitude signal change detector (10) is activated, is preferably controlled as a control circuit (11) a watchdog circuit (111), a time delay element (112), a shift register (113) is used.

11. The device according to at least one of claims 5 to 10, characterized in that the interference signal source (3) by means of at least one amplifier (12) is formed from the signal caused by the transponder antenna impedance modulation, with as decoupled antennas (43,44 ) for the far field are destructively fed interferent.

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